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Science — Third Preparatory

Science — Third Preparatory

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Unit 4 — Dating Planet Earth

Science — Third Preparatory

Unit 4 — Dating Planet Earth

2.9 Summary of Lesson 2

2.9 Summary of Lesson 2

Comparison aspectMain ideaExampleKeywords
Geologic time scale
  • eons
  • eras
  • periods
  • epochs (largest to smallest)
—eonserasperiodsepochs
•Rock and fossil records reveal eventsmountain building and volcanic activityRockfossilrecordsreveal
Relative age
  • law of superposition
  • index fossils
—superpositionindexfossils
Absolute age
  • radioactive isotopes and half-life
  • fraction left = (1/2)ⁿ
—radioactiveisotopeshalflife
•Earth is about 4.6 billion years old—Earthbillionyears
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