Geologic Time Scale Chapter 9, Section 3 Measuring Time The Earth has existed for 4.6 billion years The Earth has existed for 4.6 billion years The

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  • Geologic Time ScaleChapter 9, Section 3

  • Measuring TimeThe Earth has existed for 4.6 billion years

    The geologic time scale divides all those years into sections

    Each section shows a specific change in life or in the Earths surface

  • Giving Time a NameThe largest sections are called eonsEons are divided into eras (the 2nd largest section)Eras are divided into periodsThen periods are divided into epochsUsually 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 Earths history mark the boundaries between the sectionsMost sections have been divided because a major organism developed or went extinct.

  • ExtinctionExtinction = the death of every member of a species

    It can happen because the environment changed, and some organisms could not survive in the new environment.

  • Mass ExtinctionMass 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)

  • Lets Talk About the Eras

  • Precambrian Time

  • Precambrian TimeTime from the formation of the Earth (4.6 billion years ago) to 542 million years agoThe Earth was very different thenAt first, there was no oxygen or living thingsThen the first organisms appeared in the oceans 3.6 billion years ago

    They were called Prokaryotes

  • ProkaryotesOnly one cell and no nucleusOne type, Cyanobacteria, were the first organisms on EarthThrough photosynthesis, they released oxygen into the airAs oxygen began to build up, the ozone was formedThe ozone protects the Earth against the suns harmful rays (deadly to land organisms)Now organisms could live on land too!

  • EukaryotesAfter another 1 billion years, more complex organisms developedThey were called EukaryotesMany cells with a nucleusEvolved into organisms on Earth today

  • Paleozoic EraBegan 542 million years ago and ended 251 million years ago

    Many new life forms appeared during the 1st 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 ExtinctionThe 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 EraBegan 251 million years agoSurviving reptiles and amphibians evolved into many other species (like dinosaurs) = Age of Reptiles

  • Cretaceous-Tertiary ExtinctionAnother mass extinction happened 65 million years ago Marked the end of the Mesozoic Era and the beginning of the Cenozoic EraAll of the dinosaurs and half of the other animals & plants went extinctScientists think an asteroid hit Earth, the dust clouds blocked out the sun, plants died, then herbivores, then carnivores.

  • Cenozoic Era

  • Cenozoic EraBegan 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?


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