For years scientists have known of the destructive power associated with asteroids and comets. Many of these celestial bodies orbit between the planets Mars and Jupiter, and pose no threat to the Earth. However, a few asteroids orbit the sun on paths that cross the path of the Earth, and are a small threat to the earth. While scientists can only speculate as to what sort of damage an asteroid or comet would cause, we have some data that gives us a good idea. There are hundreds of meteor craters visible on the earth’s surface, from smaller than 1 km in size, to over 50 km in diameter. A small comet is believed to have impacted in the Tunguska region of Russia in 1908, causing destruction over a widespread area. We have also been able to witnessed comet Shoemaker-Levy 9 as it impacted with Jupiter, and seen the damage caused by this collision.
The extinction event at the end of the Permian is the largest extinction event to have occurred on the Earth. The fossil record shows us that 95 percent of the species that lived during the Permian died and went extinct. Unlike other extinctions, the Permian event affected both marine and terrestrial species almost equally. 80 percent of marine animals, including rugose corals, ammonoids, bryozoans, foraminifera, brachiopods, echinoderms, gastropods, trilobites, and bivalves were affected by the extinction event. So badly were these animals groups affected, that for the first few million years of the Triassic, global diversity of marine species was considerably lower than in any previous period.
70 percent of terrestrial animals were affected. These were mostly reptiles and amphibians and mammal-like reptiles including some early cynodonts (the ancestors of mammals) that went extinct. Insects are a group that many people believe to be the most adapted and most able to withstand dramatic events that will kill other species. However, even the insects were not spared from this extinction. Of 22 known orders of insects alive during the Permian, 9 orders completely disappeared, and another 10 orders were severely affected.
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