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Life Before Oxygen
About three billion years ago, single-celled underwater bacteria similar to modern cyanobacteria consumed carbon dioxide as they photosynthesized, releasing oxygen in the process. In this way, an atmosphere full of volcanic carbon dioxide gradually changed into an oxygen-rich atmosphere in which animal life could survive, except for some primitive organisms, who retreated to oxygen-poor environments. This video segment shows researchers as they search for these organisms, which are now considered tiny time capsules from the time before there was oxygen on Earth. The segment is one minute thirty-nine seconds in length. A background essay and list of discussion questions are also provided.
Intended for grade levels:
  • Intermediate (3-5)
  • Middle (6-8)
  • High (9-12)
Type of resource:
  • Visual:
    • Video
  • Text:
    • Ref. material
  • Biology
  • Geological Sciences:
    • Geologic time
    • Paleontology
Technical requirements:
QuickTime plug-in
Cost / Copyright:
No cost
Source: Interactive NOVA "Earth". Copyright 2002-2006, WGBH Educational Foundation. All rights reserved.
DLESE Catalog ID: DLESE-000-000-009-851
Educational standards:
  • National Science Education Standards (NSES):
    • K-4:
      • C - Life science:
        • Characteristics of organisms
        • Organisms and environments
      • D - Earth and space science:
        • Changes in earth and sky
      • F - Science in personal / social perspectives:
        • Changes in environments
    • 5-8:
      • B - Physical science:
        • Transfer of energy
      • C - Life science:
        • Diversity and adaptations of organisms
        • Population and ecosystems
        • Structure and function in living systems
      • D - Earth and space science:
        • Earth's history
        • Structure of the earth system
    • 9-12:
      • B - Physical science:
        • Chemical reactions
      • C - Life science:
        • Biological evolution
        • Interdependence of organisms
        • The cell
      • D - Earth and space science:
        • Geochemical cycles
        • Origin and evolution of the earth system
Resource contact / Creator / Publisher:
Publisher: WGBH Educational Foundation