Greatest Mass Extinctionsof the

Phanerozoic Eon

Group 4Jennifer Sullivan

Zoe GentesAJ Infante

Amy LombariDennis Titterton

The Basics

end-Permian Extinction ~251 Ma (#1 greatest mass extinction)

~94% of all marine life; up to ~70% of land species.

Late Ordovician Extinction ~443 Ma (#2 greatest mass extinction)

~65% of all life;

General Causes

Primary Suspects

Volcanism – Gas emissions of Hydrogen Sulfide can lead to anoxia in deep ocean environments, which then may reach the atmosphere. H2S in the atmosphere also weakens the ozone layer, allowing harmful levels of UV radiation to reach the Earth.

H2S Emissions – Global warming can cause an imbalance between organisms and bacteria that reduce Sulfate, allowing an increase in Hydrogen Sulfate in the oceans. This can rise into the atmosphere as well, lethal to life everywhere.

Methane Hydrate Gas – Methane gases can be released by volcanism.

Anoxia – Oceans became severely anoxic by the end of the Permian.

General Causes

Secondary Suspects

Sea Level Fluctuations – A marine regression occurred in Late Permian, killing shallow marine habitats. There is only partial evidence for regressions being linked to extinctions.

Formation of a Supercontinent – This reduced the amount of shallow marine environments and altered oceanic circulations, as well as the changes in weather and climates to seasonal monsoons along the coasts and arid climates within the continent's interior.

Impacts – Although impacts have led to other large extinctions, no evidence for a part in the Permian-Triassic extinction has been found.

Gamma Ray Bursts – When a star explodes it sends out gamma ray bursts. It is suspected that this initiated the Ordovician extinction when a gamma ray burst occurred close enough to the Earth for it to receive UV radiation.

End-Permian: The Likely Causes

Scientists generally conclude that the P/T extinction was due to a combination of events that fell together much like a “domino effect” causing phases or “pulses” of extinctions that spanned over ~8 million years.

During the Permian, ocean salinity dropped significantly for the first time.

Oxygen levels in the atmosphere went from high (~30%) to very low (~15%).

There is evidence for global warming as well as cooling and glaciation.

Extreme erosion on Pangaea created extensive bare, arid environments.

Large-scale ocean regression led to oxidization of trapped organic matter in the now-exposed shallow marine environments.

A gigantic volcanic event spread flood basalts, now called the Siberian Traps.

Lastly, a large-scale transgression flooded habitats along the shore.

End-Permian: The Evidence

Siberian Traps: Extensive volcanic activity (basaltic lava flows) occurred towards the end of the Permian, but before the “pulses” of extinction began. The remains are located in Russia and span 2,000,000 square kilometers.

Studies on the Maokov Formation, located in Meishan, China.

333 marine fossil species were traced in the rock layers.

Isotopic analysis of volcanic ash layers were used to find relative ages.

Concluded that the range of extinctions occurred within 500,000 years.

http://palaeo.gly.bris.ac.uk/Palaeofiles/Permian/Map.html

Siberian Traps

End-Permian: The Evidence

The excessive lava floods produced CO2 and SO2 emissions.

Which led to global warming (followed later by short-term cooling), acid rain, sea level fluctuations, and the release of methane reservoirs.

Global warming reduces an ocean's ability to retain oxygen, thus making the deep ocean anoxic.

Gas levels increased, leading to extreme anoxia around the globe that spread through the atmosphere as well as the ocean.

Such large amounts of CO2 can severely damage the ozone layer, enough to allow lethal UV radiation to penetrate.

Late Ordovician Mass Extinction

Significant volcanic activity and weathering of silicate terrains from the mountains increased CO2 levels.

The increased CO2 levels raised temperature, however as Gondwana moved towards the South Pole, glaciation covered the land.

When the ice sheets formed they reduced the silicate weathering lowered the sea level.

However CO2 levels continued to rise and led to a Greenhouse effect that ended the period of glaciation.

Fluctuations in sea level occurred during these stages as ice sheets formed and melted.

Affected Life

Permian/TriassicExtinction

(Only known extinction event for insects), trilobites, blastoids, euryptids, fusilinids, rugose and tabulate corals, some bryozoan and brachiopod orders, acanthodians, placoderms, cordaites, glossopteris, pelycosaurs, & more.

Late OrdovicianExtinction

Brachiopods, bryozoans, graptolites, tabulate and rugose corals, stromatoporoids, conodonts, & more.

(Benton and Twitchett, 2003)

Reconstruction of ancient seabed in southern China representing before and after the P/T mass extinction.

Permian-Triassic Extinction Example

End-Permian vs. Late OrdovicianSimilarities Global warming and global cooling events, including glaciations. Marine regressions. Marine life was affected the most for both of these mass extinction events. Increased CO2 levels. Anoxia

Differences

End-Permian Late Ordovician

Formation of a supercontinent. Gondwana positioned by South Pole.

Ocean salinity level dropped significantly. Large mountain building events.

Large amount of volcanism. Gamma Ray Burst.

Conclusion

Glaciation is considered the most significant cause for extinctions in the Late Ordovician mass extinction.

The basaltic floods had a significant and direct influence on the Permian-Triassic mass extinction.

The type of extinction even that occurred forming the Permian/Triassic boundary would be the most likely to occur again today.

We are moving towards a period of global warming due to an increase in CO2 emissions. Our ozone layer is also beginning to weaken.

References Benton, Michael J.; Twitchett, Richard J., 2003, How to kill (almost) all life: the end-Permian extinction event, University of

Bristol, UK, TRENDS in Ecology and Evolution, Vol.18, No.7., pp.358-365.

Erwin, Douglas H., 2006, Extinction: how life on earth nearly ended 250 million years ago, Princeton University Press, Princeton, New Jersey, pp.10-15

Finney, Stanley C.; Berry, William B. N.; Cooper, John D.; Ripperdan, Robert L.; Sweet, Walter C.; Jacobson, Stephen R.; Soufiane, Azzedine; Achab, Aicha; Noble, Paula J., 1999, Late Ordovician mass extinction: A new perspective from stratigraphic sections in central Nevada, Geology, Geological Society of America, Vol.27, No. 3, p.215-218.

Goodwin, Anna; Wyles, Jon; Morley, Alex, 2001, The Permo-Triassic Extinction, University of Bristol, UK, <http://palaeo.gly.bris.ac.uk/Palaeofiles/Permian/intro.html>

Hallam, A.; Wignall, P.B., 1997, Mass Extinctions and Their Aftermath, Oxford University Press, N.Y., p.4.

Sheehan, Peter M., 2001, The Late Ordovician Mass Extinction, Annual Reviews: Earth Planetary Science, 29:331-64.

Warmuth, Laura, 2008, The Late Ordovician Mass Extinction: A review of the Second-Largest Extinction Event in Earth's History, <http://evolution.suite101.com/article.cfm/the_late_ordovician_mass_extinction>

Thomas, Ellen, 2001, Biodiversity - Invasive Species - Mass Extinctions, <http://ethomas.web.wesleyan.edu/ees123/mass_extinctions.htm>