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TITLE: Clues to a Very Different Earth


Cratons contain some unusual rocks and valuable ore deposits that bear the imprint of conditions that once prevailed on Earth.

  • Until about two billion years ago, Earth’s atmosphere contained one percent or less of its present oxygen levels.
  • Two-and-one-half billion years ago, Earth produced five times as much heat as today.


Valuable Ore

These layers are part of South Africa’s 2.1- billion-year-old Bushveld Complex. One 5.5-m (18-ft) thick layer in this Complex contains more than half of Earth’s known platinum reserves.

  [Photo: Layers of Ore]

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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits