On the possible influence of extraterrestrial volatiles on Earth's climate and the origin of the oceans

A consideration of observational and circumstantial evidence suggests that Earth may be subject to high influx rates (10(11)-10(12) kg/yr) of extraterrestrial-sourced volatile elements (carbon, hydrogen, oxygen, nitrogen) derived from comets or other primitive solar-system material. The total extraterrestrial influx rate may be four to five orders of magnitude greater than previously thought, large enough to account for today's total near-surface inventories of water and carbon. The possibility of high rates of extraterrestrial volatile-accretion suggests a new climatic paradigm wherein Earth's surface temperature is influenced by conflicting internal and external processes. A variable influx of volatile elements tends to warm the Earth, while terrestrial processes cool the planet by absorbing these gasses at a more uniform rate. Variations in extraterrestrial influx rates may explain the variation of sea level and mean global temperature over geologic time, as well as some types of climate change, the occurrence of the Pleistocene ice ages, and the asymmetry of the Phanerozoic climate record (sudden warmings, slow coolings). The extraterrestrial influx rate may also act as the pacemaker of terrestrial evolution, at times leading to mass extinctions through climatic shifts induced by changes in accretion rates with concomitant disruptions of the carbon and nitrogen cycles. 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. (C) 1999 Elsevier Science B.V. All rights reserved.