The terminal Cretaceous extinction

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The terminal Cretaceous extinction
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The terminal Cretaceous extinction

• A quite sudden extinction on a geologic time
  scale
• The dinosaurs plus many other groups of animals
  and plants died gymnosperms and angiosperms
  suffered heavy losses
• This was as much a land extinction as marine
  extinctions

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The terminal Cretaceous extinction

• In the marine environment
• The ammonoids disappeared
• The pleisosaurs and giant turtles disappeared
• About 90 of all planktonic nannoplanktons and
  forams died out
• Many groups of mollusks disappeared
• The rudists were wiped out

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The terminal Cretaceous extinction

• Discoveries during the past few years have
  established beyond a reasonable doubt that an
  asteroid (10 km wide) impacted with Earth
• Luis Alvarez and son Walter discovered iridium in
  a thin layer in Italy, at the Cretaceous
  Tertiary boundary
• This layer also found in many other places in the
  world

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Iridium layer
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• Why was iridium not expected?
• Iridium is very rare on Earth but common in
  meteorites (an element of the platinum group)
• Shocked quartz
• Tektites (spherical grains of glass)
• Microscopic diamonds
• Soot residue from plants that burned

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Shocked quartz
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Tektites
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Iridium-rich sedimentary layers
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The terminal Cretaceous extinction

• So, where is the crater?
• Chicxulub Crater is 200 m in diameter, just north
  off the Yucatan Peninsula in Mexico
• This crater is one of the largest impact
  structure in the last 4 Ga
• The asteroid struck at a low angle, 20o to 30o
  from the Earths surface

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The terminal Cretaceous extinction

• A fiery vapor cloud would have moved northwest
  over N. America
• 75 of all flora in these areas died out (this is
  not seen in Australia and New Zealand)
• The microspherules (tektites) are in a 1-m layer
  in Mexico, 10 cm in Texas, and 5 cm in New Jersey

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The terminal Cretaceous extinction

• What would this extinction have looked like had
  you been there?
• 1) Perpetual night dust would have lasted for
  several months plants could not conduct
  photosynthesis
• 2) Cold winter weather for months
• 3) After the cold abnormal heat greenhouse
  effect from aerosols trapped in the air

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The terminal Cretaceous extinction

• 4) Acid rain the asteroid penetrated limestones
  and sulfate evaporites sulfur dioxide formed and
  reacted with water
• 5) Fires many wild fires, especially in North
  America
• Fishes, crocodiles, turtles, and amphibians were
  the best survivors. Why?

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The terminal Cretaceous extinction

• Could there have been other causes?
• Volcanic activity - carbon dioxide, however,
  spiked for only a very short time Deccan traps
  formed
• Magnetic reversals prevented shielding from
  cosmic rays?
• Supenova blast?
• Environmental factors?