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Understanding the Formation and Age of Earth: Geological Time Scale Overview

The Earth formed approximately 4.6 billion years ago, a date established through the study of rock layers and fossils, aided by radioactive dating techniques. The geological time scale divides Earth's history into eras and periods, with the Precambrian being the longest at its inception 4.6 billion years ago and concluding 544 million years ago. Key events in early Earth included the formation of oceans, atmosphere, and continents from volcanic eruptions and comet impacts. The earliest forms of life likely resembled modern bacteria, paving the way for an oxygen-rich atmosphere through photosynthesis.

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Understanding the Formation and Age of Earth: Geological Time Scale Overview

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  1. P337\Section 4 Geologic Time Scale

  2. 1a How long ago did the Earth form? • 4.6 billion years ago

  3. Summarize the process by which scientists determined the age of Earth. • Scientists studies rock layers and fossils worldwide and placed Earth’s rock layers in order by relative age. Later, radioactive dating helped them determine the absolute ages of the divisions.

  4. What are the basic units into which the geologic time scale is divided? • The geologic time scale is divided into eras and periods.

  5. Study figure 14. (p336) Which major division of time was the longest? • Precambrian • When did it begin? • 4.6 BYA • When did it end? • 544 MYA

  6. Place the following in the correct order from earliest to latest: Tertiary, Jurassic, Quaternary, Triassic, and Cretaceous. • Triassic, Jurassic, Cretaceous, Tertiary, and Quaternary

  7. Section 5 Early Earthp. 341e • 1a How long ago did the Earth form? • The Earth formed about 4.6 billion years ago

  8. Summarize the process by which scientists determined the age of the Earth. • Scientists used radioactive dating of rocks from Earth and moon to determine the age of the Earth.

  9. What physical features formed during Earth’s first several hundred million years? • Oceans, the atmosphere, and continents were formed.

  10. How did volcanic eruptions and comets change early Earth? • Volcanic eruptions released carbon dioxide into the atmosphere, and comets released water vapor.

  11. What caused water erosion to begin on Earth’s surface? • Rain

  12. What do scientists think were the first organisms to evolve on Earth? • Organisms similar to our present day bacteria were probably the first life forms.

  13. How would Earth’s atmosphere be different if organisms capable of photosynthesis had not evolved? • The Earth’s atmosphere would have little or no oxygen. A by-product of photosynthesis is oxygen.

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