How Plate Tectonics Affected the Permian Extinction of Organic Life

Richard Kaczor

ES767

April 2008

 

 

Fossil Glossopteris leaf associated with coal deposits

and derived from glossopterid forests of the Permian age.

Found at Polarstar Peak in the Ellsworth Mountains in

Antarctica.1965. (from USGS website)

 

Introduction

 

The end-Permian mass extinction saw a loss of 90% of the species in the ocean and about 70% of vertebrate families on land (Erwin 1994).The event is dated at 251 million years ago.The precise timing and how long the extinction event lasted are still being debated.However, the end-Permian mass extinction was geologically a rapid event (~800,000 years).There is no conclusive evidence of a huge extraterrestrial impact similar to the one that caused the extinction of the dinosaurs.Currently the scientific community believes that it was a combination of events that caused the mass extinction and plate tectonics played an important role.

 

From USGS website.

Pangaea

 

Pangaea at the time of the Permian extinction extended from pole to pole.It was formed ~300,000 million years ago by the collision of Laurasia from the north and Gondwana from the south.It was surrounded by the superocean Panthalasa.Pangaea broke up about ~200 million years ago.At the time of the mass extinction, Pangaea produced glaciation, created change in regional and global climates and caused marine regression.

 

Marine Regression

During the marine regression Pangaea continental shelves were exposed to the atmosphere, negatively affecting the habitat of marine organisms.The sea level can decrease for different reasons.At the time of the Permian mass extinction Pangaea was at its maximum packing resulting in a lower sea level.This was caused when landmasses that formed Pangaea collided, compressing and thickening the supercontinentís crust.It resulted in a smaller landmass and a larger ocean basin for the Earthís fixed amount of water.Thermal uplift of Pangaea could have lowered the sea level in relation to the supercontinent.Heat could have accumulated underneath Pangaea, thermally uplifting the landmass in relation to the surrounding ocean.

 

Climates

The climate during the Permian mass extinction was affected by the size of Pangaea and the decrease of carbon dioxide in the atmosphere.Coastal area was lost when the continents reassembled to form Pangaea.A large percentage of mild moist coastal environments were replaced by a large arid interior climate.Pangaea spanned all latitudes, but did not have the range of climates that are found on Earth today.Pangaea blocked the flow of equatorial ocean currents, combined with the relatively high elevation along the western side caused the interior to be cool and dry (Rogers 2004, pg 173).Carbon dioxide in the atmosphere helps the Earth to retain heat.During periods of low sea level, large amount of silicate minerals are eroded from continental crust and carried to the oceans by rivers.These silicate minerals combine with carbon dioxide in seawater and produce solid precipitates.When carbon dioxide is drawn down into ocean sediments, there is less carbon dioxide in the atmosphere and the Earth cools forming glaciers near the poles.
 

Near view of glacial polish, striae and chatter marks,

developed by Permian ice on Proterozoic quartzite.

Ice moved toward upper right.Hallet Cove. Hammer for scale.

South Australia. n.d.(from USGS website)

 

Glaciation

During the time of the Permian extinction Pangaea stretched from pole to pole providing an opportunity for glaciers to form.The water trapped in the glacier ice lowers the sea level even more and also drives the heat engine of ocean vertical currents between the tropics and the poles.There is evidence that glaciers formed over the south pole and possible the north pole at the time of the Permian extinction.

 

Location of Siberian Traps

(Image from USGS website)

 

Siberian Traps

The Siberian Traps represents one of the largest flood basalt provinces on Earth and erupted 251 million years ago over a time interval of about 900,000 years.The eruptions spewed 2-3 million cubic kilometers of basalt lava, covering 3.9 million square kilometers to a depth of 400 to 3000 meters.It was so large and violent that it could have caused worldwide atmospheric contamination by injecting vast amounts of dust and sulphate gases into the atmosphere.The world climate could have been affected with the addition of volcanic gasses in the atmosphere (Benton 2003, pg 262).

 

Summary

 

Currently there is no single agreed upon event that caused the Permian mass extinction.It is believed that a combination of factors caused the worst mass extinction the world ever experienced.Environmental pressure on organisms caused by plate tectonics seems to have played an important role.The combination of a single supercontinent affecting climate, glaciation and sea level with the additional environmental stress of the Siberian Traps may have been the driving force that nearly wiped out life on Earth.

 

 

 

 References

 

Benton, J. B., When Life Nearly Died, The Greatest Mass Extinction of All Time. (Thames & Hudson Ltd, London, 2003).

 

Benton, M. J., Tverdokhlebov, V. P., Surkov, M. V. Nov. 4, 2004. Ecosystem remodeling among vertebrates at the Permian-Triassic boundry in Russia. Nature vol 432, p. 97-100.

 

Donovan, S. K., Mass Extinctions, Process and Evidence. (Columbia University Press, New York, 1989).

 

Erwin, D. H. Jan 20, 1994. The Permo-Triassic extinction. Nature vol. 367, p. 231-235.

 

Knoll, A. H., Bambach, R. K., Canfield, D. E., Grotzinger, J. P. Jul 1996. Comparative Earth History and Late Permian Mass Extinction. Science vol 273, p. 452-457.

 

Nance, R. D., Worsley T. R., Moody, J. B. 1988. The Supercontinent Cycle. Scientific America vol. 259/1, p. 72-79.

 

Renne, P. R., Basu A., Jul 12, 1991. Rapid Eruption of the Siberian Traps Flood Basalts at the Permo-Triassic Boundry. Science vol 253, p. 176-179.

 

Rogers, J.W., Santosh, M., Continents and Supercontinents. (Oxford University Press, New York, 2004).