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Warm-up

Warm-up. How old do you think the Earth is? What do you think fossils are?. Geologic Time. The Beginning of Earth. Earth formed about 4.6 billion years ago. Gravity pulled the densest elements to the center of the planet. After about 500 million years, a solid crust formed on the surface.

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Warm-up

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  1. Warm-up • How old do you think the Earth is? • What do you think fossils are?

  2. Geologic Time

  3. The Beginning of Earth • Earth formed about 4.6 billion years ago. • Gravity pulled the densest elements to the center of the planet. • After about 500 million years, a solid crust formed on the surface.

  4. What was present on Earth? • In the atmosphere, some of the gases that were likely here were: • Water vapor (H2O) • Carbon dioxide (CO2) • Sulfur dioxide (SO2) • Sulfur dioxide (SO2) • Carbon monoxide (CO) • Hydrogen sulfide (H2S) • Hydrogen cyanide (HCN) • Nitrogen (N2) • Hydrogen (H2)

  5. Fossils

  6. Fossils • What are fossils? • Any preserved remnant of an organism

  7. Where fossils form • Most fossils form in sedimentary rock • The sediments build up until it covers the organism • Minerals replace the organic matter or fill the empty pore spaces of the organism.

  8. Dating Fossils • Relative dating is a method used to determine the age of rocks by comparing them with those in other layers.

  9. Radiometric Dating • Uses the decay of radioactive isotopes to measure the age of a rock • Radioactive isotopes that can be used for radiometric dating are found only in igneous or metamorphic rocks.

  10. The Geologic Time Scale

  11. The Geologic Time Scale • A model that expresses the major geological and biological events in Earth’s history. • The geologic time scale is divided into the Precambrian time and the Phanerozoic eon. • Eras of the Phanerozoic eon include the Paleozoic, Mesozoic, and Cenozoic eras. • Each era is divided into one or more periods.

  12. Precambrian • Nearly 90 percent of Earth’s entire history, stretching from the formation of Earth to the beginning of the Paleozoic era about 542 million years ago • Prokaryotes that photosynthesize (make their own food) enriched the atmosphere with oxygen.

  13. The Paleozoic Era • Cambrian explosion: The ancestors of most major animal groups diversified • Cambrian period • Life in the oceans continued to evolve at the end of the • Ordovician and Silurian periods • Fish, land plants, and insects appeared • Devonian period • The first tetrapods (4-limbs)

  14. The Paleozoic Era • A mass extinction ended the Paleozoic era at the end of the Permian period. • Between 60 and 75 percent of the species alive went extinct.

  15. Plate Tectonics • Plate tectonics describes the movement of several large plates that make up the surface of Earth. • These plates, some of which contain continents, move atop a partially molten layer of rock underneath them.

  16. The Mesozoic Era • Triassic period: • Mammals and dinosaurs first appeared (late in the Triassic period) • Flowering plants evolved from nonflowering plants. • Jurassic period: • Birds evolved from a group of predatory dinosaurs • About 65 million years ago, a meteorite struck Earth.

  17. Cenozoic Era • Mammals became the dominant land animals. • After the mass extinction at the end of the Mesozoic era, mammals of all kinds began to diversify.

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