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Effects of Past Global Change on Life (1995) / Chapter Skim
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Pages 29-29

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From page 29...
... If tiny ur-metazoans developed circulatory systems, then a PO2 increase to more than 6 to 10~o PAL would remove this environmental barrier against the evolution of macroscopic animals. On the other hand, if macroscopic size preceded the efficient internal circulation of fluids, PO2 increases to nearly modern levels would be necessary for large animal metabolism.
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Key Terms

  • macroscopic animals
  • late proterozoic
  • earth history


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