GREAT AND OUTRAGEOUS IDEAS ABOUT IMPACTS IN EARTH HISTORY – FROM EXTRAORDINARY TO ACTUALISTIC (AND BACK AGAIN)

At least since the 18^th century, there have been published scenarios of large bodies colliding or nearly colliding with the Earth during its long history. A number of these publications were reviewed, e.g., in the “Impacts Issue” of Earth Sciences History (1998, v. 17, n. 2). The professional (and public) reception of such ideas about impacts has ranged from outraged to indifferent to enthusiastic; reasons for reactions range from hegemonic to philosophic/methodologic. In the 20^th century, tolerance of impact-related ideas developed in the 1950s to 1960s, in part due to space exploration and possibly also due to mega-bomb development and testing. An interesting case study is the proposal, in three independent papers (1959-1961), that the Pacific Ocean basin originated by impact cratering.

A broader turn toward acceptance of impacts as generators not only of physical scars (“astroblemes”) but also of catastrophic changes occurred following the 1980 Science publication by Alvarez et al. regarding a terminal-Cretaceous impact. For example, the early 1980s saw publication of a book titled Catastrophes in Earth History: The New Uniformitarianism. In the 21st century, with accompanying lively to acrimonious debate, the mainstream scientific literature has entertained proposals of impact scenarios for the generation of giant sand dunes, for Younger Dryas events, and for the end-Permian mass extinction. Irrespective of the outcome of recent debates, the “new view” of the Earth as a planetary body is a “great idea” that has changed how geoscientists view Earth history.