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Mass Extinction Timeline

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by

David Kelley

on 29 April 2014

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Transcript of Mass Extinction Timeline

photo credit Nasa / Goddard Space Flight Center / Reto Stöckli
Mass Extinction Timeline
What are Mass Extinctions?
Time periods in the history of life on Earth during which exceptionally large numbers of species go extinct are called mass extinctions. These extinctions are quite different from the rate of extinction, which occurs even when the diversity of life is increasing. Many species vanished in five most catastrophtic mass extinctions and today, 99.9 percent of all species that have existed on Earth from then are now extinct.


How do we know?
The excavating of fossils (and the frequency of the same type of fossil found) and the methods of paleontology tell scientists when a Mass Extinction occurred, how, and what was majorly effected after the event that caused it.
Second Mass Extinction: The Late Devonian extinction
The Late Devonian extinction took place between 375 - 359 million years ago. While some extinction events occur fairly quicklly, the Denovian Extinction is composed of many smaller extinctions over the course of 20 million years. To this day its cause is unknown. However, evidence supporting the Devonian mass extinction suggesting that warm water marine species were the most severely affected in this extinction event, has lead many paleontologists to believe that an episode of global cooling, similar to the event which may have resulted in the Ordovician-Silurian mass extinction, may have lead to the Devonian extinction. Thus this theory suggests that the extinction of the Devonian was triggered by another glaciation event on Gondwana, which is evidenced by glacial deposits of this age in northern Brazil.

Third Mass Extinction: The Permian-Triassic extinction
The Permian-Triassic extinction happened about 251 million years ago and was Earths worst mass extinction. 95 percent of all species, 53 percent of marine families, 84 percent of marine genera, and an estimated 70 percent of land species such as plants, insects and vertebrate animals were killed during this catastrophe. Direct evidence for this period has not been found but many scientists believe a comet or asteroid impact led to this extinction. Others think that volcanic eruption, coating large stretches of land with lava from the Siberian Traps, which are centered around the Siberian City of Tura, and related loss of oxygen in the seas were the cause of this mass extinction. Still other scientists suspect that these events are connected, and that the impact of the comet or asteroid triggered the volcanism.

Fourth Mass Extinction: The end Triassic extinction
The End Triassic extinction, taking place roughly 199 million to 214 million years ago, was most likely caused by massive floods of lava erupting from the central Atlantic magmatic province triggering the breakup of Pangaea and the opening of the Atlantic Ocean. The volcanism may have led to deadly global warming. Rocks from the eruptions now are found in the eastern United States, eastern Brazil, North Africa and Spain. 22 percent of marine families, 52 percent of marine genera, and an unknown percentage of vertebrate deaths were the result.

The Ordovician-Silurian extinction occurred about 439 million years ago due to a drop in sea levels as glaciers formed followed by rising sea levels as glaciers melted. During this extinction 25 percent of marine families and 60 percent of marine genera were lost. A temporary ice age was created at this point in time.

First Mass Extinction: The Ordovician-Silurian extinction
The second possible ice age
Volcanic reaction by asteroid impact
Earth quakes followed by lava flows
Finally, the Cretaceous-Tertiary extinction occurred about 65 million years ago and is thought to have been aggravated, if not caused, by the impact of a several-mile-wide asteroid that created the Chicxulub crater now hidden on the Yucatan Peninsula and beneath the Gulf of Mexico. Yet, some scientists believe that this mass extinction was caused by gradual climate change or flood-like volcanic eruptions of basalt lava from the Deccan Traps in west-central India. During this extinction, 16 percent of marine families, 47 percent of marine genera, and 18 percent of land vertebrate families including the dinosaurs.


Fifth Mass Extinction: Cretaceous-Tertiary
As unbelievable as it may sound, after having read through the five mass extinctions, the sixth mass extinction is in progress, now, with animals going extinct 100 to 1,000 times (possibly even 1,000 to 10,000 times) faster than at the normal background extinction rate, which is about 10 to 25 species per year. Many researchers claim that we are in the middle of a mass extinction event faster than the Cretaceous-Tertiary extinction which wiped out the dinosaurs, due to over population of humans, mass producing, habitat destruction and clear-cutting of forests and the mortality to death ratio.

Sixth?
Graph
References
http://www.endangeredspeciesinternational.org/overview.html
woodstown.org/cms/lib4/NJ01001783/Centricity/Domain/8/.../act5.pdf‎

news.nationalgeographic.com/.../130321-triassic-mass-extinction-volcan...‎

Originally Created by Ashley Mattingly, Modified by Mr. Kelley
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