What Have We Got To Lose?: A Brief History of Mass Extinction Events

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http://www.scienceofwonder.org/what-have-we-got-to-lose-a-brief-history-of-mass-extinction-events/

Currently, some scientists warn that we are on the brink of a sixth mass extinction due to a mixture of climate change, overhunting, habitat destruction, and pollution. If all the species that are listed at variable levels of endangerment were to go extinct, our planet could see another extinction event in a matter of mere centuries. Even if we are faced with another mass extinction, what is really at stake?

 

Mass extinctions occur when there is a sharp decrease in biodiversity. While there are constantly new species dying out and emerging, there have been five times in history that significantly reshaped the levels of life on Earth:

 

The Ordovician-Silurian event occurred ~445 million years ago, with a loss of 57% of all genera. It is thought that the movement of continental land to the South Pole caused much of the coastal water to freeze. This decreased sea levels, wiping out the extensive amount of life in shallow waters.

 

The Late Devonian extinction event occurred ~370 million years ago, and a combination of factors is thought to be responsible for 50% of all genera dying out. At this time, land vegetation increased. Through photosynthesis, much of the carbon dioxide was taken out of the atmosphere, cooling the earth. Glaciers formed, decreasing sea levels, which was problematic for great numbers of marine life.

 

The Permian-Triassic event was the biggest in history, with 83% of all genera dying ~250 million years ago. Land vertebrates saw a loss of 70% of all species, while marine life dropped 96%. A combination of factors was responsible, including immense volcanic eruptions that increased the temperature of the earth, the formation of Pangaea which resulted in fluctuating ocean currents, earthquakes, and drastic temperature changes for land life. 

 

The Triassic-Jurassic extinction occurred ~200 million years ago, and resulted in the loss of 48% of all genera. The details behind this event are not entirely understood, but many scientists believe that extensive eruptions not only emitted over 2 quadrillion kilometers of lava, but sulfur and carbon dioxide as well, creating an environment inhospitable for life.

 

Cretaceous-Paleogene is the most well known, occurring 65.5 million years ago, wiping out 50% of all genera, including most dinosaur species. While it is most commonly believed that an asteroid caused the event, others believe the effects of the collision combined with movement of the continents and volcanic eruptions to end the Age of Reptiles, and usher in the Age of Mammals.

 

So, what is at stake if we’re on the verge or even in the midst of a sixth mass extinction? A hell of a lot, actually. Some say that any attempts to conserve animals or decrease pollution would only delay the inevitable. However, a greater number of scientists believe we are not yet to the point of no return and still have time to make significant changes and maintain diversity of life on Earth.

Source: Array

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