7. More on Climate

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.