Permian and Cretaceous Mass Extinctions

Topics: Extinction event, Dinosaur, Cretaceous–Tertiary extinction event Pages: 5 (1433 words) Published: July 26, 2011
Assess the different hypotheses put forward for the mass extinctions at the end of the Permian and Cretaceous (KT) Periods.

A mass extinction is an event in which at least 25-75% of species in the global environment are eradicated in a short period of time. Where as a regional extinction event is when the extinction is confined to a specific zone. Five mass extinctions have occurred throughout time, two of the most well known of these are the Permian and Cretaceous extinction events.

There are several hypotheses that are used to explain the causes of mass extinctions. Climate change, the warming or cooling of global environments over a short period of time, can lead to other occurrences. Shifts in climate can cause extinction by moving or eliminating entire habitats. Global cooling most impacts the tropical areas as in the polar and deep-water flora and fauna have already adapted to cool environments. The major effect of global warning is on the circulation of ocean currents and the reduction of dissolved oxygen in water bodies. Anoxia, no or little dissolved oxygen in the sea, is the major cause of marine extinction. Anoxia is linked to global warming and sea levels rising.

Bolide, impact by asteroids or meteorites, can cause several environmental causatums. The dust from the impact can block out sunlight for years, creating permanent a winter, leading to the collapse of ecosystems. With no sunlight, plants cannot photosynthesis, so they will eventually die. Decaying plant and animal life leads to release of noxious gases, lessening the O2 levels in both atmosphere and lithosphere. The bolide impact can cause huge earthquakes and tsunamis. Molten debris raining down after the impact can start wildfires across the globe, further adding to the noxious atmosphere. The release of carbon dioxide and sulfur dioxide from mega-volcanoes can impact global temperatures, leading to global warming, sea level rises and acid rain. Volcanic eruptions have are commonly located around the times of mass extinctions, and can add to the already stressed environment.

The Permian extinction event occurred around 248 million years ago and marks the end of the Paleozoic Era. It is the largest extinction event in history, with approximalty 96% of all life becoming extinct. There are several hypotheses about what caused the Permian extinction, but as much of the evidence about what occurred has been lost over time, it is hard to tell exactly what caused this mass extinction.

At the time of the Permian extinction, the earth was joined as the large super-continent Pangea. One theory to account for this extinction is that the earth experienced an ice age for approx 40 000 years, which was followed by an extreme global greenhouse effect. The regression and transgression of fluctuating climate caused rainfall patterns to change. Very few life forms would have been able to withstand the extreme climatic changes. There is evidence supporting this theory in Greenland and Russian rock strata.

The fluctuating climate caused a fluctuation of sea levels, with first a fall in levels then with a rise. This rise, so soon after a fall in sea levels would have placed extreme stress on the marine community that was trying to adjust to the already change marine environment. The regression in sea levels exposed organic matter that was decomposed to form large amounts of CO2 causing a drop in oxygen levels and an anoxic marine environment. The large carbon dioxide levels could have contributed to more global warming.

Nearing the end of the Permian period there were mass eruptions in the Siberian traps approx 2 million km2. This volcano released massive amounts of carbon dioxide and sulfur dioxide, leading to acid rain and blackout of sunlight. It is thought that this caused the global cooling, and once the eruptions ended, intense global warming cause by the noxious gases released during the eruptions, which lead to the fluctuating sea levels....

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