In search of the historical roots of the extraterrestrial impact theory, <scp>III</scp> : Earth's revolutions versus mega‐impact periodicity after the mid‐19th‐century French geologist Félix de Boucheporn

Abstract Despite the inspiring discoveries in Laplace's System of the World (1796), the relatively little‐known contributions of the French to the theory of celestial collisions in the 19th century deserve greater recognition. In fact, only a few French impactists emerged during this time, such as Nérée Boubée (1806–1862) and Frédéric Chapel (1849–1932). In particular, Chapel, a military officer, was a farseeing pioneer of the Spaceguard and planetary defense programs proposed in 1883. However, a unique case is René‐Charles‐Félix Bertrand de Boucheporn (1811–1857), a superb field geologist, mining engineer, and natural philosopher. In 1844, he published the voluminous treatise Studies on the History of the Earth and the Reasons of the Revolutions of its Surface . Drawing on the work of two of the most eminent figures in French science, Laplace and Cuvier, Boucheporn shed new light on the fossil record, periodically disturbed by bolide mega‐impacts. His novel “system of geology” was based on the premise that repeated cometary impacts formed the equatorial mountains and marked the boundaries of geological periods by altering the biosphere as a result of climate change. Unlike Laplace, Boucheporn supposed that, despite their low density, the huge and fast cometary projectiles could alter the Earth's axis of rotation. He highlighted that, on a geological time scale, bolide impacts occurred with “a probability equivalent to certainty.” Boucheporn also conducted a refined analysis of comet impact probability, arguing that a mega‐collision would occur within 3 million years, which would coincide with the typical duration of geological periods. As recently evaluated by Şengör, Boucheporn's treatment of bolide bombardment was much more sophisticated than that of his predecessors. From a modern perspective, the extreme catastrophism proposed by Boucheporn was flawed, especially due to the substantial overestimation of comet size and speed. He advocated a model of impact‐forced punctuated evolution of the biosphere. Indicating the inevitability of an extraterrestrial impact in the geological past, he developed Laplace's laconic consideration of rare events into a meaningful hypothesis with a mathematical basis (rediscovered as a basic neocatastrophic theory by Gretener as late as 1967).