. Earth Impacts as a Threat to Civilization. University of Minnesota. Natalya S. Myers September 24,2002 In recent years we get more amp more facts showing that the present appearance of our planet was formed notonly by slow evolutionary processes, like wind erosion, but also by giganticnatural cataclysms. Geologists findevidence in sedimentary rock that extremely powerful impacts repeatedlyoccurred in the geological history of the

Earth.Since the late Paleozoic period i.e. for the last250 million years there are noticeable gaps in the evolution of livingorganisms. Paleontologists established that around 247, 220 and 65 millionyears ago about 95 of all life on Earth perished. Most recently, for example,the gigantic dinosaurs died out. It is obvious that such extinctions ofterrestrial living organisms are the complex result of many processes. Sharp climate variations, ice formations,fluctuation of the level of oceans, decreases of concentration

of oxygen in thewaters of seas and oceans, and different extraterrestrial circumstances all playeda part. However, to name the most important reason, was extremely difficult todiscover.Scientists assumed that at that time theEarth underwent bombardment by large asteroids. Space and aerial photography,executed in slanting solar illumination, revealed likely asteroid impact sites.Studies at the sites confirmed the Earth s encounters with celestial bodies.

Impact with an asteroid about 10 kilometers indiameter is thought to have caused mass death of dinosaurs. If the impact had arrived on the land, itwould have sharply cooled, but if over the surface of ocean or sea, then watervapor would have produced a greenhouse effect and begun to warm the Eartheverywhere. The Earth may also have witnessed hot nitric acid rains, whoseaction on the environment and the animal kingdom was catastrophic. Such a largeimpact could occur on