Geologic time scale


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Geologic time scale

  1. 1. Geologic Time Scale Chapter 9
  2. 2. Measuring Time <ul><li>The Earth has existed for 4.6 billion years </li></ul><ul><li>The geologic time scale divides all those years into sections </li></ul><ul><li>Like how your science book is divided into Units, then Chapters, then Sections, then Pages </li></ul><ul><li>Each section is unique because it shows a specific change in life or in the Earth’s surface </li></ul>
  3. 3. Giving Time a Name <ul><li>The largest sections are called “eons” </li></ul><ul><li>“ Eons” are divided into “eras” (the 2 nd largest section) </li></ul><ul><li>“ Eras” are divided into “periods” </li></ul><ul><li>Then “periods” are divided into “epochs” </li></ul><ul><li>Usually the oldest sections are shown on the bottom and the most recent sections are shown on the top </li></ul>
  4. 4. How is Time Divided? <ul><li>Major changes in Earth’s history mark the boundaries between the sections </li></ul><ul><li>Most sections have been divided because a major organism developed or went extinct. </li></ul>
  5. 5. Extinction <ul><li>Extinction = the death of every member of a species </li></ul><ul><li>It can happen because of competition between the species, so some organisms ran out of food or space </li></ul><ul><li>It can happen because the environment changed, and some organisms could not survive in the new environment. </li></ul>
  6. 6. Mass Extinction <ul><li>Mass extinction = the extinction of many species at the same time </li></ul><ul><li>Can you think of an example of a mass extinction? </li></ul><ul><li>It can be caused by gradual changes in climate or ocean currents (Uniformitarianism) </li></ul><ul><li>Or by catastrophic events, like an asteroid hitting the earth and blocking out the sun (Catastrophism) </li></ul>
  7. 7. Let’s Talk About the Eras
  8. 8. Precambrian Time
  9. 9. Precambrian Time <ul><li>Time from the formation of the Earth (4.6 billion years ago) to 542 million years ago </li></ul><ul><li>The Earth was very different then </li></ul><ul><li>At first, there was no oxygen or living things </li></ul><ul><li>Then the first organisms appeared in the oceans 3.6 billion years ago </li></ul><ul><li>They were called Prokaryotes </li></ul>
  10. 10. Prokaryotes <ul><li>Only one cell and no nucleus </li></ul><ul><li>One type, Cyanobacteria, were the first organisms on Earth </li></ul><ul><li>Through photosynthesis, they released oxygen into the air </li></ul><ul><li>As oxygen began to build up, the ozone was formed </li></ul><ul><li>The ozone protects the Earth against the sun’s harmful rays (deadly to land organisms) </li></ul><ul><li>Now organisms could live on land too! </li></ul>
  11. 11. Eukaryotes <ul><li>After another 1 billion years, more complex organisms developed </li></ul><ul><li>They were called Eukaryotes </li></ul><ul><li>Many cells with a nucleus </li></ul><ul><li>Evolved into organisms on Earth today </li></ul>
  12. 12. Paleozoic Era <ul><li>Began 542 million years ago and ended 251 million years ago </li></ul><ul><li>Divided into 6 periods </li></ul><ul><li>Many new life forms appeared during the 1 st period, the Cambrian Period = “Cambrian Explosion” </li></ul><ul><li>For the first time on Earth, organisms had hard parts (shells, exoskeletons) </li></ul><ul><li>Some organisms that were alive during this period still exist today (ferns and salamanders) but they were giants! </li></ul>
  13. 13. Permian Extinction <ul><li>The largest mass extinction happened 251 million years ago </li></ul><ul><li>Marked the end of the Paleozoic Era and the start of the Mesozoic Era </li></ul><ul><li>Scientists are not sure what caused this mass extinction (maybe climate change & volcanoes) </li></ul><ul><li>90% of ocean life and 78% of land life died </li></ul><ul><li>Reptiles and amphibians survived! </li></ul>
  14. 14. Mesozoic Era
  15. 15. Mesozoic Era <ul><li>Began 251 million years ago </li></ul><ul><li>Surviving reptiles and amphibians evolved into many other species (like dinosaurs) = “Age of Reptiles” </li></ul>
  16. 16. Cretaceous-Tertiary Extinction <ul><li>Another mass extinction happened 65 million years ago </li></ul><ul><li>Marked the end of the Mesozoic Era and the beginning of the Cenozoic Era </li></ul><ul><li>All of the dinosaurs and half of the other animals & plants went extinct </li></ul><ul><li>Scientists think an asteroid hit Earth, the dust clouds blocked out the sun, plants died, then herbivores, then carnivores. </li></ul>
  17. 17. Cenozoic Era
  18. 18. Cenozoic Era <ul><li>Began 65 million years ago and continues today </li></ul><ul><li>Scientists know the most about this Era because the fossils are in the top rock layers and are easier to find </li></ul><ul><li>Land & climate has changed a lot </li></ul><ul><li>What big change will happen that will end this era & start the next? </li></ul>