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Effects of Past Global Change on Life (1995) / Chapter Skim
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Pages 25-27

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From page 25...
... At about 1800 Ma the fossil record improves markedly (e.g., Schopf, 1983) , so it is not clear that paleontological first appearances necessarily record evolutionary innovations.
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From page 26...
... At about 1% PAL, aerobic metabolism by single-celled organisms becomes possible, while an effective ozone screen expands the ecological possibilities of life. When PO2 rose to 1 to 2% PAL, aerobic metabolism probably followed quickly in organisms already protected against oxygen toxicity.
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From page 27...
... OXYGEN AND PROTEROZOIC EVOLUTION: AN UPDATE ~ ~ ~ \-e ~ ~ ~ ~ a %5\ ~ ~ ~ ~ ~ \\\N \\\\N ~ 1/ 1/ as/ ~ Purple Bacteria / ~ Microsporidians have prokaryote-like features of ribosomal organization and lack mitochondria; unlike Giardia they have a well-developed endomembrane system. Trichomonads also lack mitochondria, and free-living species live as aerotolerant anaerobic heterotrophs (Margulis et al., 19891.
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Key Terms

  • aerobic metabolism
  • fossil record


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