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Earth’s History

Earth’s History. The Earth formed from a mass of dust and gas about ____ years ago. 4.6 billion years ago. The earliest life forms were probably similar to present day ________. Bacteria. Paleontologists call the beginning of the Paleozoic era the “Cambrian Explosion” because.

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Earth’s History

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  1. Earth’s History

  2. The Earth formed from a mass of dust and gas about ____ years ago.

  3. 4.6 billion years ago

  4. The earliest life forms were probably similar to present day ________.

  5. Bacteria.

  6. Paleontologists call the beginning of the Paleozoic era the “Cambrian Explosion” because

  7. So many life forms appeared within a relatively short period of time

  8. The first vertebrates were

  9. Jawless fish

  10. The first vertebrate to crawl onto land was the

  11. lungfish

  12. An amphibian is an animal that

  13. Lives part of its life on land and part of its life in water

  14. At the end of the Paleozoic there was a mass extinction. __________ of life in the oceans disappeared. (Give your answer as a percentage)

  15. 95%

  16. The Mesozoic Era is known as the “Age of ________”

  17. Age of Reptiles or Age of Dinosaurs

  18. Birds first appeared during the _________ period.

  19. Jurassic

  20. About ________ years ago at the end of the Cretaceous Period, a mass extinction occurred.

  21. 65 million years ago

  22. The extinction of the dinosaurs created an opportunity for ___________

  23. mammals

  24. The fossil record suggests that human ancestors appeared about _______ years ago.

  25. 3.5 million

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