The Cenozoic, Origin of Humans, and Present Mass Extinction.

Today's main points:

  1. Delta 13C curve in marine sediments at K-T boundary shows strong, but temporary negative shift that was thought originally to indicate that primary productivity collapsed - so called "Strangelove Ocean" of Wally Broecker and Ken Hsu.
  2. New evidence suggests that effect is due to increase in oceanic ecosystem efficiency due extinction of fecal pellet-producing plankton eaters.
  3. Recovery took millions of years.
  4. Early Paleocene terrestrial vertebrate faunas depauperate, increase in coals occurs.
  5. In Paleocene and Eocene some birds become large predators, mammals take over most fully terrestrial niches.
  6. Herbivorous mammals become larger and common in Eocene.
  7. Greatest warmth of Cenozoic in Late Paleocene and Early to middle Eocene.
  8. Dramatic transient negative excursions in delta 13C in Paleocene and Eocene may be due pulses of methane released from methane "ice" (clathrates) resulting in brief periods of extreme warmth.
  9. Grasslands start to become common in Oligocene and spread dramatically in Miocene, possibly increasing chemical weathering.
  10. Herbivores adapt to grasslands, grasses adapt to herbivores.
  11. Delta 13C goes progressively more negative in latter Cenozoic indicating increase in ecosystem efficiency and less organic carbon burial.
  12. CO2 is low in Cenozoic, Antarctic Ice cap by Miocene, Arctic by Pleistocene.
  13. Some think that increased chemical weathering and lower CO2 was brought about by rise of the Himalayas.
  14. Fluctuations in extent of glacial ice regulated by astronomical variations in the Earth's Orbit - so called "pacemaker of the Ice Ages" of Jim Hays.
  15. Primates diversify in Cenozoic, by Miocene there are members of the "Great Apes".
  16. Bipedal hominoids by about 4 Ma (early Pliocene).
  17. Modern Humans (Homo sapiens) by 100 to 200 Ky.
  18. Spread of Homo sapeins marked by widespread large mammal extinctions.
  19. Extinctions continuing largely as a result of population growth and associated habitat loss.

Updated March 22, 2005
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