The Asteroidal Impact Theory and Some Geologic Evidence for Asteroidal Impacts on Earth: A discussion of Direct and Indirect Data of Extraterrestrial Bodies and Their Motions and How They May Have Affected Earth Structures

Abstract The presence of extra-terrestrial objects such as large meteorites, asteroids and comets in random orbits in the solar system have been responsible in forming large explosive-like craters on the planets and their moons. On Earth, the smaller craters are numerous and they are the result of impacts by smaller meteorites which were still of sufficient size to survive passage through the atmosphere. The larger craters formed by larger meteors, asteroids, and comets are very infrequent in creating extra-terrestrial impact events. However in frequent they are, approximately 3,770 of them capable of producing craters in excess of 31 miles (50 km) in diameter are calculated to have impacted on Earth. As asteroid or comet, upon impacting the Earth, does leave its mark. The initial explosion forms a large crater and, if the impacting missile is extremely potent, even concentric waves may be formed outside the real crater. The very large craters may show penetrations of several miles or more into the crust or ocean floor. Since the crust of the Earth continually adjusts to aggregational and degradational loading, it is reasonable to expect that following a large impact there will be a rather rapid rebound of subcrustal material into the crater. However, because of slower regional isostatic adjustments to the unloaded crater, the crater and its surrounding area will continue to rise. The doming of the site of the crater will keep it exposed to the ravages of chemical and physical erosion. Consequently, the presence of a large cratering event will more than likely be represented only by its exposed root zone. Such a circular zone of large broken blocks devoid of volcanic rocks are designated cryptovolcanic structures. On a world-wide basis, an asteroid impact event or many relatively closely spaced events tend to be linked to local or broad extinctions of flora and fauna.