Tectonics, life, and surface processes on the Earth interact in ways that that may not seem obvious. Orographic precipitation greatly influences the development of compressional mountain ranges. Global tectonic processes have created environments which sequestered reduced carbon and allow the oxygen which we breath to accumulate in the atmosphere. Water carried to great depths in subduction zones triggers voluminous arc volcanism.
The influence of life on tectonics is more difficult to demonstrate than the influence of climate. Clearly, organisms affect mechanical and chemical erosion and determine to some extent the locations where various types of sediments are deposited. A more profound interaction where life keeps the surface conditions on the Earth compatible with its existence is the Gaia hypothesis [ Lovelock, 1989]. A weak form of the hypothesis is obviously true, life has not done anything which exterminated itself in the last three billion years. Too little is known about the interaction of tectonics, climate, and life to critically test a strong form of the hypothesis.
Surface processes, life, and tectonics are so pervasive on the Earth that geology without them is hard to envision. The neighboring planets, Mars and Venus, are thus useful examples where both tectonics and surface processes are sluggish at present. For example, Venus provides a possible extreme example of the influence of climate on tectonics in that the very high surface temperature implies the absence of the cold strong upper part of lithosphere which is present on the Earth. It has been proposed that this lithospheric weakness allowed rapid plate tectonic convection in the past so that the interior of Venus cooled more rapidly than the interior of the Earth [ Turcotte, 1993; Arkani-Hamed, 1994]. Comparative planetology and further terrestrial studies are likely to yield additional examples of climatic, biological, and tectonic interaction.
Acknowledgments. I thank Bruce Beaudoin, Manfred Strecker, David Stevenson, and an anonymous reviewer for helpful comments. This research was supported in part by the National Science Foundation grant EAR-9204708