- Copyright © 2003 Society of Exploration Geophysicists
Since the 1795 publication of James Hutton's Theory of the Earth with Proofs and Illustrations, uniformitarianism, sometimes simply stated as “the present is the key to the past” has been a fundamental tenet of geology. Uniformitarianism's slow geologic processes, combined with the enormous age of the Earth, have been a cornerstone of geologic thinking for the past 200 years.
On the other hand, catastrophists, such as the influential French naturalist Georges Cuvier (1769–1832), sought to explain all geologic features in a few thousand years, based partly on a literal interpretation of certain Biblical events. For example, catastrophists claimed that the enormously thick layers of sediments which Hutton said required millions of years to accumulate were laid down in the great Noachian deluge—i.e., Noah's flood.
Since then, geologists have modified the original concept of uniformitarianism by recognizing that geologic processes take place at different rates and, generally, the greater the rate, the rarer the event—for example, the concept of the “hundred-year flood” or the Gutenberg-Richter relationship (the log of the number of earthquakes greater than a certain magnitude decreases linearly with magnitude).
However, geologists have long been reluctant to call on extraterrestrial processes to explain terrestrial features; it smacked of the much-maligned deus ex machina. The pioneering work of Eugene Shoemaker (1928-1997), more than any other single person, changed this thinking. Shoemaker studied Arizona's Meteor (or Barringer) Crater, and proved that it was an impact crater, not a volcanic caldera as previously assumed (Figure 1). Until the 1960s, even the craters on the Moon were thought to be due to volcanism and not impact!
Since then, geoscientists have been looking for, and have found, other terrestrial …