BAESI: The Fossil Record

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BAESI The Fossil Record

• Environment and the History of Life
• Jonathan Hendricks
• SJSU Department of Geology
• jhendricks_at_sjsugeology.org

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Uniformitarianism

• Uniformitarianism the idea that the physical and
  chemical laws of nature have remained the same
  throughout Earths long history.
• Uniformitarianism is the central principle of
  geology.
• This idea allows us to interpret Earths past
  history and predict its future, if we understand
  how the Earth operates today.
• The present is the key to the past.

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Interpreting Ancient Environments

• 1) Study the types of rocks that are preserved.
• Are any similar rocks being formed today?
• If so, what type of environment are they being
  formed in?
• Example if you want to know how volcanic rocks
  formed in the past, study how they form today.
• 2) Use fossils!

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Taxonomic Uniformitarianism

• Taxonomic Uniformitarianism the idea that an
  extinct fossil organism lived in a similar way
  and in a similar range of environmental
  conditions as its closest living relative.

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Taxonomic UniformitarianismContinued

• However, it is not always possible to apply this
  principle, especially when either
• A fossil organism has NO closely related (or
  identifiable) living relatives.
• Or, significant evolution has occurred (e.g., a
  lineage has increased or decreased its
  environmental tolerances).

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Example

• Suppose you are interested in determining whether
  a layer of sedimentary rock was deposited in
  freshwater or saltwater.
• A fossil starfish found in the rock layer could
  resolve this problem.
• All modern starfishes live exclusively in
  saltwater.
• Thus, one assumes that the sedimentary rock layer
  was deposited in salt water.

• Slide shows a photograph of a modern starfish.

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• Mass Extinctions

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Thomas Jeffersons Search for the Mastodon

• It may be asked why I list the mammoth
  referring to the mastodon as if it still
  existed? I ask in return, why should I omit it,
  as if it did not exist? Such is the economy of
  nature, that no instance can be produced of her
  having permitted any one race of her animals to
  become extinct of her having formed any link in
  her great work so weak as to be broken.
• - Thomas Jefferson, 1781

• Slide shows an antique illustration of the Great
  Chain of Being.

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What are Mass Extinctions?

• Many species go extinct (gt 30 number must
  exceed normal background rates of extinction).
• Species of varied taxonomic groups and ecologies
  affected.
• Global event that occurred over a short period of
  time.

• Slide shows a graph of Phanerozoic diversity
  patterns.

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The Big 5 (or 6) Mass Extinctions

• End-Permian (80)
• End-Cretaceous (50)
• End- Ordovician (57)
• Late Devonian (50)
• End-Triassic (48)
• Today.
• Note values are extinctions of marine genera.

Eon Era Period Epoch
Phanerozoic Cenozoic Neogene Pleistocene
Phanerozoic Cenozoic Neogene Pliocene
Phanerozoic Cenozoic Neogene Miocene
Phanerozoic Cenozoic Paleogene Oligocene
Phanerozoic Cenozoic Paleogene Eocene
Phanerozoic Cenozoic Paleogene Paleocene
Phanerozoic Mesozoic Cretaceous -
Phanerozoic Mesozoic Jurassic -
Phanerozoic Mesozoic Triassic -
Phanerozoic Paleozoic Permian -
Phanerozoic Paleozoic Pennsylvanian  
Phanerozoic Paleozoic Mississippian -
Phanerozoic Paleozoic Devonian -
Phanerozoic Paleozoic Silurian -
Phanerozoic Paleozoic Ordovician -
Phanerozoic Paleozoic Cambrian -
Proterozoic - - -
Archean - - -
Today (Recent)

• Slide shows the geological time scale.

65 Ma
251 Ma
542 Ma
2.5 Ga
4.6 Ga
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What happened at the end of the Permian??
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Earth at the End of the Permian
Pangea

• Slide shows a map reconstruction of Pangea.

Source http//jan.ucc.nau.edu/rcb7/mollglobe.htm
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The End-Permian Mass Extinction

• 90 marine species (80 genera, 50 families) go
  extinct.
• Trilobites, tabulate and rugose corals, many
  types of brachiopods, many echinoderms, etc.
• 75 families of land vertebrates.
• Many plants.

• Slide shows a photograph of a fossil tabulate
  coral.

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The End Permian Mass Extinction

• Todays oceans still reflect the winners and
  losers of events at the end of the Permian
  (Erwin, 2006).

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What Caused It?

• Short answer scientists are not sure.
• Any hypothesis must explain extinction patterns
  in the sea and on land.
• Many scientists have looked for evidence of an
  asteroid or comet impact at the Permian-Triassic
  boundary, but have not produced conclusive
  results.
• Siberian flood basalts (called the Siberian
  Traps) may be a likely culprit.

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Siberian Flood Basalts

• Erupted in region that is now Siberia from about
  252 to 251 Ma almost coincident with P/T
  boundary (251 Ma).
• Mass of erupted magma equal to extent of
  continental U.S. 4 million cubic kilometers.

Pangea

• Slide shows a map reconstruction of Pangea,
  detailing the position of the Siberian Traps and
  their extent.

Source http//jan.ucc.nau.edu/rcb7/mollglobe.htm
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Siberian Flood Basalts

• Possible consequences
• Dust clouds.
• Acid rain.
• Massive volcanic release of CO2.
• Global warming ( 6º C). As temp. increases, O2
  becomes less soluble in water, resulting in
  anoxic (oxygen-free) conditions in shallow water
  - may have driven marine extinction.
• Warming may have also caused melting of frozen
  gas hydrates in the oceans, releasing substantial
  amounts of methane, another greenhouse gas.
• Runaway greenhouse effect?