Catastrophism is the theory that Earth has been affected by sudden, short-lived, violent events that were sometimes worldwide in scope. The Biblical story of the Great Flood is a prime example of catastrophism.
Starting in the late 18th century, scientists began looking to other paradigms for explaining geological formations. Two early proponents of the gradualist explanations for the formation of sedimentary rock and the beginnings of an understanding of the immense stretch of geological time or 'Deep time' were the 18th century 'father of geology' James Hutton and the 19th century geologist Charles Lyell.
From around 1850 to 1980, most geologists endorsed uniformitarianism and gradualism and rejected the idea that cataclysmic events such as earthquakes and volcanic eruptions played any role in the history of the earth. In part, the geologists' rejection was fostered by their impression that the catastrophists of the 19th century believed that God was directly involved in determining the history of the earth.
A 1950s proponent of catastrophism was Immanuel Velikovsky, who wrote a number of books proposing such theories as the planet Venus being a "comet" which was ejected from Jupiter 3,500 years ago and which made a number of catastrophic close passes by Earth and the other planets before settling into its current orbit. Velikovsky uses this to explain the Biblical plagues of Egypt, the Biblical reference to the "Sun standing still" for a day (explained by changes in Earth's rotation), and the sinking of Atlantis. Most scientists consider Velikovsky's theories to be pseudoscience at best, and sheer nonsense at worst.
Over the past 25 years, however, catastrophism has gained wide acceptance with regard to certain events in the distant past. The impetus for this change came from the publication of a historic paper by Walter and Luis Alvarez in 1980. This paper suggested that a 10-kilometer asteroid struck Earth 65 million years ago at the end of the Cretaceous period. The impact wiped out about 70% of all species, including the dinosaurs, leaving behind the so-called K-T boundary. In 1990, a 180-kilometer candidate crater marking the impact was identified at Chicxulub in the Yucatan Peninsula of Mexico.
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. Most of the mechanisms suggested are catastrophic in nature.
Modern theories also suggest that Earth's anomalous moon was formed catastrophically. In a paper published in Icarus in 1975, Dr William K. Hartmann and Dr Donald R. Davis proposed that a stochastic catastrophic near-miss by a large planetesimal early in the Earth's formation approximately 4.5 billion years ago blew out rocky debris, remelted the Earth and formed the Moon, thus explaining the Moon's lesser density and lack of an iron core. See giant impact theory for a more detailed description.
One of the key differences between catastrophism and uniformitarianism is that to function, uniformitarianism requires the assumption of vast time lines, whereas catastrophism can function with or without assumptions of long time lines.
Nowadays many geologists combine catastrophist and gradualist standpoints, taking the view that Earth's history is a slow, gradual story punctuated by occasional catastrophic events that have affected Earth and its inhabitants.
See also neo-catastrophism, which is an updated version of catastrophism.