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Science — Third Preparatory

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Unit 4 — Dating Planet Earth

Science — Third Preparatory

Unit 4 — Dating Planet Earth

2.3 Reading Earth’s history from rocks and fossils

2.3 Reading Earth’s history from rocks and fossils

  • Studying geologic structures, the sequence of rock layers and the fossils helps us infer events that happened in the past.
  • Examples:
Comparison aspectMain ideaExampleKeywords
The Red Sea mountains and Uweinat mountains
  • are made of igneous (granite) and metamorphic rocks. Igneous rocks like granite form deep within Earth by the cooling of magma
  • metamorphic rocks form from other rocks under great heat and pressure. So these mountains are among the oldest parts of Earth’s crust
  • formed deep inside the Earth
—madeigneousgranitemetamorphic
Basalt covering limestone at Abu Rawash.
  • Basalt is an igneous (volcanic) rock
  • limestone is a sedimentary rock that forms on the floor of a sea. So the area was first under the sea (limestone formed)
  • the sea retreated
  • and later volcanic eruptions covered the limestone with basalt
—igneousvolcanicrocksedimentary
Marine fossils on the peaks of the Himalayas.
  • Marine fossils form only in the seas. Their presence on mountain peaks shows the area was an ancient sea floor
  • which was uplifted when tectonic plates collided to form the mountain range
—formseaspresencemountain
•A fossil type found in one layer worldwide and then absent from higher layers
  • the dinosaurs
  • indicates the extinction of those organisms (a sudden global mass extinction
  • probably due to a meteorite impact or severe climate change)
fossiltypefoundlayer
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