This review article synthesizes research from several disciplines by conceiving of the Earth as an open system significantly influenced by inputs of matter from outer space. It carefully and critically surveys the topics of mass extinctions, interplanetary dust/micrometeorites, delivery of complex pre-biotic organics molecules from space, ice ages, small comets and panspermia. The evidence, if verified by continuing investigations, shows that the Earth was an open system just after planet formation. Since then, the Earth has been significantly influenced by inputs of extraterrestrial matter, but the inputs are not critical to the sustained functioning of the system.
Acknowledgements
The author would like to thank the following individuals for their invaluable assistance:
Michael A. Salay, Ph.D.; Brian F. Rauch, M.S., M.A.; Charles R. Greenwell, M.S.
This review article synthesizes research from several disciplines by conceiving of the Earth as an open system significantly influenced by inputs of matter from outer space.[1] While this would not be a scientific revolution on par with the Copernican, it would nonetheless be a fundamental paradigm shift. A university level astronomy textbook published in 1978 stated, "Asteroids and meteoroids are other residents of our solar system. We shall see how, along with the comets, they may prove to be storehouses of information about the solar system's origin."[2] Treating asteroids as relics has been forcefully revised by the well-publicized findings that an asteroid impact triggered the extinction of the dinosaurs and cleared the way for mammals. In 1985, an eminent geophysicist commenting on mass extinction wrote of asteroids, "A fraction of these are large enough to survive the trip through the Earth's atmosphere."[3] But during the 1990s, research into interplanetary dust and micrometeorites revealed that a highly relevant question is whether the object is small enough to survive the trip (see section 3).
The current dominant paradigm is expressed by a recent Earth System Science text which explains that it covers:
2. The flows of energy (Earth is an open system with respect to energy); and
3. The web of life (Earth is a networked system with respect to life.)"[4]
Yet almost simultaneously, geology professor Csaba Detre was writing that, "Today it is obvious that the main events in the Earth's history have cosmic origin, because the Earth is not a closed system, but a mirror of cosmic events, an inseparable part of the Universe."[5] And professors James and Jessie Miller, pioneers of system science, were writing that, "The Earth is an open system, interacting with its atmosphere and with matter and energy in space."[6]
Textbook thermodynamics informs us that an isolated system is one with a boundary that allows neither energy nor matter to pass. This is a concept that exists in the ideal realm, but a well-insulated thermos is an approximation. A closed system is one that allows the exchange of energy, but does not allow matter to pass. A battery is an example. An open system is one whose boundary passes both energy and matter.[7]
It is fundamental that the Earth is at least a closed system. The input of solar energy in the form of visible light and infrared radiation is essential for photosynthesis and a habitable planet temperature. Without these the planet would feature a severely hobbled biosphere, atmosphere and hydrosphere. The surface would be frozen, pitch-black, lifeless, with almost no wind. Life would still exist up to 10 kilometers below the surface[8] and around deep ocean hydrothermal vents,[9] which are the only places where water would flow freely, thawed by the Earth's internal heat. In these places chemosynthetic life, which derives energy from chemicals such as hydrogen sulfide, is at the bottom of the food chain. Conversely, the escape of excess infrared radiation prevents the planet from becoming an oven like Venus.
Recent thinking is pointing to the conclusion that perhaps the Earth is an open system with respect to matter- a direct reversal of point 1 above. Inputs of extraterrestrial matter into the terrestrial sphere may have made a continuing vital contribution throughout the existence of the planet. This manuscript assesses the following areas of open systems research: mass extinctions, interplanetary dust/micrometeorites, delivery of complex pre-biotic organic molecules from space, ice ages, small comets and panspermia.[10] It does not cover cosmic rays,[11] solar wind particles and the contribution of supernovae to mass extinctions[12] due to the need to limit the scope. The areas covered are very interesting findings that deserve to be thoroughly considered.
2. Impact Events and Mass Extinctions
The most empirically verified evidence in support of the concept that the Earth is an open system comes from impacts of large objects (bolides) such as comets and asteroids. Since most of this topic is well-covered even in introductory textbooks it shall be treated here with apologies and only as necessary to elucidate the open system concept.
Large bolide impacts account for only 5% of the mass of the extraterrestrial matter reaching Earth. The Cretaceous-Tertiary (K-T) boundary impact of 65 million years ago was probably the trigger event for the extinction of the dinosaurs, allowing the rise of mammals and ultimately the evolution of humans. Bolide impacts have been implicated as the triggering or a contributing factor in at least six mass extinctions in the past 400 million years,[13] including the mass extinction at the Permian-Triassic boundary (251 million years before present.). This was the most extensive mass extinction known, and it is the one that cleared the way for the dinosaurs.[14] There are over 150 surviving craters around the globe, several with diameters in the 80 km range.[15] An ongoing project using remote sensing aims to uncover craters previously undetectable due to the erasing processes oferosion, sedimentation, volcanism and plate tectonics.[16]
This evidence establishes that the Earth system has been significantly influenced by inputs of extraterrestrial matter. Things would not have turned out the way they have in the sense that humans and even the dinosaurs might never have existed. Yet this evidence does not establish that the planet is an open system in the way that a life form is, because the planet would still be able to sustain itself without these impacts; in fact it would still have a thriving surface biosphere.
It is useful to consider the competing explanations for why these bolide impacts occur, because they illustrate some possible connections of the Earth to the cosmos. Probably the standard explanation for asteroid impacts is that the gravity of Jupiter or Saturn periodically yanks a large asteroid from the asteroid belt and puts it on a course that intersects the orbit of the Earth. Going a bit further, there is a proposal that a yet unobserved Planet X disturbs the Kuiper belt of comets,[17] dislodging some into an intercept course with Earth. It is these comets which cause mass extinctions when they collide with the planet. A third explanation is the galactic plane hypothesis. Our solar system in fact is not stationary, but moves vertically in the Milky Way galaxy as the galaxy itself rotates in space. During its journey, our solar system encounters dense clouds of interstellar gas and dust.[18] These interstellar clouds are thought to exert a gravitational influence on the Oort cloud of comets,[19] dislodging some of the billions of comets contained there. Galactic cycles drive evolution on Earth. A fourth proposal is the Nemesis hypothesis. A yet unobserved companion star to the sun, probably a red dwarf with a highly elliptical orbit, periodically passes near enough Oort cloud to yank some from their orbits and send them towards Earth.[20]
2.1 Outputs of Life-Bearing Meteorites From Earth
By definition, a thermodynamically open system also requires output of matter. There are few, if any, theoretical objections to the possibility that some rocks of Earth origin have reached Mars and other planets in the solar system.[21] We know for certain that the process works the other way- at least 12 meteorites of Mars origin have been collected.[22] If a meteorite in the size range of the Chicxulub bolide hit the Earth, the impact would eject a variety of substances into the atmosphere, and some of the rocks would be at escape velocity (11 km/sec). A fraction of these would reach other planets in the solar system after a voyage that in theory would take about 10 million years. We know that bacteria exist in the interior of rocks,[23] we know that bacteria are extremely hardy, being able to survive high doses of radiation and extremes of temperature, and we know that bacteria reproduce extraordinarily rapidly.[24] Any bacteria in ejecta rocks would be relatively protected by the rock itself. If even one bacterium survived in the interior of a rock ejected from Earth, upon arrival at another planet, that bacterium could exfiltrate the rock, find a medium in which it could survive and begin reproducing.[25] The scenario considered most likely is that a piece of ejecta of Earth origin might have landed on Mars during the period billions of years ago when it appears that Mars had surface water and a thicker atmosphere than now. This rock contained Earth bacteria which took root on Mars, so that the Earth seeded Mars with microscopic bacterial life forms, which is thought to be as far as life ever got on Mars. The scenario could also work the other way- early Mars seeded the early Earth with microscopic life, which took root and flourished on Earth.
3. Micrometeorites and Interplanetary Dust
Some 95% of the mass of extraterrestrial matter reaching the surface of the Earth is "space dust."[26] The Infrared Astronomy Satellite's observations indicate that micrometeoroids (MM) and interplanetary dust (IPD) pervade the solar system.[27] The main sources of MM and IPD are dust vented by comets and debris created by collisions between asteroids in space. [28] For example, Halley's comet generated roughly one hundred million tons of particles during its last flyby of the sun in 1986.[29] The particles drift into the inner solar system due to solar and planetary gravity,[30] Poynting-Robertson drag,[31] and solar wind drag, [32] where some encounter the Earth.
Currently, about 40,000 metric tons per year of MM and IPD cross the orbit of the Earth and enter the atmosphere.[33] There are spikes in the flux of MM and IPD due to asteroid collisions and comet activity. These are caused by the gravitational pull of the sun, the gas giants and nearby stars. These large bodies influence the orbits of asteroids, resulting in collisions, and pull dormant comets out of their positions in the Ort Cloud and Kuiper Belt and towards the sun. Asteroid collisions may result in an accretion spike of 107 tons per year for 10,000 years.[34]
MM and IPD are microscopic. MM range in size from 50-400 micrometers (µm),[35] while IPD is about 50Å -40 µm in diameter. [36] The different names for the particles are solely due to their different sizes. The particles are studied under electron microscopes at up to 7000x magnification. Detailed analysis of the particles has been made possible by the development in the 1990s of mass spectrometers of enhanced sensitivity.[37] The typical particle is a heterogeneous composite of material found in terrestrial rocks such as ferro-magnesian minerals,[38] certain elements such as iridium generally found meteorites but not in terrestrial rocks,[39] organic carbon based compounds and amino acids (10%)[40] and radiogenic isotopes formed in space due to exposure to solar radiation.[41] It is the iridium and radiogenic isotopes which identify the particles as exogenous to Earth.
A portion of the particles, perhaps 50%, survive entry and reach the surface.[42] A much higher ratio of MM and IPD survive entry than do their larger cousins, the meteoroids and asteroids. This is because an object is fully decelerated if it encounters its own mass of air molecules and therefore will not burn up but rather drift to the surface of the Earth. Given the high ratio of surface area to mass of these particles, they have a greater chance of decelerating.[43] To get an idea of how unexpected this is for science, consider that geophysicist David M. Raup, one of the most open-minded scientists with respect to the extraterrestrial input of matter, wrote in 1985 of meteorites, "A fraction of these are large enough to survive the trip through the Earth'satmosphere." MM and IPD have simply upset the established knowledge of only a short time ago.
Over geologic time, the yearly flux has accumulated. If we use an estimate of 20,000 tons per year accretion rate,[44] and assume that the rate has been constant[45] since the end of the heavy bombardment (4 billion years), this yields 8 x 1013 tons of accumulation. For comparison, this is about 3 times larger than the mass of Mars' larger moon Phobos, which is estimated to be 2.73 x 1013 tons. [46] However, the mass of accumulated material is still far smaller than the mass of the moon, estimated to be 7.35 x 1019 tons. [47]
4.1 The ice ages and the Earth's climate
The Milankovitch theory states that the changes in the Earth's orbit lead to variations in the amount of solar radiation reaching the atmosphere, causing ice ages and warming cycles. There are three types of orbital changes. First, the orbit of the Earth is not circular, but elliptical, and the eccentricity of this ellipse varies over a 100,000 year cycle. Second, there is a tilt or obliquity to the Earth's axis relative to the plane of the solar system, and this cycles over a period of 41,000 years. Third, at any given obliquity, the Earth's axis is wobbling like a top over a 21,000 year cycle and this is called precession.[48]
The Milankovitch theory has been tested and refined by hundreds of investigators since the eponymous Milutin Milankovitch, a Serbian mathematician working during the 1920s.[49] One landmark article (Hays, Imbrie and Shackleton, 1976), compares the Earth's climate history to its orbital history and concludes that the 100,000 year eccentricity cycle has been the predominant driver of the ice ages, although precession and obliquity do explain some climatic variance. The authors do not specify how changes in the delivery of solar radiation to the atmosphere translate into changes in climate: "We avoid the obligation of identifying the physical mechanism of this response...". This is not a failing of the authors; rather it reflects the current limits of scientific knowledge.[50]
The Milankovitch theory explains only a part of the phenomenon we seek to understand. Between an ice age and a warm period there is a 5 degree Celsius difference in the average global temperature. Yet the change in solar energy reaching the Earth due to orbital eccentricity accounts for only a .15 degree Celsius temperature change.[51] The rest of the 4.85 degree C temperature change is thought to be due to climatic feedback effects, but there is no consensus understanding on how these work. [52] Nor do we know what triggers (forces) ice ages. One of the leaders in the field opined in 1998, "We have but simple theories for the ultimate forcing of climate change, even in recent times."[53]
Milkanovitch is the reigning theory because it is the most validated model we have. We can be sure that this small piece of the puzzle is accurate. Since science knows so little about how the ice ages start and terminate, when a new piece of knowledge becomes available, such as MM and IPD, scientists in various fields hope that the new information will resolve long standing dilemmas.
Muller and MacDonald (1995, 1997) argue that for the ice ages of the past 1 million years, the cause may have been MM and IPD.[54] They note that for the past 1 million years there has been a 100 thousand year climate cycle. As stated above, this had been thought to match the eccentricity cycle, but Muller and MacDonald report that the inclination of the orbital plane of the Earth has also been shown to happen in a 100,000 year cycle.[55] This is a fourth characteristic of the Earth's orbit: the plane of the Earth's orbit varies from being perfectly level with the sun.[56] Muller and MacDonald present a series of elegant graphs that match the ice age predictions of the orbital inclination theory to the actual data on the climate cycle, and argue that the inclination theory is the best fit to the climate data:
Figure 1. Column A represents the predicted ice age frequency based on three theories. First is an eccentricity based model, second is a precession based model, and third is Muller and MacDonald's orbital inclination based model. The orbital inclination model clearly and cleanly predicts an ice age every 100,000 years. Moving to columns B,C and D, &Mac182;18O is an isotope that is a proxy for global ice levels. A spike in the &Mac182;18O level indicates an ice age. The orbital inclination model is the best match for the empirical data in these three columns. Science 277 (1997); 215-218, figure 3
What about an increased angle of inclination causes an ice age? Orbital inclination has no significant effect on solar insolation.[57] They hypothesize that the Earth's orbital plane is tilting into a massive stream extraterrestrial dust and that the dust is the trigger mechanism of the ice ages. This theory has received empirical support from a series of analyses of ancient sediment which have shown that there is a 100,000 year periodicity in the accretion rate of MM and IPD, with a sudden increase in the amplitude of the cycle beginning 1 million years ago and continuing today.[58] Muller (1997) concluded, "As far as we know, none of the present climate change models include the effects of dust and meteors. And yet our data suggests that such accretion played the dominant role in the climate for the last million years."[59]
Muller does not identify the precise atmospheric or combined mechanism by which the extraterrestrial dust influences the climate, but Hays, Imbrie and Shackleton (1976) also do not specify a mechanism. K.A. Farley contends that aerosol cooling cannot be the mechanism at work.[60] He maintains that even at the peak of the 100,000 year cycle there is not enough extraterrestrial dust to cause an aerosol cooling effect.[61]
Kortenkamp and Dermott analyze the Muller and MacDonald hypothesis and find against it.[62] They assert that most of the dust probably comes from asteroids and agree that there is a 100,000 year periodicity in dust flux from the asteroid source. However, based on their simulations of dust particle orbits and the Earth's orbit, they conclude that the dust is not concentrated in any particular plane. Instead, the cause of the dust periodicity cycle is indeed the eccentricity of the Earth's orbit. The Earth accumulates up to 3 times more dust during the circular phase of the eccentricity cycle. This is because when traveling in a circular orbit the Earth moves more slowly through the cloud of dust particles, which lowers the velocity of the particles relative to the Earth, making the Earth's gravity more effective at capturing the particles.[63][64]
Kortenkamp and Dermott present their own hypothesis in place of Muller and McDonald's.[65] They note that our current knowledge suggests that many asteroids are clumps of rocky rubble held together by their own weak gravity. If an asteroid of 10 km - 100 km radius was broken apart in a collision with another asteroid, that would "instantaneously liberate," as they put it, a mass of MM and IPD up 10,000 times greater than the normal amount in the solar system. Such an event would occur once every few tens of millions of years. It would lead to about 1010 kg/year of MM and IDP hitting the stratosphere,[66] the same amount of dust pumped into the stratosphere by a volcanic eruption.[67] This would continue for about 10,000 years as the space dust is gradually captured by Earth's gravity. Since volcanic eruptions are known to cool the climate, 10,000 years of such effects "may lead to substantial changes in the Earth's climate lasting for many millions of years." Additionally, some of the debris would be in the kilometer size asteroid range, which material would arrive in an Earth-crossing orbit towards the latter end of the dust input. The cumulative result of the rubble input could be a gradual mass extinction, the authors note.
Kortenkamp and Dermott's hypothesis would seem to merit investigation by climatologists. [68] Most volcanic aerosols of terrestrial origin settle back to the ground in days or weeks. Only a small fraction reach high enough altitude to remain aloft for extended periods of time. Yet every single particle of asteroidal dust would be injected into the upper atmosphere and so remain airborne for months. The recent Pinatubo eruptions involved far less material and caused a measurable cooling. Even if the dust influx caused cooling of only a few tenths degree, that could be enough of a trigger because the cause-effect relationship is probably non-linear.[69]
One possible causal sequence is that a large spike of asteroidal dust could contribute a significantly greater supply of cloud condensation nuclei, thus increasing the numbers of clouds, which would increase the albedo of the Earth, which could in turn lead to an ice age.[70] Cloud condensation nuclei are small particles from .2 microns up to >1 micron in size which pervade the atmosphere. To be effective, the nuclei must be hygroscopic - water attracting. Water vapor condenses around these particles, leading to cloud formation. Without condensation nuclei, relative humidities of several hundred percent would be required before vapor condensation could begin.[71] Several questions would need to be investigated in order to evaluate this hypothesis. We know the baseline size distribution of MM and IPD (see fn 22 and 23). But we are here dealing with exceptional events that cause a spike in the baseline rate. Do these collisions deliver enough particles at the sizes conducive to cloud formation? Are the particles conducive to the condensation process? The answers might differ with each asteroid collision because different bodies have unique characteristics.
The possible involvement of extraterrestrial matter in glacial cycles suggests that inputs of matter have significantly influenced the atmospheric component of the Earth system, and in turn, the biosphere. The research may have some impact on the debate over global warming. Professor Stephen H. Schneider of Stanford writes, "...we cannot forecast the future accurately without understanding and modeling a great deal of the Earth's past.[72] ... We also need to understand and be able to model the factors that might induce changes in climate, factors we call forcings."[73] Mark H. Thiemens, professor of chemistry says, "One always hears the argument, 'Isn't this all part of a natural cycle?' To answer this question, you really want to have a large scale record."[74] MM and IPD may be necessary components to such an understanding.
Matter arriving from interplanetary space delivered prebiotic molecules to the early Earth. Meteorites, MM and IDP have been found to contain amino acids, other organic matter and cell like structures which do survive entry into the Earth's atmosphere and could have served as an advanced starting point from which life could develop.[75] The heavy bombardment ended about 4 billion years ago, and the oldest fossilized sample of primitive microscopic life is about 3.8 billion years old.[76] So the current state of research suggests that life emerged very quickly - only 200 million years after the end of the heavy bombardment. It is hypothesized that could life have emerged so quickly if the delivery from outer space of complex pre-biotic molecules "jump started" the process.
During the heavy bombardment, the rate of input of extraterrestrial matter was 100-1000 times higher than at present. Such a rate over 500 million years duration of the bombardment would have left a substantial accumulation of organic matter and amino acids near the surface of the Earth. This starting material might have been transformed by natural processes into proteins and other complex molecules which became life forms.[77]
Does the current gentle dusting of MM and IPD have any impact on the ecology of the planet? MM and IPD are heterogeneous composites of varieties of minerals and elements as small as 50 angstroms.[78] How long does it take the whole particles to be broken down by weathering and other processes on Earth, so that their constituent parts are available for the uptake into the biosphere? If we know this period, can we then estimate what the interval should be between an increase in the accretion rate and a possible enrichment of life on Earth? One relevant finding is "cryoconite" from Greenland. In Greenland relatively pure samples of extraterrestrial dust are found in melting glacial ice. The physics of the glacial flow causes terrestrial and extraterrestrial dust particles to concentrate as a sediment in pools of water on the surface of melting glaciers. The dust is encased in a cocoon of algae and bacteria. This entire complex is the cryoconite. The only apparent nutrient source is the dust. However, it is not determined if the algae and bacteria are living off the extraterrestrial or terrestrial dust or both. [79] Most soil scientists, biologists and ecologists don't know about MM and IPD, so have not been alert to its possible influences.[80] We shall return to this issue when we discuss the panspermia hypothesis.
This line of inquiry might show that an exogenous input was necessary to set in motion the biosphere component of the Earth system. However, it might also be interpreted as necessitating a redefinition of planet formation. Every written source I have encountered speaks of planet formation as a distinct process followed by the heavy bombardment. Because the heavy bombardment was an inevitable culling of debris which appears to have had a large impact on the character of Earth, perhaps we should not consider a planet formed until after the heavy bombardment has finished.
Other research suggests the possibility that the delivery of extraterrestrial matter may have stimulated and enriched the Earth's biosphere in the geological recent past. Culler et al. (2000) conduct an analysis of lunar soil samples returned by the Apollo 14 mission.[82] They found that the rate of meteorite impact declined from the heavy bombardment until about 400 million years ago. This is in accord with standard theory. However, they also find that from 400 million years ago to present, the rate of impact increased by a factor of 4. The impact trend for the Earth would be very similar to that of the moon due to their proximity, except that the Earth would have approximately double the rate since it is a larger target and has stronger gravity. Culler et al. note that their data indicating a pronounced spike in extraterrestrial input is "roughly coincident with the 'Cambrian explosion' of complex life on Earth. ... the correlation is permissible evidence of a causal relation. It is possible that the increased debris influx had a net stimulating effect on biotic diversity ..." The trend they highlight would also indicate a similar increase in the quantity of MM and IPD reaching the Earth. This is because an increased cratering rate could be due to both asteroids and comets, both of which are associated with MM and IPD.
The existence of small comets would go a long way towards establishing that the Earth is an open system. These comets would, over geologic time scales, be responsible for supplying much of the planet's water. Without this extraterrestrial input, the Earth would be a barren planet.
For approximately the past 15 years, a debate has been raging in astronomy and allied disciplines over the existence of small comets. First proposed by Frank, Sigwarth and Craven in 1986, this hypothesis holds that the Earth is struck by millions of water-laden comets per year with an average size of 40 feet in diameter. The comets are composed mostly of water snow. As they approach the Earth they become a cloud of water vapor at approximately 800 miles altitude. This cloud of mist loses its coherence and enlarges while it descends towards the Earth. Frank et al. argue that small comets have, over geologic time, contributed much of the Earth's oceans. It is the supply of water from small comets that continually replenishes the water lost to subduction to the interior of the planet and prevents the surface of the Earth from becoming dry and barren.[83]
There have been several dozen articles for and against small comets. For example, one group of scientists used an optical telescope to search for small comets.[84] They found nothing, although their results did not rule out the existence of the phenomenon. Frank and Sigwarth conducted their own optical search using the same telescope and they found small comets.[85] Both results were published in a prestigious peer reviewed journal and so cannot easily be discounted. I evaluated the debate by focusing on one detection method and reading the sequence of articles very carefully. By focusing in depth on a specific facet of the debate, I hoped to reach definitive conclusions which, although limited only to one detection method, would nevertheless be revealing.
In 1997, a group of radar scientists and astronomers (Knowles et al.)[86] conducted a radar search for small comets. They used the United States Naval Space Surveillance System radar. This radar has transmitter and receiver sites across the southern United States and a central data processing facility in Virginia. It is designed to catalog and track essentially all the world's Low Earth Orbit satellites. The authors state that this is the best available radar in the world for locating small comets because it searches an extremely wide volume of space with very high sensitivity. Some narrow aperture radars, (radars designed to search a small volume of space very carefully), are more sensitive, but these might miss the small comets because they do not have a wide enough field of view.
During the approximately 1 month of searching with the radar, some 12,000 unidentified targets were observed. Of these, none fit the theoretical characteristics of small comets. 50 were signal noise, and the rest were either new satellites, moving too slowly to be small comets or were in gravitationally bound orbits (not unbound infalling objects).
Frank and Sigwarth were given the opportunity to reply to the negative radar results. Knowles et al. then replied to the reply. This author has carefully analyzed the exchange and found that none of Frank and Sigwarth's objections are valid. This analysis is included as Appendix I. The results of the Naval Space Command radar observations seem to be strong empirical evidence against the existence of small comets.
Dr. David Deming explores the possibility that interplanetary dust and small comets provide the necessary carbon and water for a vibrant biosphere on Earth. [87] His ideas are unorthodox yet relevant to the Earth-as-open-system concept. Deming challenges the prevailing theory of balanced carbon and water cycles. According to Demming, the current state of scientific knowledge clearly indicates that far more carbon and water is carried down into the mantle by subduction than is released back into the ocean and atmosphere by volcanic outgassing. There is a 56-90% deficiency for carbon, and it is worse for water. Although too much carbon results in a runaway greenhouse effect, atmospheric carbon is necessary in order to prevent sun's heat from escaping back to space. Water is of course essential to life. With such a rate of carbon and water loss, the surface of the planet should be extremely cold and dry- inhospitable to a vibrant biosphere. Deming explores the possibility that extraterrestrial sources- interplanetary dust and small comets - balance the carbon and water cycles. Deming cautions that "what is being proposed is É a working hypothesis subject to being tested and possibly disproved." (p. 34).
Deming notes the Muller and MacDonald article theory that the 100,000 year orbital inclination cycle may cause the Earth to tilt into and out of a stream of interplanetary dust. He proposes that this dust stream adds carbon to the atmosphere, which causes warming. An ice age occurs when the Earth tilts out of the dust stream because the carbon content of the atmosphere falls so that the planet retains less heat.
Deming spends much of the article addressing small comets. These are thought to be 10% carbon and 90% water. Specifically, we need .6-3 x 1011 kg of carbon per year to balance the carbon cycle, and small comets are supposed to supply .2-1 x 1011 kg of carbon per year. We need 1-2 x 1012 kg of water per year to balance the water cycle, small comets are thought to supply .2-1 x 1012 kg per year. Given all the uncertainties, the area of overlap is satisfactory for Deming to hypothesize that small comets are the missing input.
Deming concludes, "Life on Earth may be balanced precariously between cosmic processes which deliver an intermittent stream of life sustaining volatiles from the outer solar system or beyond, and biological and tectonic processes which remove these same volatiles from the atmosphere by sequestering water and carbon in the crust and mantle." Deming seeks to use new information to fill gaps in the existing knowledge. Although small comets appear to be the perfect fit, the case for them is very weak at the current time.
We have covered sufficient material to return to a discussion of the ice ages. In Cometary Impacts and Ice-Ages (2001),[88] two internationally recognized astrophysicist/ mathematicians discuss the impact of not just comets, but all bolide objects, on ice age cycles. They note that there should be no way for the Earth to emerge from an ice age due to positive feedback. As more glaciers form, the Earth's albedo increases, which means that more heat from the sun is reflected back into space. This makes the Earth colder, which causes more glaciers to form. A major event would be needed to disrupt this process.
Hoyle and Wickramasinge contend that the presence of water vapor in the atmosphere is actually more important to the maintenance of a warm Earth than the amount of carbon dioxide. This is because, compared to carbon, water vapor absorbs a larger part of the spectrum of infrared radiation (heat in radiation form) that otherwise would escape back into space. An increased concentration of water vapor in the atmosphere would therefore increase the mean temperature at the Earth's surface. As Hoyle and Wickramasinghe put it, "The impact of a kilometer-sized object, (or a slightly smaller asteroid) into a major ocean appears essential to the ending of an ice-age." Such objects have undoubtedly impacted into the open ocean, leaving no trace yet kicking up enormous amounts of water vapor which would persist in the atmosphere for a period of months to years and cause a spike in the Earth's temperature. This increase in the temperature would be the trigger that ends the ice age.
Hoyle and Wickramasinghe calculate that the impact of comet or meteorite 1 kilometer in diameter would occur at a rate of one every 100 thousand years- the same as the ice age periodicity. They point to several incidents of very rapid temperature increases in the climate and fossil records. Ice cores from Greenland and Antarctica (dated to about 14,600 and 11,500 years ago) show a temperature rise of some 12-15 degrees C in only a few decades. Fossil insect records show that the mean summer temperature in Britain rose at least 10 degrees C during the same period, "an essentially decisive indication of a catastrophic event asits cause." This article presents a hypothesis that should stimulate field researchers to gather empirical data confirming or falsifying it.
The major weakness of the hypothesis is that the authors make no mention of volcanism. Hoffman and Schrag have outlined how CO2 released from volcanoes is the primary factor in causing the Earth to emerge from the most severe, overwhelming ice age known as "snowball Earth."[89] This episode occurred approximately 600 million years ago. During the snowball Earth episode, volcanoes emitted CO2 at their regular rate. Normally, this input of CO2 is counteracted by the removal of CO2 by the weathering of silicate rocks (75% of the Earth's crust is rocks of this type). Weathering of the rocks produces bicarbonate, which incorporates the carbon and oxygen atoms of CO2. Trapped in bicarbonate, the CO2 is washed into the ocean and becomes sediment. But during snowball Earth, most of the planet's H2O was in solid form, so the weathering did not occur. As a result, CO2 of volcanic origin builds up in the atmosphere to extremely high levels. This raises the temperature and brings the planet out of the ice age.
Even for the majority of ice ages, volcanism must play a greater role than Hoyle and Wickramasinghe concede. In these less severe glaciations, a great portion of the planet's H2O would still be ice, so weathering of silicate rocks would be less and there would be some buildup of CO2 from volcanoes. Impacts of bolides into the open ocean could be a primary trigger ending many ice ages, but not the only factor.
9. Panspermia and the Open System
Noted astrophysicist/mathematicians F. Hoyle and N.C. Wickramasinghe make numerous points in their research. The three most credible are:
1) Life in the form of microbes (bacteria and viruses) pervades the universe in the interior of comets, meteorites and in clouds of interstellar dust.
2) Life from outer space was delivered to the early Earth so that the origin of Earthly life is extraterrestrial.
3) Extraterrestrial microbes have continued to be delivered to Earth in the form of comet dust and interstellar dust filtering through the atmosphere to the Earth's surface.
The ideas of Hoyle and Wickramasinghe have gained a surprising degree of acceptance among well-credentialed scientists affiliated with prestigious institutions. For example, their ideas pervade the 1999 conference proceedings for the International Society of Optical Engineering (SPIE).[90] Optical engineers are relevant experts because they design and operate the microscopes of extremely high magnification that can pick up the faint traces that life (arguably) has left in the interior of meteorites. A professor geochemistry in 1990 reviewed the relevant findings regarding points 1 and 2 above and concluded, "... it is felt that a panspermistic approach to the initiation of life processes on Earth would not appear outside the mainstream of contemporary scientific thought."[91]
Most of the ideas of Hoyle and Wickramasinghe are expressed as empirically verifiable hypotheses. We shall address each theoretical contention and its empirical verification. What follows is, of necessity, a brief coverage of a lifetime of work by two extremely keen minds who benefited from frequent collaboration of co-authors from applicable disciplines.
Hoyle and Wickramasinghe envision the Earth as an open system. Genesis either occurred on Earth and was spread to the rest of the universe or, life started somewhere else and eventually extraterrestrial bacteria gained a foothold on Earth. Hence, at the outset, a crucial input or output of matter occurred. If continued input of extraterrestrial microbes is essential to the evolution of life, then inputs of matter are essential to the continued viability of the biosphere subsystem.
9.1 Life and (near-life) in the form of bacteria and viruses (together called microbes) pervades the universe in the interior of comets, meteorites and clouds of interstellar dust.
NASA researchers in collaboration with researchers from the Russian Academy of Sciences analyzed several carbonaceous chondrite meteorites (named Murchison, Mighei, Efremovka, Murray, Nagoya) at magnifications of 2000-20,000x. They found fossils of bacteria, nanobacteria (very small bacteria) and remnants of microbiological activity in deep interiors of severalmeteorites. "These forms were found in-situ in freshly broken, interior surfaces of the meteorite."[92] Some scientists argue that the microfossils found by NASA McKay et al. (1996) in the Mars meteorite are actually due to terrestrial contamination.[93] If earthly bacteria can penetrate to the interior of meteoritic rock, this coupled with the acknowledged existence of bacterial extremophiles (see page 32) means it is also possible that bacteria lived in the rock and when the rock hit Earth, some minuscule portion of the bacteria survived and exited the rock to colonized the planet. It is two sides of the same coin and those that argue for contamination are assuming terrestrial genesis, when it is also plausible to assume extraterrestrial genesis, perhaps on another Earth-like planet. If life could have started on Earth, then it also could have started somewhere else.
The absorption spectra of interstellar dust and comets provide evidence that these objects contain living microbes (bacteria and viruses. Different materials absorb different parts of the electromagnetic spectrum. For example, a green shirt absorbs all color wavelengths except green. A spectrometer is an instrument used for measuring what wavelengths of the spectrum are absorbed or emitted by an object. In astronomy, one method of observation is to image a distant object using a spectrometer while recording which wavelengths are absorbed. This yields an absorption profile. This profile is then checked against a database of absorption/emission profiles of thousands and elements and molecules. The database has previously been accumulated by researchers working under laboratory conditions. The researchers measure pure samples of known materials to determine their baseline emission/absorption profile. Allen and Wickramasinghe (1981), report that spectroscopic observations of a cloud of interstellar dust in front of GC IRS-7[94] yield an absorption profile not that of some minerals or elements, but closest to the bacteria Escherichia coli (E. coli) (from 2.9-3.6 µm.).[95] Figure 2 below is a re-evaluation of that finding adding 1989 data from other researchers.
Figure 2. The graph above most plainly demonstrates the methodology involved. Data points (dark points and open circles) of remotely observed infrared flux across a wavelength range are matched to a model of E.coli flux at the same wavelengths (the continuous line). The E.coli model is derived from laboratory data.[96]
Hoyle and Wickramasinghe (1988) reevaluate the 1981 findings in light of new observational data.[97] They add data from independent observations in 1989 and 1994. They find that the new data are also a very good match to the E. coli absorption spectrum. They generate a graph in which represents the absorption characteristics of the interstellar dust between stars IRS 6E and IRS 7 for 3.3-3.55 micrometer wavelengths. On this graph they superimpose a curve of the absorption characteristics of a mixture of E. coli and a virus called TMV (Tobacco Mosaic Virus). The curve of the bacteria-virus mixture absorption is a quite good match to the data points of the interstellar dust absorption.[98] Hoyle and Wickramasinghe conclude that, at a minimum, there is complex organic matter in the interstellar dust. But there is no known non-biological mechanism for how such complex organic matter could be created. So they conclude that there is biological activity that generates the complex organic matter and that in fact the organic matter whose absorption spectra we are seeing in the interstellar dust is bacteria closely related to E. coli and the Tobacco Mosaic virus.
Similar methods have demonstrated that the absorption spectrum of "galactic infrared source OH 26.5 + .6" matches that of dessicated (dried) cellulose (whose spectrum was measured under laboratory conditions.). This is contended to be a piece of evidence that biological processes are occurring or have occurred in outer space.[99]
Many researchers had thought that the spectrum of infrared radiation passing through the Trapezium nebula over the wavelengths 8-35 µm matched the spectrum that laboratory models predicted would be produced by silicon. Hoyle and Wickramasinghe find that the nebula spectrum more closely matched the spectrum that would be produced by diatoms- a water borne microorganism that incorporates silicon into various components of its structure.[100]
Wickramasinghe et al[101] conducted Earth-based spectroscopy of the coma of Halley's Comet during the 1986 flyby.[102] Over a specific range of infrared wavelengths (3-4 µm), the emissions characteristics of the comet coma are very close to the emissions characteristics of E. coli bacteria that have been heated to 320 degrees K. This is probably a reasonable temperature approximation of the temperature conditions in the coma. The Earth based observations were conducted on March 31. The European comet intercept probe Giotto measured the temperature of the outer nucleus sometime in the month of March, returning a temperature of 330 degrees K.[103] Any material in outer space is also subject to intense radiation. To better approximate the conditions in the coma, the authors subjected a sample of E. coli to a radiation dose of 1.5 megarads and then heated the sample to 320 degrees K. The infrared emissions characteristics of this irradiated sample were even closer to that of Halley's comet. The authors conclude this empirical finding is evidence that some of what is expelled from a comet is bacteria from its interior.
Based on the empirical findings, Hoyle and Wickramasinghe argue that primitive life forms extant in outer space would be frozen by the cold and dried by the absence of moisture in outer space. If this hypothesis is accurate, could the microbes survive? Is the bacteria floating outer space dead? They contend that based on what we know about the extreme survivability of terrestrial bacteria, the bacteria in outer space could be alive or dormant.[104]
Clarke et al. (1999) explain that the major obstacles to survivability of bacteria in small bodies in outer space are three: intense radiation, intense cold and absolute absence of water.[105] They note that, given the hardihood of some species of Earth bacteria, it is conceivable that some species could survive any one or even two of these factors, but the combination of all three would be insurmountable. Given the intensity of radiation, bacteria would have to be several meters below the surface of any object in order to have enough shielding to survive. Asteroids and moons of different planets may contain life at appropriate depths below the surface. The authors conclude that comets would be the most likely place where life would be found, presumably bacteria in spore form. The bacteria could be several meters under the crust of the comet, encased in ice. The factor of radiation would be absent, and since the bacteria would be encased in ice, moisture would be locked into the spores. For their part, Hoyle and Wickramasinghe suggest that bacteria could survive in the interior of an interstellar dust cloud. These bacteria would be shielded from radiation by outer part of the cloud.[106]
When Clarke et al. speak of the hardihood of bacteria, they are referring to evidence of extremophile microbes onEarth. It is worth examining some of these findings in order to understand how life could possibly survive in outer space if protected within a comet. It is well documented that there are bacteria which live in boiling water (hot springs), bacteria that eat sulfur, bacteria that live deep below the Earth in high heat and pressure and eat rocks, and organisms that live in the deep ocean around ocean vents. Vents are openings in the sea floor from which heat and various chemicals seep out from the interior of the planet. These organisms survive in almost total darkness, under great water pressure, using heat and various chemicals as their energy sources.[107] Overmann et al. (1992) found bacteria in seawater that can photo-synthesize at .0005% of the light intensity at the sea surface.[108]
One specific extremophile is Deinococcus radiodurans. This bacteria was first discovered in 1956 by a researcher working on preserving food by irradiating it. Meat that had been irradiated spoiled anyway, and the culprit turned out to be D. radiodurans. Since its discovery, it has been shown to survive radiation of up to 1.5 million rads (1500 times the dose needed to kill a human) and if frozen, it can survive up to 3 million rads. It can also survive extended periods without water (dessication).[109] Radiation in space is up to 18 million rads.[110]
When adverse conditions develop, many bacteria protect themselves by becoming dormant. "Such dormant forms are called endospores in Bacillus and Clostridium, cysts in Azotobacter, and heterocysts in some cyanobacteria. ... Endospores have no metabolic activity and exhibit extreme resistance to the lethal effects of heat, desiccation, freezing, chemicals, and radiation."[111]
Recent discoveries about the longevity of bacterial spores make more plausible the scenario that dormant bacteria could survive for eons inside small bodies in outer space. Vreeland et al. successfully cultured bacterial spores from a 250-million-year-old salt deposit in New Mexico.[112]
By what conceivable scenario might bacteria have ended up in the interior of a comet? Hoyle and Wickramasinghe provide a scenario and others provide empirical support. They state that, when a comet is formed, the core of the comet is a radioactive material that emits heat for several hundred thousand years before the heat decreases to a non-significant level. The heat from the radioactive core maintains water around the core in liquid form. Comets are 80% water and 20% other materials. Perhaps 10% of these other materials are complex organic molecules.[113] So early in the life of a comet, we have a heat source, water and nutrients (the complex organic molecules). This is all that is thought to be needed to support primitive life. [114] "Microorganisms are extremely versatile, chemically. They can live on a very simple medium with little more than water, carbon and nitrogen sources, and some simple organic compounds for their energy. Most can synthesize their need for vitamins and amino acids."[115] As the heat from the core and the supply of nutrients diminishes, the primitive life goes into a dormant state. We already know that bacteria can be revived after 250 million years. One of the main points of the landmark Gold article is that, "The chemistry of life we now know need not be the one associated with its essential origin."[116] Hoyle and Wickramasinghe hypothesize that the earliest forms of primitive could be revived after billions of years.
When a comet travels through the inner solar system, dormant bacteria are released from the nucleus into the coma and tail of the comet, where some of it reaches the Earth surface in viable condition. Once vented from the tail of a comet, any microbes would be floating in space and subject to the extremes of temperature, the vacuum and the ionizing radiation discussed by Clarke et al. These factors would render even hardy spores non-viable relatively quickly. However, once a century or more, [117] the Earth passes through a recently formed comet tail, which yields an instantaneous input of perhaps 2,000 tons of dust into the stratosphere.[118] In such conditions, the microbes would not have to survive for long in outer space before entering the atmosphere.
9.1.1 Empirical Verification
Given Hoyle and Wickramasinghe's spectral findings suggestive of the existence of microbes in space, and the reasoning of other scientists that it might indeed be possible for microbial life in the interiors of small bodies in outer space, it remains to verify the remote observations and theoretical reasoning. Most proposals focus on comets. A number of missions are currently planned that will yield relevant empirical data.
The ideal situation for investigation of comets would be for researchers to be in physical possession of a supply of material from a comet nucleus so that they can conduct a virtually unlimited amount of tests as ideas occur to them. The idea is to land on the surface of a comet, drill into the comet and retrieve a core sample several meters long. Successful return of the sample to Earth would enable scientists to study cometary material with the extensive tools available in an Earth-based laboratory. Such study would determine whether microscopic life exists in comets, provided that terrestrial contamination could be ruled out. The technology involved in a sample return mission is difficult and the author knows of no such missions that are even in the planning stages.[119]
While we wait for a nucleus sample return mission, there are several missions to comets that are either launched or near launch.
Stardust: launched 1999 Fly into the tail of a comet, collect comet dust using a material called aerogel, return samples to Earth. If the aerogel comes back with bacteria on it, that would certainly indicate that comets do harbor life, provided terrestrial contamination can be ruled out. However, Clarke et al. (1999)[120] caution that this mission could be self-sterilizing because the comet dust will strike the aerogel at 6.1 km/sec, instantaneously converting kinetic energy to extreme heat.[121]
Contour: launch 2002
Close flyby (60 miles) of a comet nucleus. Perform spectrometry similar to Earth based work done on interstellar dust by Wickramasinghe et al. in order to determine constituents of the comet.
Deep Impact: launch 2004
Launch copper projectile at nucleus of comet. The impact will excavate a deep crater in the nucleus, revealing the deep interior of the comet. Use remote sensing instruments to look inside the crater and analyze the ejecta in order determine the make-up of the comet. Observations will be made from as close as 310 miles.
Rosetta: launch 2003 Prolonged close up observation (as close as 10 miles), land on the nucleus and conduct in-situ examination of the surface of the nucleus. However, Rosetta will not dig into the interior of the comet. As Clarke et al. concluded, the microbes, if there are any, would be found in the protected interior of the comet.
Even if it is proven that bacteria and/or viruses exist in the interior of comets (step 1), it would still remain to be proven (2) that these bacteria/viruses can enter the Earth's atmosphere and (3) that they can reach the surface of the Earth as viable life forms, and (4) that they are incorporated into the biosphere, or that they started the biosphere (genesis).
9.2 Life from outer space was delivered to the early Earth so that the origin of Earthly life is extraterrestrial.
Mainstream research is pursuing the theory that organic matter and cell-like structures rained down from space upon the early Earth. (See sec. 4.2, where ample citations are provided). Where Hoyle and Wickramasinghe go further is to assert that living microorganisms rained down, and this is how life started on Earth. If the empirical research discussed in section 9.1 above establishes that comets contain dormant microorganisms, then it becomes possible that these organisms were raining down upon the Earth in relatively large quantities during the heavy bombardment from 4.5-4 billion years ago.
An essential step in validation of Hoyle and Wickramasinghe's assertion is proof that microorganisms in a dormant state could survive entry into the Earth's atmosphere. Several means have been proposed. First, if a particle is very small in size and has a high ratio of surface area to mass, the particle will be fully decelerated if it encounters its own mass of air molecules. If this occurs, the particle will not burn up in the atmosphere, rather it will drift or waft to the surface of the Earth.[122] Second, Clarke et al. (1997) state that, "It is well known that due to the process of ablation (formation of a thin, hard protective shell due to heating), competent meteoroids centimeters in size can readily traverse the atmosphere without appreciable melting of their interiors." Protected in the interior could be microorganisms. Third, if small particles enter the atmosphere at an oblique angle and low velocity relative to the Earth (if they are moving at approximately the same speed of the Earth), there will be minimal heating due to entry and survival of microorganisms in the interior of the particle is probable.[123]
Once the microorganisms have landed on the surface, how would the dormant microbes populate the Earth? This is firmly established scientific knowledge, available from an Encyclopedia:
If even one bacterium survived re-entry, given a doubling time of 1 hour, after 24 hours there would be 16,777,216 bacteria on the planet.
A significant number of scientists in space-related disciplines expect to find that microorganismic life is pervasive in the universe.[125] If so, there are three basic choices for genesis. Either life started de novo somewhere in the universe and subsequently spread to the rest of the universe, or genesis occurred on Earth and then spread to the rest of the universe, or genesis has occurred in multiple places.
9.3 Extraterrestrial microbes have continued to be delivered to Earth in the form of comet dust and interstellar dust filtering through the atmosphere to the Earth's surface.
Hoyle and Wickramasinghe contend that extraterrestrial microorganisms have continued to reach the surface during the entire existence of the planet Earth.[126] If empirically validated, the Earth would be currently and significantly an open system-not just 4 billion years ago. These primitive microbes, if found, may have similar DNA to strains of microbes on Earth because life on Earth is derived from these samples. [127] However, a high degree of genetic change and diversification may have taken place in the eons since some of these microorganisms reached this planet. (See end section 9.3.1 page 45). When extraterrestrial microbes fall onto a planet with an already thriving biosphere, they are incorporated into the ongoing ecology. "Although there would be a large fraction that perishes, of those that do not, the various environments on the Earth pick up the types best suited for replication under the conditions that locally prevail."[128]
If bacteria do exist in comets, it is a plausible hypothesis that the Earth is showered with viable extraterrestrial bacteria whenever the Earth passes through the tail of a close approach comet.[129] Sekanina and Yeomans (1989) list 36 times since 374 A.D. that a comet has passed within 16 million miles of the Earth.[130] On some of these flybys, the geometry of the approach is such that the Earth passes through the tail of the comet relatively soon after emission of the dust. On these occasions, the Earth would receive an infall of from 2,000-13,000 tons of comet dust.[131]
Empirical research is evaluating the idea. High altitude balloon experiments are conducted by a consortium of the Indian Space Research Organisation (ISRO) and the Inter-Universities Centre for Astronomy and Astrophysics in Pune, India. Wickramasinghe is affiliated with this project. In November, 2000 a balloon was sent to an altitude of 10 miles, and collected samples of living bacteria. As high as that is, it is still possible that the microbes collected could be Earthly bacteria kicked up into the stratosphere by air currents. The bacteria collected in the balloon's sampling device were, according to Wickramasinghe, "a hitherto unknown strain." "It is so different from anything we've seen before that there are only two possible explanations." The first is that "organisms have been lifted from the Earth to great heights in the skies and have somehow multiplied there and changed over time." The second is "that this is an example of primitive alien life." To eliminate the first possibility, it would be necessary to sample from a higher altitude.[132]
On January 21, 2001, the same group sent a balloon aloft which collected samples of living bacterial cells from an altitude of 25 miles. Wickramasinghe said: "There is now unambiguous evidence for the presence of clumps of living cells in air samples from as high as 41 kilometres, well above the local tropopause (16 km), above which no air from lower down would normally be transported." The finding was reported at the 2001 SPIE (International Society of Optical Engineers) conference in San Diego, California. This is a prestigious meeting of scientists from NASA, universities and government research institutes from around the world. According to reports, the findings were well-received.[133] However, a conference presentation is not a formal peer review. Publication in a refereed journal is necessary so that the methodology of the experiments can be assessed. Additionally, other scientists must be able to send up their own balloons and reproduce the finding of bacteria, and this has not yet been done.[134]
NASA's Ultra Long Duration Balloon Project would be a means of testing the Indian findings. Now in the prototype stage, this balloon is projected to be capable of attaining a minimum altitude 20 miles for 100 days. The first use of the balloon will be for research into cosmic rays. At some point in the future the balloon could be equipped to collect samples of the stratosphere in a search for bacteria.[135]
Yet the manner in which Hoyle and Wickramasinghe have pursued their research agenda is a bit troubling. Because they are so vocal in their views about extraterrestrial microbes, if the microbes turn out to be of terrestrial origin, it is a defeat for them. In fact, it is a new discovery that microbes would be present at 25 miles altitude. Many of the major discoveries in science (Penicillin, for example) were accidentally discovered in the pursuit of something else.
The Earth is significantly influenced by inputs of matter from outer space, but based on the research reviewed here, it is not an open system. Impacts of large bolides have triggered mass extinctions which have redirected the course of evolution. Kortenkamp and Dermott's theory that interplanetary dust and micrometeorites have caused some of the ice ages is also promising. These ideas alone demonstrate that the input of extraterrestrial matter has a "significant effect" on the Earth system. It is more difficult to call the Earth an "open system" because that is a term of thermodynamics. We may be able to say that the Earth was an open system at its inception (for example, an input of pre-biotic organics). However, currently the Earth system does not merit the appellation "open" because once started, system can sustain its functions without inputs of matter. These conclusions are explained in detail as follows.
The Earth is a system, hence the academic discipline Earth System Science. More accurately, the Earth is a system of systems, composed of the biosphere, atmosphere, hydrosphere and geosphere. Each of these is its own system and each acts upon the others. These systems have some of the characteristics of a life form,[136] yet the Earth is not a life form since the class of entities to which it belongs does not reproduce nor use the reproductive facilities of others (e.g. a virus). Nevertheless, it is useful briefly to consider the thermodynamics of living systems. We can build on our discussion of open systems from the introduction. The biologist and systems scientist von Bertalanffy analyzed living organisms as open systems.[137] Warm blooded animals are able to receive thermal energy (heat) from direct solar radiation (sunshine), convection (warm air), and conduction (another warm body). They can shed excess heat by perspiring, panting and increasing the flow of blood to the body surface so its warmth can be lost to the cooler ambient air. The latter process is facilitated by stretching out in order to maximize the exposed surface area. Warm blooded animals are of course open to matter in that they ingest nutrients and excrete wastes. They are self-regulating open systems which must exchange energy and matter with their environment in order to survive. Without the matter exchange the life form cannot get enough energy to maintain its state of being an organized system and it returns to disorder (entropy)- it perishes, liquefies and eventually becomes dust.
Might we consider the Earth to be a non-living, open system, such as an internal combustion engine? The engine is open to energy in that it requires a spark to begin the combustion reaction and emits heat. It is open to matter because periodic input of gasoline from an external source maintains the combustion and it excretes waste products such as carbon monoxide and nitrogen oxides. Without the exchange of matter the engine could not function.
The open system/closed system concept is thermodynamics, and proceeding on that basis, several conclusions are possible. First, we can conclude that the Earth was an open system at its inception. The theory that during the heavy bombardment complex pre-biotic organic molecules set the stage for genesis would require us to consider the Earth as an open system at its inception, since an exogenous input was necessary for the emergence of the biosphere subsystem. And without the biosphere, the atmosphere would probably be far different, because early chemosynthetic bacteria may have altered the atmosphere, making it suitable for photosynthetic life, which then further altered the atmosphere by producing oxygen.[138] Similar implications hold if the first life was of extraterrestrial origin (panspermia).
Second, we can conclude that the pre-biotic organics theory provides an opportunity to redate planet formation, and this has implications for the open system idea. The current standard theory is that the Earth was formed 4.5 billion years ago, followed by a heavy bombardment that lasted another 500 million years.[139] Yet without the delivery of the pre-biotic molecules at the tail end of the heavy bombardment, there might have been no genesis, or it would have taken very much longer. The heavy bombardment is also thought to have contributed much of the Earth's water via comet impacts. Without oceans and life, the Earth would be all but missing its biosphere, hydrosphere and have a radically different atmosphere. Perhaps we should define planet formation as complete only after the heavy bombardment.
Third, the problem for the Earth as open system argument is that after the system is in motion, it can sustain itself without exchanging matter with outer space. It is not like an internal combustion engine or a life form which require matter to sustain the process. Even if much of the research covered in this essay were to be empirically proven, the only thing that would change about the Earth would be the absence of humans (if no mass extinctions due to meteorite impacts) and a less thriving biosphere (if no 4x spike in meteoritic bombardment causing the Cambrian explosion), but a biosphere with surface life nonetheless. Does the Earth really care if dinosaurs or humans dominate the planet? Maybe it does since humans are doing a lot of damage. Even if a bolide impact into an ocean is one way the Earth emerges from ice ages, CO2 emissions from active volcanoes would probably eventually lead to a warming. Arguably, an ice age Earth still has 4 functioning subsystems. Life exists in Antarctica. Humans survived and advanced during the last ice age. And in no case would there be any outputs of matter in the form of waste products whose excretion is essential to the viability of the Earth as a functioning system. So the situation is not one of exchange, or interdependence, but of dependence where the Earth is usually on the receiving end.
Fourth, the Earth does meet the thermodynamic definition of an open system- its boundary allows matter to pass. But in some sense it does so in a trivial way. Imagine that a 1 micron particle of interplanetary dust burns up while entering the atmosphere. The particle has kinetic energy as it enters the atmosphere at high speed. The kinetic energy is turned into heat energy by the friction between the particle and air molecules. The heating of the air molecules is a minute gain in energy to the Earth system.
Yet the individuals quoted in the introduction are on to something. They seem to envision a universe of significantly open, interdependent systems within systems. It is an enchanting thought and this author was of like mind until the last stages of preparation of this manuscript. The current scientific evidence doesn't quite support the view. Yet the open system perspective remains a legitimate source of creative hypotheses, which are the engine of scientific advancement provided they are subject to rigorous standards of proof. Perhaps one young researcher will read this manuscript and notice something in his or her research that would otherwise have gone unnoticed.
The key to sensing objects with radar is the radar cross section (RCS). This is the size of the scanned object as perceived by the radar. It is dependent upon the size, density, type of material, smoothness of surface of the object, and other factors. For example, stealth technology is about reducing the amount of radar waves reflected back to the receiver so that an airplane appears to be the size of a pebble on the radar scope. For the altitude of 1000-3000 km, the naval radar can detect objects with a radar cross section as small as .1 meter2. For comparison, this is the same radar cross section as a locust.[140]
Knowles et al. calculate the average radar section of a small comet to be .4 m2. This figure is based upon careful review of the theoretical characteristics of small comets, as explained in various articles by proponents of the small comet hypothesis. Small comets range in physical diameter from 5 to 20 meters, but because they are porous, of low density, and composed mainly of water snow, they have very small radar cross sections.
In various articles, Frank and Sigwarth state that small comets break up by an altitude of 1000 km (Frank and Sigwarth, 1988, 1993), but they also report detecting evidence of small comets at 10,000 km. (Frank and Sigwarth, 1997). Accordingly, Knowles et al. run two searches of the data. First, they ask whether, any small comets were detected at 1000-3000 km altitude, where the radar has a .1 meter2 sensitivity. Then they ask whether any small comets were detected between 3000-20,000 km, where the average sensitivity of the radar is .5 meter2. Again, Knowles et al. calculate the average radar section of a small comet to be .4 m2.
In the lower altitudes (1000-3000 km) the radar sensitivity is far below that of the average cross section of a small comet, so if there are any small comets, a good portion should be detected. In the higher altitudes of 3000-20,000 km, the radar would not be sensitive to the average small comet, but many of the larger diameter comets would be observable by the radar. However, the result of the radar search was that absolutely no small comets were detected.
During the approximately 1 month of searching with the radar, some 12,000 unidentified targets were observed. Of these, none fit the theoretical characteristics of small comets. 50 were signal noise, and the rest were either new satellites, moving too slowly to be small comets or were in gravitationally bound orbits (not unbound infalling objects).
Frank and Sigwarth reply "Comment on 'A search for small comets with the Naval Space Command Radar'"
In a later issue of the journal in which Knowles et al. was published, Frank and Sigwarth were given space to respond to the findings.[141] They argue that the whole point is that comets are hard to detect, and the Naval Space Command radar is simply not one of the instruments that can detect them. Their criticisms shall here be evaluated point by point.
In § 2 of the their reply, Frank and Sigwarth claim that Knowles et al. use a higher dust content for the small comets than that documented by Frank and Sigwarth. Frank and Sigwarth assert that using a higher dust content raises the predicted radar cross section (RCS) of the small comets the radar is searching for. This way, Knowles et al. can say that the naval radar has the capability of seeing them, yet they do not show up, so they do not exist.
This contention by Frank and Sigwarth is apparently incorrect. In the Knowles et al. article, the authors do run some calculations of what the small comet RCS would be if they had 10% dust throughout the comet.[142] The RCS would be much larger. But they expressly state that these calculations are for comparison purposes only. Knowles et al. specifically do not use the 10% dust RCS predictions in assessing whether small comets were detected.
In § 3, Frank and Sigwarth contend that "The model of the comets used by Knowles et. al employs the small density for the water snow, .02 g/cm3, in order to yield the largest radar cross section." By calculating that small comets have a relatively large RCS, Knowles et al. would then be able to report that the comets should have been visible to the radar, but were not detected, so they do not exist. Alternatively, if the calculations were to show that the comets should have a very small RCS, then it would be easier for Frank and Sigwarth to argue that the comets are simply not detectable by the naval radar and that is why they were not detected.
This contention by Frank and Sigwarth is false. Knowles et al. expressly state that raising the density raises the cross section (and by implication, using the lower density of .02 lowers the cross section): "The above computations were made with the minimum snow density given by Frank and Sigwarth (1993). Raising the snow density to .1 g/cm3 (their upper limit) approximately doubles the RCSs...."[143] Knowles et al. use the lowest density, yielding the lowest predicted cross section for the small comets. This lowers the bar that the small comet theory needs to overcome. Because they have such a small predicted RCS, the expected frequency of detection is lower, so fewer small comets need be identified in order to validate the theory.
In § 3, Frank and Sigwarth object to the assumption that small comets are perfect spheres. Knowles et al. had made this assumption "for computational ease."[144] It is indeed a fact that the RCS of a dielectric[145] sphere exhibits extreme oscillations.[146] About half the time, the sphere has a large cross section, but the other half of the time the cross section drops precipitously, sometimes to near zero. This characteristic would make it more difficult to observe small comets by radar, and would go some distance towards explaining why the naval radar did not detect any. Frank and Sigwarth assert that in nature, small comets are probably lumpy spheres, so that it would have been better to model them as an ensemble of spheres of diameter x.
This objection has merit, but Knowles et al. demonstrate that it did not affect the results. In the original article, Knowles et al. noted that their model did yield large oscillations in the predicted RCS of small comets.[147] There they ascribed the oscillations to other sources, but they did expressly note their existence and apparently took the existence of oscillations into account in calculating the expected detection frequency of small comets. Furthermore, in their reply to Frank and Sigwarth's commentary, Knowles et al. calculate the RCS for small comets as an ensemble of spheres. The result is the same type of oscillations as with the perfect sphere model. Knowles et al. based their computations on a model of the radar characteristics of objects that are an ensemble of spheres. The model was developed by independent third party researchers and tested at a highly-regarded radar research facility at the University of Florida, where it was found to yield accurate predictions of RCS. (p. 22,610).
In § 4, of their commentary, Frank and Sigwarth argue that Knowles et al.'s assumption of a perfect sphere shape for small comets has the effect of raising the predicted RCS- thus lowering the bar for disproving the existence ("If they have such a big RCS, why didn't we see them?"). They again state that Knowles et al. should have modeled small comets as ensembles of smaller spheres. They say, "Note that small comets which are characterized by surfaces with smaller bosses than 5-meter diameter will have small RCSs relative to those shown in Figure 2." (p. 22,606). Modeled this way, small comets would have a small predicted RCS, so that the predicted detection rate would be very low.
It takes some explanation to understand Frank and Sigwarth's terminology. A "boss" is a feature of medieval European cathedral architecture. It was a decorative hemisphere placed over the intersection of a structural joint in order to hide the structural components. They are stating that small comets are lumpy spheres, and that the structure is a core with hemispheres clumped around it.
The problem with Frank and Sigwarth's quoted assertion is that it is inconsistent with their own figure 2 on the very same page (p. 22,606). This figure shows that small comets with diameters 7 meters or larger should be detectable by the naval radar. A 7 meter comet is unlikely to have bosses of 5 meters each. Therefore surfaces with smaller bosses than 5 meters are already included in their figure 2 and figure 2 says that the naval radar should be able to detect the typical small comet.
In § 5, Frank and Sigwarth claim that the size distribution of small comets used by Knowles et al. is skewed towards a search for larger size small comets than actually exist. They state that the typical diameter of a small comet is 8 meters indiameter. Yet according to Frank and Sigwarth's own graph (fig. 2, p. 22,606), a comet 8 meters in diameter has a RCS above .1 meters2 and thus would have been detectable by the naval radar within the altitude of 1000-3000 km.
Knowles et al. used perhaps the most appropriate radar system on Earth to search for small comets and found none. Frank and Sigwarth were given the opportunity to critique the research, but none of their objections appears valid. The results of the Naval Space Command radar observations seem to be strong empirical evidence against the existence of small comets.
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[1] Astronomy, astrophysics, astrobiology, geology and geophysics, to name a few.
[2] Pasachoff and Kutner, University Astronomy (Philadelphia: W.B. Saunders Co., 1978), 517.
[3] David M. Raup, The Nemesis Affair, (New York: W.W. Norton & Co., 1986), 34. (italics added)
[4] Art Sussman, Dr. Art's Guide to Planet Earth, (White River Junction, Vermont: Chelsea Green Publishing Co., 2000).
[5] Csaba H. Detre, ed. Terrestrial and Cosmic Spherules, (Budapest: Akademiai Kiado, 2000): introduction.
[6] James Grier Miller and Jessie L. Miller, "The Earth as a System," paper presented on The First International Electronic Seminar on Wholeness, 2000. At http://www.newciv.org/ISSS_Primer/seminar.html.
[7] Jefferson W. Tester and Michael Modell, Thermodynamics and It's Applications 3rd Edition, (Saddle River, N.J: Prentice Hall, 1997).
[8] Thomas Gold, "The Deep, Hot Biosphere," Proceedings of the. National Academy of. Sciences, 89 (1992): 6045-6049.
[9] Richard A. Lutz and Michael J. Kennish, Reviews of Geophysics, vol. 31, (Aug 1993): 210.
[10] The hypothesis that life did not originate on Earth, but was transported through space to Earth by natural processes.
[11] See Michael W. Friedlander, Cosmic Rays, (Cambridge: Harvard University Press, 2000).
[12] C.S Detre et al., The Paleozoic Came to End By the Biggest Train of Disasters Known in the Earth's History, in Csaba H. Detre, ed. Terrestrial and Cosmic Spherules, (Budapest: Akademiai Kiado, 2000)
[13] M.R. Rampino, B.M. Haggerty, "Extraterrestrial impacts and mass extinctions of life," in: T. Gehrels ed., "Hazards due to comets and asteroids," (Tucson: University of Arizona, 1994); M.R. Rampino, B.M. Haggerty,. "Impact crises and mass extinctions: a working hypothesis," in: G. Ryder, D. Fastovsky, S. Gartner eds., "Special Paper 307: The cretaceous-tertiary event and other catastrophes in Earth history," (Boulder, CO: Geological Society of America, 1996); D. Raup, J. Sepkoski, Periodicity of extinctions in the geologic past. Proceedings of the National Academy of Science U.S.A. (1984): 81, 801-805.
[14] Luann Becker et al., "Impact Event at the Permian-Triassic Boundary: Evidence from Extraterrestrial Noble Gases in Fullerenes", Science 291 (2001): 1530-1533. NASA Ames Research Center, News, "Asteroid or Comet Caused Earth's Largest Mass Extinction," September 6, 2001; NASA Astrobiology Institute, Astrobiology News, "Apocalypse Then," February 26, 2001.
[15] The K-T crater at Chicxulub, Mexico is 150 km in diameter. Natural Resources of Canada, Regional Geophysics Section, 2000. List of terrestrial impact structures available online at http://gdcinfo.agg.emr.ca/crater/crater_table_e.html.
[16] H. Koshiishi, et al., "New Information on Craters from Remote Sensing Data," in Csaba H. Detre, Terrestrial and Cosmic Spherules, (Budapest: Akademiai Kiado, 2000). This group has found a corresponding crater for the Triassic-Jurassic boundary (144 million years BP.).
[17] A concentration of dormant comets beginning near Neptune and stretching beyond the planets.
[18] E.M. Leitch, G. Vasisht, "Mass Extinctions and the Sun's Encounters with Spiral Arms, New Astronomy 3 (1998), 51-56; S.V.M. Clube and W.M. Napier, "Mankind's future; an astronomical view; comets ice ages and catastrophes," Interdisciplinary Science Reviews, vol 11, no. 3 (1986): 236-246
[19] A concentration of dormant comets beyond the Kuiper Belt- about .15-1.5 light years from the sun.
[20] David M. Raup, The Nemesis Affair, (New York: W.W. Norton & Company, 1986); and see Professor Richard A. Muller's websiste: http://muller.lbl.gov/pages/lbl-nem.htm.
[21] Gladman, B.J., et al. 1996., "The exchange of impact ejecta between terrestrial planets," Science 271(March 8):1387; M.K. Wallis and N.C. Wickramasinghe, "Role of Terrestrial Cratering Events in Dispersing Life in the Solar System," Earth and Planetary Science Letters 130 (1995): 69-73.
[22] Ron Cowen, "Interplanetary Odyssey: Can a rock journeying from Mars to Earth carry life?" Science News, 9/28/96
[23] Gold, "The Deep, Hot Biosphere," supra note 8.
[24] see sections 9.1 and 9.2 this paper
[25] Ibid.
[26]M. Genge, "Micrometeorites: little rocks with a big message," Geology Today 14 (1998): 177-181.
[27] Bernstein, Sandford and Allamandola, "Life's Far-Flung Raw Materials," Scientific American, July 1999; Michael A. Seeds, Astronomy, (Belmont, CA: Wadsworth, 1999), 113 and 200-213.
[28] Genge, 177; S.J. Kortenkamp and S.F. Dermott, "A 100,000 Year Periodicity in the Accretion Rate of Interplanetary Dust," Science 280 (1998), 874-876; M. Maurette, C. Jéhanno, E. Robin, C. Hammer, "Characteristics and mass distribution of extraterrestrial dust from the greenland ice cap," Nature 328 (1987), 699-702; Ellen J. Zeman, "Complex Organic Molecules Found in Interplanetary Dust Particles," Physics Today, March 1994.
[29] Genge, 177.
[30] Klaus Scherer and Hans-Jörg Fahr "Drag forces in the near and distant solar system" Earth Planets Space, Vol. 50 (Nos. 6, 7), pp. 545-550, 1998.
[31] Poynting-Robertson drag is the effect of solar photons on dust particles' trajectories. While the speed of light is fast, objects moving around the sun will have more light hit the leading edge than the trailing edge. This slows the object down, decreasing the distance it is from the sun. For large objects like the Earth, the drag is minimal; however, for dust and small objects, they will be pulled significantly to the Sun. By analogy, as you drive a car in a rainstorm, your front windshield may hit more rain drops than the back windshield. This is because you are moving forward into the raindrops. The same thing happens to objects as they move around the Sun. Description from http://home.att.net/~eepalmer/Build/build_insolation.html.
See, Genge, p. 178, D.B. Patterson,K.A. Farley, B. Schmitz, "Preservation of extraterrestrial 3He in 480-Ma-old marine limestones," Earth and Planetary Science Letters 163 (1998): 315-325, at 315; N.N. Gor'kavyi, L.M. Ozernoy, J.C. Mather, T. Taidakova, "Quasi-stationary States of Dust Flows Under Poynting-Robertson Drag," Astrophysical Journal 488 (1997): 268-276.
[32] The solar wind is a flux of atomic particles ejected from the sun, traveling though the solar system at speed of some 400 km/sec. Klaus Scherer and Hans-Jörg Fahr "Drag forces in the near and distant solar system" Earth Planets Space, Vol. 50 (Nos. 6, 7), pp. 545-550, 1998.
[33] S. G. Love, D.E. Brownlee, "A direct measurement of the terrestrial mass accretion rate of cosmic dust," Science 262, (1993): 550-553. The authors measured small impact craters on the Long Duration Exposure Facility. This facility was in orbit from April 1984-January 1990. The 5.5 year snapshot is a useful datapoint but perhaps not a definitive statement of the accretion rate over geologic time. See also: Rietmeijer, F.J.M., 1998. Interplanetary Dust, in A.S. Marfunin, ed., Mineral Matter in Space, Mantle, Ocean Floor, Biosphere, Environmental Management, and Jewelry, (Berlin: Springer-Verlag, 1998), 29. M. Genge, "Micrometeorites: little rocks with a big message," Geology Today 14 (1998): 177-181.
[34] S.J. Kortenkamp and S.F. Dermott, "A 100,000 Year Periodicity in the Accretion Rate of Interplanetary Dust," Science 280 (1998), 874-876. (Section 4.1, p. 15)
[35]1 micrometer (micron) = 1 x 10-6 meter; internet description of research at Institute of Meteoritics at University of New Mexico "Circumstellar and Interstellar Dust in Primitive Solar System Materials" project (10).
[36]1 Å = 1 angstrom = 10-10 meters. Genge, 180; Marfunin, ed., 29; Ellen J. Zeman, "Complex Organic Molecules Found in Interplanetary Dust Particles," Physics Today, March 1994, at 17.
[37] Zeman, "Complex Organic Molecules Found in Interplanetary Dust Particles," at 17; S.J. Clemett, C.R. Maechling, R.N. Zare, P.D. Swan, R.M. Walker, "Identification of complex aromatic molecules in individual interplanetary dust particles," Science 262 (1993): 721-725.
[38] Genge, p. 178.
[39] Personal Correspondence, Dr. George J. Flynn, Professor of Physics, SUNY Plattsburg: 2/22/00 and 2/25/00.
[40] Bernstein et. al, "Life's Far Flung Raw Materials," cite Sandford (without giving a specific citation) as having analyzed IPD collected in the stratosphere and found them to contain as much as 50% organic carbon. They use 10% organic carbon as a low estimate for average carbon content. Meanwhile Maurette (1998, p. 386) found that his Antarctic Micrometeorites contained about 7% organic carbon. The figure of up to 90% is given in G.J. Flynn, L.P. Keller, C. Jacobsen, S. Wirick, M.A. Miller, "Organic carbon in interplanetary dust particles," Bioastronomy 1999 Conference Procedings.
[41] Genge, 178; Zeman, Complex Organic Molecules Found in Interplanetary Dust Particles, at 18, Patterson, Farley, Schmitz, Preservation of Extraterrestrial 3He, 315-325.
[42] Genge, 177, 179; M. Maurette, "Carbonaceous micrometeorites and the origins of life," Origins of Life and Evolution of the Biosphere 28 (1998), 385-412 at 385, 388.
[43] Maurette, p. 386.
[44] 50% survival rate of the 40,000 ton rate detected by Love and Brownlee.
[45] The solar system and planets were created around 4.5 billion years ago. At that time, there was a large mass of extra material floating around which rained down upon the Earth for some 500 million years. This period is known as the heavy bombardment. Over the billions of years subsequent the amount of free flying material in the solar system has been drastically culled due to collisions with planets and the sun. For an article proposing a method of detecting the rate of IPD accretion as long as 480 million years ago, see Patterson, Farley, Schmitz, Preservation of Extraterrestrial 3He.
[46] Robert C. Weast, Ph.D., ed., CRC Handbook of Chemistry and Physics, 62nd Edition, 1981-1982.
[47] Ibid
[48] David A. Vallado, Fundamentals of Astrodynamics and Applications, (New York: McGraw-Hill, 1997), 76, 177, 181.
[49] Vallado, Fundamentals of Astrodynamics and Applications; http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html; http://aa.usno.navy.mil/AA/faq/docs/seasons_orbit.html
[50] J.D. Hays, J. Imbrie, N.J. Shackleton, "Variations In Earth's Orbit-Pacemaker of Ice Ages," Science 194 (1976): 1121-1132.
[51] David Deming, "On the Possible Influence of Extraterrestrial Volatiles on Earth's Climate and the Origin of the Oceans," Palaeogeography, Palaeoclimatology, Palaeoecology 146 (1999), at 35 and 47-48.
[52] Ibid. An example of a positive feedback effect is that a .15 degree warming would melt some of the glaciers, which would increase the amount of water vapor in the atmosphere. Since water vapor is a greenhouse gas, it increases the global average temperature, which melts more glaciers, which leads to more water vapor, which leads in turn to warmer temperatures. Less glacial cover means the Earth has a lower albedo, which further increases warming. We must account for how the planet does not experience a catastrophic warming due to the cumulative feedback.
[53] Paul R. Hoffman and Daniel P. Schrag, "Snowball Earth," Scientific American 282 no. 1 (1998): 68-75.
[54] R.A. Muller, G.J. MacDonald, "Glacial Cycles and Orbital Inclination," Nature 377 (1995):107-108; R.A. Muller, G.J. MacDonald, "Glacial cycles and astronomical forcing,". Science 277 (1997): 215-218; R.A. Muller, G.J. MacDonald, Ice Ages and Astronomical Causes: data, spectral analysis, and mechanisms (Praxis, 2000).
[55] Orbital inclination of the Earth for the period 0-3 million years ago, as calculated by T. R. Quinn, S. Tremaine, and M. Duncan, Astronomical Journal, 101 (1991): 2287-2305.
[56] The mean plane of the orbital inclination about the sun is known as the ecliptic
[57] Deming, 34. Solar insolation is the amount of the sun's area reaching a unit area of the Earth's surface. It is a function of four main factors: (1) the solar constant- the amount of energy that at in a unit of time reaches a unit planar surface area outside the Earth's atmosphere; (2) the Sun's elevation in the sky; (3) the amount of solar radiation returned to space at the Earth-atmosphere boundary; (4) the amount of solar radiation absorbed by the atmosphere; (5) the amount of solar radiation reflected back from the Earth's surface and atmosphere. Professor Rachel T. Pinker, (Meteorology, University of Maryland), Insolation, McGraw-Hill: www.accessscience.com
[58] K. Farley, "Cenozoic variations in the flux of interplanetary dust recorded by 3He in a deep-sea sediment," Nature 376 (1995): 153; K. Farley and D.B. Patterson, "A 100-kyr periodicity in the flux of extraterrestrial 3He to the sea floor," Nature 378 (1995): 600; K.A. Farley, S.G. Love, D.B. Patterson, Geochim. Cosmochim. Acta., in press.
[59] Muller and MacDonald, 1995, 1997.
[60] Aerosol cooling is a decrease in solar insolation due to blockage of sunlight by dust in the atmosphere. One example of aerosol cooling is that a massive volcanic eruption can cool the Earth's climate for a time due to the amount of dust it throws into the atmosphere.
[61] Farley quoted in Science News 152 (October 4, 1997): 220-221
[62] S.J. Kortenkamp and S.F. Dermott, "A 100,000 Year Periodicity in the Accretion Rate of Interplanetary Dust," Science 280 (1998), 874-876.
[63] S. Kortenmamp, "Amid the Swirl of Interplanetary Dust," Mercury, vol. 27 no. 6 (Nov/Dec 1998), at p. 8 of 11 in the electronic edition (OCLC).
[64] The Love and Brownlee measurement of the rate of cosmic dust accretion (see footnote 14) was made on the Long Duration Exposure Facility, which was in orbit from April 1984-January 1990. During this period the Earth was in the circular phase of the eccentricity cycle, so that the Earth was near the high point of the dust accretion rate.
[65] S. Kortenmamp, "Amid the Swirl of Interplanetary Dust."
[66] So the asteroid collision would lead to an increase in MM and IPD hitting the Earth over three orders of magnitude higher than the Love and Brownlee estimate discussed infra, note 7.
[67] Kortenkamp and Dermott cite M.R. Rampino, S. Self, R.B. Strothers, "Volcanic Winters," Annual Review of Earth and Planetary Sciences," 16 (1988): 73. A similar figure is given by R.F. Pueschel, "Atmospheric Aerosols," in Singh, ed. Composition, Chemistry and Climate of the Atmosphere, (New York: Van Nostrand Reinhold, 1995). Pueschel states that volcanism contributes aerosol emissions of 25-550 x 109 kg/year.
[68] Cooling by volcanic aerosol is caused by particles with high sulfur content. (E-mail correspondence, Dr. Robert Ellingson, se footnote 41). It appears that very few if any asteroids have such a composition.
[69] This section draws on e-mail correspondence with Dr. Stephen J. Kortenkamp, Planetary Science Institute and Lunary & Planetary Lab, University of Arizona.
[70] Suggested in conversation by Robert G. Ellingson, Professor of Meteorology, University of Maryland, College Park.
[71] C. Donald Ahrens, Meteorology Today: An Introduction to Weather, Climate and the Environment, (St. Paul, Minn.: West Publishing Company, 1982).
[72] Stephen H. Schneider, Can We Forecast Climate Future without Knowing Climate Past?, in W.G. Ernst, ed., Earth Systems: Processes and Issues, (Cambridge: Cambridge University Press, 2000).
[73] Schneider, Can We Predict Climate Change Accurately?, Ibid.
[74] Thiemens of the University of California at San Diego quoted in Environmental News Network (www.enn.com), Earth's Ancient Atmosphere Trapped in Rocks, July 13, 2000.
[75] S.A. Sandford, L.J. Allamandola, M.P. Bernstein, "Organic Chemistry: from the Interstellar Medium to the Solar System," in C.E. Woodward, J.M. Shull, and H.A. Thronson, eds. ORIGINS, ASP Conference Series, vol. 148, (1998). M.P Bernstein, J.P. Dworkin, S.A. Sandford, L.J. Allamondola, "Ultraviolet Irradiation of Naphthalene in H2O ice: Implications for Meteorites and Biogenesis," Meteoritics & Planetary Science, vol. 36, no. 3: 351-8. G. Cooper et al., "Carbonaceous meteorites as a source of sugar related organic compounds for the early Earth," Nature, vol. 414, 879-883. M. Maurette, "Carbonaceous Micrometeorites and the Origin of Life," Origins of Life and Evolution of the Biosphere, vol 28, n4-6, (1998), 385-412. A. Delsemme, Our Cosmic Origins- From the Big Bang to the Emergence of Life and Intelligence, (Cambridge University Press: 1998). R. Cowen, "Life's Housing May Come from Space," Science News, 2/3/2001. J. Gorman, "Cosmic Chemistry Gets Creative," Science News, 5/19/2001.
[76] S.J. Mojzsis, A.P. Nutman, C.R.L. Friend, G. Arrhenius, K.D. McKeegan, T.M. Harrison, Nature 384 (1996): 55-59; Additionally, researchers have found chemical traces in rocks from 3.8 GA which they believe are definitely by products of biological processes. See NASA news release 96-230, Nov. 6, 1996. "Life on Earth began at Least 3.85 billion years ago."
[77] S.L. Miller, "A Production of Amino Acids Under Possible Primitive Earth Conditions," Science 117 (1953): 528-529.
[78] 1 angstrom = 1 x 10-10 meter.
[79] E-mail correspondence with Scott Sandford January 2000, M. Maurette, C. Hammer, D.E. Brownlee, N. Reeh, H.H. Thomsen, "Placers of Cosmic Dust in the Blue Ice Lakes of Greenland," Science 233 (1986): 869-872; M. Maurette, C. Jehanno, E. Robin, C. Hammer, "Characteristics and mass distribution of extraterrestrial dust from the Greenland ice cap," Nature 328 (1987): 699-702; M. Maurette, "Carbonaceous Micrometeorites and the Origins of Life," Origins of Life and Evolution of the Biosphere 28 (1998): 385-412.
[80] Personal conversation with Dr. Douglas E. Gill (ecologist/biologist) UMD, November 2000.
[81] Cambrian period: 540-505 million years ago. The fossil record shows a sudden flowering in the diversity and complexity of life on Earth.
[82] T.S. Culler, T.A. Becker, R.A. Muller, P.R. Renne, Lunar Impact History from 40Ar/39Ar Dating of Glass Spherules. Science 287 (2000): 1785-1788; G. Ryder, "Glass Beads Tell a Tale of Lunar Bombardment," Science 287 (2000): 1768-1769.
[83] http://sdrc.lib.uiowa.edu/preslectures/frank99/index.html. This site contains The 1999 University of Iowa Presidential Lecture: "Small Comets and Our Origins: The Ecstasy and Agony of the Scientific Debate," delivered February 21, 1999. If this URL is no longer functioning, see the book : L. A. Frank, Patrick Huyghe, The Big Splash, (New York: Birch Lane, 1990), (Reprinted by Avon, New York, 1991) or the article L. A. Frank and J. B. Sigwarth, Reviews ofGeophysics, 31, 1-28, 1993.
[84] R.L. Mutel and J.D. Fix, "An Optical Search for Small Comets," Journal of Geophysical Research, vol. 105, no. A11, pages 24.907-24.915.
[85] L.A. Frank and J.B. Sigwarth, "Detection of Small Comets with a Ground-Based Telescope," Journal of Geophysical Research, vol. 106, no. A3, pages 3665-3683.
[86] S. Knowles, R.R. Meier, B.A.S. Gustafson, F.J. Giovane, "A Search for Small Comets with the Naval Space Command Radar," Journal of Geophysical Research, vol. 104 no. A6, (June 1999): 12,637-43.
[87] David Deming, "On the Possible Influence of Extraterrestrial Volatiles on Earth's Climate and the Origin of the Oceans," Palaeogeography, Palaeoclimatology, Palaeoecology 146 (1999): 33-51
[88] Fred Hoyle and Chandra Wickramasinghe, "Cometary Impacts and Ice Ages," Astrophysics and Space Science 275 (2001): 367-376.
[89] Paul R. Hoffman and Daniel P. Schrag, "Snowball Earth," Scientific American 282 no. 1 (1998): 68-75.
[90] R.B. Hoover, ed., "Proceedings of SPIE: Instruments, Methods and Missions for Astrobiology II," International Society for Optical Engineering, 1999.
[91] Manfred Schidlowski, Life on the early Earth: Bridgehead from Cosmos or autochthonous phenomenon?, in K. Gopalan, et al., eds., From Mantle to Meteorites, (Bangalore: Indian Academy of Sciences, 1990).
[92] R.B. Hoover, Meteorites, Microfossils and Exobiology, NASA/TM-97-207366. 1997. Report NAS 1.26:207366.
[93] See, A. Yu. Rozanov, R.B. Hoover, "Biomorphs in Carbonaceous Chondrites," Conference Paper 1278.pdf, Lunar and Planetary Science XXXII (2001); A. Yu. Rozanov, R.B. Hoover, "Biomorphic Structures in Mighei Carbonaceous Chondrite," Conference on Instruments, Methods, and Missions for Astrobiology II, SPIE Vol. 3755, pp. 120-127.
[94] GC stands for General Catalogue. IRS stands for International Reference Star. These are means of identifying deep space objects.
[95] D.A. Allen and D.T. Wickramasinghe, "Diffuse Interstellar Absorption Bands Between 2.9 and 4.0 :m," Nature 294 (1981): 240-241.
[96] Fred Hoyle and Chandra Wickramasinghe, "Infrared Evidence for Panspermia: An Update," Astrophysics and Space Science 268 (1999): 229-245, fig. 8 at 239.
[97] Hoyle and Wickramasinghe, "Infrared Evidence for Panspermia: An Update."
[98] Ibid, 243.
[99] F. Hoyle and N.C. Wickramasinghe, "Comets- A Vehicle for Panspermia," Astrophysics and Space Science, 268 (1999): 333-341. (Originally published 1981).
[100] F. Hoyle and N.C. Wickramasinghe, Infrared Evidence For Panspermia: An Update, supra.
[101] D.T. Wickramasinghe, F. Hoyle, N.C. Wickramasinghe, S. Al-Mufti, A Model of the 2-4 mm Spectrum of Comet Halley, Astrophysics and Space Science 268 (1999): 349-353.
[102] The nucleus of a comet is from 1 to 40 kilometers in diameter and is composed of 80% water and 20% other materials. In the comets that have been closely observed, the nucleus seems to be encased in a hard, black non-reflective carbonaceous material. In the dormant state, comets are very hard to observe since they are essentially encased in black carbon. But forces of gravity from the gas giant planets and nearby stars send a few comets at a time careening out of their resting places in the outer solar system towards the sun. Once a comet passes close enough to the sun, the heat of the sun creates cracks in the outer shell, and begins to vaporize the water inside, which then flies out of the nucleus in vapor form, bringing large quantities of gas and dust particles with it. The gas and dust particles become the coma and tail of the comet. J.K. Beatty, C.C. Petersen, A. Chaiken, eds., The New Solar System, 4th ed., (Sky Publishing Co. and Cambridge University Press: 1999), chapter 4; J.C. Brandt; R. Burnham, Great Comets, (Cambridge University Press: 2000), 96-98.
[103] What Have We Learned About Halley's Comet?, Astronomical Society of the Pacific, on the internet at http://www.aspsky.org/education/tnl/06/06.html. See subsection "Composition and Temperature."
[104] F. Hoyle and N.C. Wickramasinghe, "On the Nature of Interstellar Grains," Astrophysics and Space Science 268 (1999): 249-262.
[105] Clarke et al., "Surival of Life on Asteroids, Comets and other Small Bodies," Origins of Life and the Evolution of the Biosphere 29, no. 5 (1999): 521-545.
[106] F. Hoyle and N.C. Wickramasinghe, "Comets- A Vehicle for Panspermia," Astrophysics and Space Science, 268 (1999): 333-341. (Originally published 1981).
[107] Entire paragraph: Thomas Gold, "The Deep, Hot Biosphere," Proceedings of the. National Academy of. Sciences, 89 (1992): 6045-6049. See also: Encyclopedia Britannica entry "Life in Extreme Environments."
[108]J. Overmann, H. Cypionka, N. Pfenning, An extremely low-light-adapted phototrophic sulfur bacterium from the Black Sea, Limnology and Oceanography, vol. 37, no. 1, (1992): 150-155.
[109] Science News, Vol. 154, No. 24, December 12, 1998, 376.
[110] Clarke et al., 1999.
[111] Encyclopedia Britannica entry on "Bacteria".
[112] New Scientist, 21 October 2000, p 12; Science News, Vol. 155, No. 24 (June 12, 1999).
[113] J.K. Beatty, C.C. Petersen, A. Chaiken, eds., The New Solar System, 4th ed., (Sky Publishing Co. and Cambridge University Press: 1999), chapter 4; J.C. Brandt; R. Burnham, Great Comets, (Cambridge University Press: 2000), 96-98.
[114] Gold, "The Deep, Hot Biosphere," supra.
[115] NASA Astrobiologist Gerald Soffen (Ph.D., Biology) keynote address SPIE 1999, "Life is Everywhere?" in Conference on Instruments, Methods, and Missions for Astrobiology II, (SPIE Vol. 37552): 2-7 at 6.
[116] Gold, "The Deep, Hot Biosphere," at 6049.
[117] Z. Sekanina and D.K. Yeomans, "Close Encounters Collisions of Comets with the Earth," The Astronomical Journal 89 (1), (1984): 154-161.
[118] E-mail correspondence and personal conversation, Mike A'Hearn, Professor of Astronomy, University of Maryland, College Park, October-November, 2001. This method of calculation is informal. A typical comet vents about 1 metric ton of dust per second, and its tail has a mass of 20 x 106 tons. The tail is some 107 km long and 105 km wide, yielding a cross section of 1012 km2. The cross section of the Earth is 108 km2. Assume that the Earth passes through the tail instantaneously, since the Earth moves through space at 7.9 km/sec. The ratio of the cross sections means that the Earth will cross paths with .01% of the tail's total dust mass, or 2 metric tons. (Some data supplied by Dr. Sten Odenwald of Raytheon STX).
[119] See, J.M. Greenberg and S. Chuanjian, "Cosmic Dust in the 21st Century," Astrophysics and Space Science 269-270 (1999): 33-55.
[120] Clarke et al., "Surival of Life on Asteroids, Comets and other Small Bodies," at 540.
[121] "First Direct Chemical Analysis of Interstellar Dust," Sterne und Weltraum p 326-329, v 39, May 2000.
[122] Maurette (1998), p. 386.
[123] Clarke et al. at 539. See Genge, supra. note 25 for an illustrated discussion of ablation.
[124] Encyclopedia Britannica, "Growth of Bacterial Populations." On-line edition, 2001.
[125] G.A. Soffen (NASA), Life is Everywhere?, supra.
[126] F. Hoyle and N.C. Wickramasinghe, "Panspermia 2000," Astrophysics and Space Science 268: (1999): 1-17 at 13.
[127] Hoyle and Wickramasinghe, "Comets- A Vehicle for Panspermia," supra.
[128] Ibid.
[129] "Comets- A Vehicle for Panspermia," supra. In the remainder of this section I look at research by other scientists that appears to validate the idea.
[130] Sekanina and Yeomans found that comet impacts occur every 33 million years, while 36 close flybys have occurred in the past 1700 years. Z. Sekanina and D.K. Yeomans, "Close Encounters And Collisions of Comets With the Earth," Astronomical Journal 89 (1) (1984): 154-161. A selection of these flybys is listed on the International Astronomical Union Minor Planet Center website at http://cfa-www.harvard.edu/iau/lists/ClosestComets.html.
[131] Estimate based on footnote 10 (this paper) and the figures on the typical mass loss rate of a comet supplied by Dr. Sten Odenwald (Raytheon STX) at http://image.gsfc.nasa.gov/poetry/ask/a11175.html.
[132] "Scientists Report 'Alien' Life," November 22, 2000, wire story by United Press International carried on the Environmental News Network, (www.enn.com) and accessible by running a search on that site; "Scientists Report Possible Microbe from Space," November 24, 2000, Richard Stenger, www.cnn.com.
[133] "First Evidence Of Life Coming From Space Reported," July 30, 2001, UniSci (Daily University Science News), http://unisci.com/.; "New Evidence of Living Bacteria from Space," July 29, 2001, www.spacedaily.com/news/life-01zb.html.
[134] Space Bug: India Could Reveal It All, August 5, 2001, The Indian Express: National Network, www.indian-express.com/
[135] I. Smith, Jr., and James A. Cutts, "Floating in Space," Scientific American, (November, 1999), available on Scientific American website; website of the NASA Ultra-Long Duration Balloon Project http://www.wff.nasa.gov/~uldb/
[136] The Gaia Hypothesis
[137] Ludwig von Bertalanffy, General Systems Theory, (New York: George Braziller, 1968). Von Bertalanffy is most probably drawing on Ilya Prigogine, Etude thermodynamique des phénomènes irreversibles, (Paris: Dunod, 1947).
[138] Gold, "Deep Hot Biosphere," supra note 8.
[139] For example, see Encyclopedia Britannica 2001 (DVD-ROM version): "Physical Science: Solar System Astronomy."
[140]Merrill I. Skolnik, ed., Radar Handbook, 2nd edition, (New York: McGraw-Hill, 1990): 11.15.
[141] L.A. Frank and J.B. Sigwarth, "Comment on "A Search for small comets with the Naval Space Command Radar" by S. Knowles, et al.," Journal of Geophysical Research, vol. 104 no. A10 (1999): 22,605-22,611.
[142] Knowles et al., supra., at 12,639 column 2.
[143] Knowles et al., supra., at 12,639 col 2., 2nd full paragraph.
[144] Ibid., at 12,639.
[145] A dielectric is a material that is a non-conductor of electricity. Electricity is a flow of electrons. Dielectrics do not have many free electrons, so electricity does not flow well through them. This is relevant to its RCS because radar is an electromagnetic wave hitting the object. If the material is a good conductor, the radar wave will move electrons in the material causing the reflection of a nearly identical wave back to the radar receiver- this yields a large RCS.
[146] Skolnik, Radar Handbook, at 11.7, figure 11.4.
[147]Knowles et al., 12,639.
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