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Extinctions
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Extinctions
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Mass Extinctions There have been at least 10 mass extinctions over the life of the earth.
(2) Several theories exist for the Permian-Triassiac (P-T) extinction 250 MYA: 1. Glaciation on Supercontinent of Gondwana, or on the north and south poles.
or 2. Reduction of shallow continental shelves due to the formation of the super-continent Pangea or 3. Global warming or 4. Huge volcanic lava flows from large cracks in the ground known as flood basalts in the Siberian Traps. (3) A 2001 report indicated that this event happened over a short (10,000 yrs which is short in gelogical time) period of time which supports the theory of something like an asteroid hit. (4) Cretacious-Tertiary (K-T) 65 3% marine reptiles non-avian (non-bird) dinosaurs and pterosaurs had 100% extinction from this event. The idea of a K-T impact, first put forth by Luis and Walter Alvarez more than two decades ago, came under heavy criticism from paleontologists who had always thought the creatures who perished at the end of the Mesozoic were wiped out slowly over millions of years, not in a instant's time by a fiery meteorite. * In 2004 A group of researchers led by Gerta Keller of Princeton University contends that the impact that caused the Yucatan crater occurred 300,000 years before the extinction 65 years ago. * In 2004 A group of researchers led by Gerta Keller of Princeton University contends that the impact that caused the Yucatan crater occurred 300,000 years before the extinction 65 years ago.
The latest fossil evidence argues that the mass extinction of dinosaurs resulted from a protracted crisis, one that built over tens of thousands or hundreds of thousands of years before pushing earth over an ecological precipice. The fossil record of large animals in South Africa looks more consistent with extinction by a millennia-long volcanic eruption than by an asteroid or comet impact. Details of the research are presented. (5) Mostly mammals larger than approximately 44 kg (about 100 pounds). Some of the animals that went extinct are well known (like saber-toothed cats, mammoths, and mastodons). Others were less well known animals (like the short-faced skunk and the giant beaver). Some animals went extinct in North America but survived elsewhere (like horses and tapirs). Before this extinction the diversity of large mammals in North America was similar to that of modern Africa. As a result of the extinction, relatively few large mammals are now found in North America. See: Late Pleistocene Extinctions at Illinois State Museum (6) In the Jan. 2004 issue of "Nature" a team of international scientists says global warming would drive more than a third of the wildlife in the worlds most ecologically sensitive areas to extinction by 2050. They say that increasing temperatures will make it impossible for many plants and animals to fight for shrinking habitat in the Amazon, Australia, Africa and Mexico. In 1982, David Raup and John Sepkoski, both of the University of Chicago, examined marine invertebrate biodiversity in the Phanerozoic. They divided this 242-million-year sequence into 39 equal-length intervals, and defined an "extinction event" as an interval where at least 2% of all known marine invertebrate families became extinct. Raup and Sepkoski observed that such extinction events occur about every 26 million years.
According to Mikhail Medvedev and Adrian Melott, researches at University of Kansas, cosmic rays produced at the edge of our galaxy have devastated life on Earth every 62 million years. In addition to rotating around the galactic center, our sun moves toward and away from the Milky Way's center, and also up and down through the galactic plane. One complete up-and-down cycle takes 64 million years, suspiciously similar to Earth's biodiversity cycle. As the solar system rises above the central plane it sticks out like a cherry on top of the flying galactic pie, closer to the source of the cosmic radiation. See: Ancient Mass Extinctions, Cyclic and Caused by Cosmic Radiation? SoftPedia.
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In 1983, Marc Davis and Richard Muller, of the University of California at Berkeley, proposed that the Sun has a yet-undetected companion star with an eccentric orbit. The "unseen companion" is generally about 2 light years away from the Sun, according to Davis. As the companion star passes through the Oort cloud of comets surrounding the Sun, it launches many of these comets in the general direction of the earth