Mass Extinctions

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Mass Extinctions

• Michael Sharpe
• Evolution
• Bellarmine University

2
Background

• Mass extinction the act of extinguishing
  something done in a relatively large scale
• 5 Major and 1 Current
• Many possible causes have been hypothesized, but
  none are definitely confirmed.
• After each extinction, millions of years were
  necessary for the biodiversity of species to be
  re-established.
• The most effective agent in the extinction of
  species is the pressure of other species (Alfred
  R. Wallace).

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Size and Time of Extinctions
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Cambrian Period

• 543-510 million years ago
• World mostly under water organisms were aquatic
• Small skeleton-like sponges and mollusks present
• Most important species echinoderms, mollusks,
  brachiopods, archaeocyathids, and trilobites

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Species Affected
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2 Hypotheses Merge Together?

• Glaciation Hypothesis decrease in global
  climatic conditions caused by continental
  glaciers at the Cambrian-Ordovician boundary (big
  word for Ice Age)
• Killed off all warm water creatures
• Oxygen Cooling and Depletion Hypothesis
• Decreased sea levels
• Reduced environment for marine species

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Ordovician Period

• 510- 438 million years ago
• Still restricted by water
• Species from Cambrian were present
• New species from diversification appeared
• Displayed higher ecological complexity
• Species present were cephalopods, corals,
  bryozoans, crinoids, graptolites, gastropods, and
  bivalves

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Species Around
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Ordovician Extinction

• 2nd most devastating to marine community
• Caused the disappearance of one third of all
  brachiopod and bryozoan families, as well as
  numerous groups of conodonts, trilobites, and
  graptolites
• More than one hundred families of marine
  invertebrates perished
• Proposed mechanism glaciation of the continent
  Gondwana (lower half of Pangaea)

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Gondwana
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Devonian Period

• 408-360 million years ago
• Re-diversification occurring
• First appearance of sharks and bony fish
• Oceans dominated by reef builders
• First signs of amphibians, insects, and the first
  true land plants
• Extinction primarily affect reef builders

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Species Present
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Permian Period

• 286-248 million years ago
• Formation of the super-continent Pangaea
• Extensive development and diversification of
  terrestrial vertebrate
• Reduction of marine communities
• Corals and trilobites were present, but rare
• Extinction in this period was largest ever
• 90-95 of marine species were eliminated

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Victims of Permian Extinction
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Theories of Permian Extinction

• Glaciation of Gondwana
• Reduction of continental shelves by the formation
  of Pangaea
• Severe climatic fluctuations from glaciation
• Lava eruptions in Siberia

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End-Cretaceous Period

• 144-65 million years ago
• Abundant life, but little diversity
• Triassic, Jurassic, and Cretaceous periods
  brought about many new species
• First appearances by dinosaurs, mammals,
  pterosaurs, frogs, and turtles.
• 85 of species died in End-Cretaceous
  extinction, making it the 2nd largest

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Victims of End-Cretaceous Ext.
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Causes of End-Cretaceous Ext.

• The more prominent hypotheses invoke
  extra-terrestrial forces
• Meteorite impacts
• Comet showers
• Older hypotheses cite earthly mechanisms
• Volcanism
• Glaciation

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Extinction Yet to Come?

• Holocene Epoch current era we are in right now
• Extinction caused by industry and deforestation
• Killing 100-1000 species for every 200 square km
  tropical forest and 100,000 square km of
  rangeland
• So, when is our time up?

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References

• http//www.lassp.cornell.edu/newmme/science/extinc
  tion.html
• http//www.well.com/user/davidu/extinction.html
• http//www.tulane.edu/sanelson/geol204/impacts.ht
  m
• http//www.newscientist.com/news/news.jsp?idns999
  94797
• http//www.nature.com/nsu/020603/020603-6.html
• http//hannover.park.org/Canada/Museum/extinction/
  extincmenu.html
• http//www.nhm.ac.uk/science/intro/palaeo/project3
  /
• http//www1.tpgi.com.au/users/tps-seti/crater.html
  
• cas.bellarmine.edu/tietjen