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Understanding the Role of Extinctions in Shaping Biodiversity, Slides of Theory of Evolution

The concept of mass extinctions, the role of background extinctions in shaping biodiversity, and the ecological significance of major extinction events throughout the phanerozoic era. The background rate of extinctions, the ecological significance of mass extinctions, and the causes of some of the most catastrophic events in earth's history, including the cambrian, ordovician, devonian, and permian extinctions.

Typology: Slides

2012/2013

Uploaded on 01/02/2013

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Lecture 23: Mass Extinctions
•Biodiversity: balance b/w spec’n & extinction
•> 99% of all species are extinct
•Because of:
1) Background extinctions:
•gen’lly due to biotic factors
•e.g. competition, predation etc.
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Download Understanding the Role of Extinctions in Shaping Biodiversity and more Slides Theory of Evolution in PDF only on Docsity!

Lecture 23: Mass Extinctions

  • Biodiversity: balance b/w spec’n & extinction

  • 99% of all species are extinct

  • Because of:
  1. Background extinctions:
  • gen’lly due to biotic factors
  • e.g. competition, predation etc.

Background Rate

  • marine families: → relatively constant
  • ~ 5 - 10 families / my

mass extinctions

e.g. Sepkoski & Raup (1982)

Mass Extinctions of the Phanerozoic:

“The Big 5”

1.) Cambrian (540 - 510 mya):

  • Explosion of diversification
  • Marine; soft-bodied (few fossils)
  • Evidence for ~ 4 separate events
  • Trilobites, conodonts, brachiopods hit hard Cause: Glaciation:
    • sea level ↓ (locked in ice)
    • cold H 2 O upwelling & spread
    • ↓ O 2 levels?

2.) Ordovician (510 - 438 mya)

  • 2 nd^ most devastating to marine organisms
  • Echinoderms, nautiloids, trilobites, reef - building corals Causes: Glaciation of Gondwanaland
  • evidence in Saharan deposits
  • drifted over N. pole (cooling)
  • sea level ↓
  • losses correspond to start & retreat of glaciers

4.) Permian (286 - 245 mya)

  • formation of Pangea: continental area > oceanic
  • Devastation (~245 mya): ~96% marine spp; 75% terrestrial spp Causes: a) formation of Pangea? b) vulcanism? - basaltic flows in Siberia
    • sulphates in atmosphere → ash clouds c) glaciation at both poles: major climatic flux d) ↓ salinity of oceans?