Geologic time scale
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Geologic time scale






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Geologic time scale Geologic time scale Presentation Transcript

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