<P> Since then, the debate about the extinction of the dinosaurs and other mass extinction events has centered on whether the extinction mechanism was the asteroid impact, widespread volcanism (which occurred about the same time), or some other mechanism or combination . Most of the mechanisms suggested are catastrophic in nature . </P> <P> The observation of the Shoemaker - Levy 9 cometary collision with Jupiter illustrated that catastrophic events occur as natural events . </P> <P> One of the key differences between catastrophism and uniformitarianism is that uniformitarianism requires the assumption of vast timelines, whereas catastrophism does not . Today most geologists combine catastrophist and uniformitarianist standpoints, taking the view that Earth's history is a slow, gradual story punctuated by occasional natural catastrophic events that have affected Earth and its inhabitants . </P> <P> Modern theories also suggest that Earth's anomalously large moon was formed catastrophically . In a paper published in Icarus in 1975, William K. Hartmann and Donald R. Davis proposed that a catastrophic near - miss by a large planetesimal early in Earth's formation approximately 4.5 billion years ago blew out rocky debris, remelted Earth and formed the Moon, thus explaining the Moon's lesser density and lack of an iron core . The impact theory does have some faults; some computer simulations show the formation of a ring or multiple moons post impact, and elements are not quite the same between the earth and moon . </P>

What is the fundamental difference between uniformitarianism and catastrophism
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