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Geologic Time
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A. Earth ≈ 4.6 Billion Years Old
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Billion = 4,600,000,000
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2. Most Geologic Time is divided into eras and periods
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B. Precambrian Time = 88% of Earth’s History
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1. Precambrian Earth: lava flowed over the surface – building the continents
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2. First Life. Bacteria found in rocks from 3
2. First Life? Bacteria found in rocks from 3.5 Billion Years Ago (BYA)
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3. About 2.5 BYA, bacteria started using sunlight to make their own food.
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C. The Paleozoic Era 1. began ~544 Million Years Ago (MYA)
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2. Most Paleozoic animals were invertebrates
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Cambrian Species
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3. After ~300 million years, about 95% of Earth’s species DIE due to…
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DRASTIC climate change caused by Pangaea forming (about 260 MYA)
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D. The Mesozoic Era 1. began ~245 MYA
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2. Mesozoic = Age of Dinosaurs (or Reptiles)
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Mesozoic Era
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3. Dinosaurs ruled the Mesozoic, but the first mammals also appeared in that era.
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4. Dinosaurs lived from ~225 MYA to ~65 MYA
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5. About 180 million years after the start of the Mesozoic era, a massive impact filled the sky with debris and changed the climate
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E. The Cenozoic Era 1. began ~65 MYA and continues today.
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2. Cenozoic = Age of Mammals
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3. Last Ice Age was ~10,000 years ago
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