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Eras of the Geologic Time Scale

Pgs 138 - 143. Eras of the Geologic Time Scale . Precambrian Time: 4.6bya – 540 Mya. Began with the forming of the Earth Earth’s conditions were very different from today. Atmosphere was mostly carbon dioxide, hydrogen, and nitrogen. Meteorites were crashing into the Earth’s surface.

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Eras of the Geologic Time Scale

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  1. Pgs 138 - 143 Eras of the Geologic Time Scale

  2. Precambrian Time: 4.6bya – 540 Mya • Began with the forming of the Earth • Earth’s conditions were very different from today. • Atmosphere was mostly carbon dioxide, hydrogen, and nitrogen. • Meteorites were crashing into the Earth’s surface. • Violent thunderstorms and volcanic eruptions were constant.

  3. How did life begin? • Scientists hypothesize that under these conditions, life developed from nonliving matter. • The energy present in the early Earth caused chemicals to react with one another, forming complex molecules that made life possible. • Early life was probably simple organisms that floated on ancient oceans.

  4. Life Begins • Small molecules joined together to form larger more complex molecules. • Eventually the first true cells developed called prokaryotes. • Prokaryotes lack a nucleus and did not require oxygen to survive. • They did however use carbon dioxide and gave off oxygen as a byproduct.

  5. The early changing Earth • Prokaryotes called cyanobacteria reproduced and expelled oxygen over millions of years. • Eventually, the oxygen released formed the ozone layer. • The ozone layer blocked out harmful UV radiation and allowed more diverse life to develop. • Eukaryotes (cells with a nucleus) developed over millions of years and led to more complex life.

  6. Paleozoic Era: 540Mya – 248 Mya • Paleo = ancient, zoic = life, “ancient life” • We find fossils of sponges, coral, snails, clams, squids, trilobites, and fish in this era. • Plants, fungi and air-breathing animals came onto dry land. • Forests of giant ferns, mosses and conifers covered the earth.

  7. More Paleozoic • Fossil record shows us that crawling insects were the first animals on land. • Eventually, reptiles, winged insects and cockroaches appeared. • A large mass extinction occurred at the end of the Paleozoic era • 90 % of all marine life died out.

  8. Mesozoic Era: 248 Mya – 183 Mya • Meso = middle, zoic = life: “middle life” • The age of the reptiles • Dinosaurs are the popular species known and they dominated the Earth for 150 million years. • The first birds appeared in the Mesozoic era. • Flowering plants first appeared late in the Mesozoic era

  9. The end of the Mesozoic • About 65 million years ago another mass extinction occurred. • What happened? • Meteorite? • Caused large amounts of dust and smoke. • Blocked out sunlight. • Plants died out. • Dinosaurs died out. • Global temperatures dropped. • Small mammals survived.

  10. Cenozoic Era: 65 million years ago - today • Ceno = recent, zoic = life: “recent life” • We have more fossil evidence in this era than any other era. • Mammals, birds, insects, and flowering plants appeared. • The age of mammals. • Mammals started small and grew larger and adapted to all climates.

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