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Fossils and Geologic Time. Early History of Earth. Hot interior and surface Volcanoes released gases Water vapor Carbon dioxide Nitrogen Mot much oxygen First organisms 3.9 billion years ago. Fossils – Clues to the Past. A fossil is evidence of an organism that lived long ago.
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Early History of Earth Hot interior and surface Volcanoes released gases Water vapor Carbon dioxide Nitrogen Mot much oxygen First organisms 3.9 billion years ago
Fossils – Clues to the Past A fossil is evidence of an organism that lived long ago. trace cast petrified imprint mold amber
Fossils – Clues to the Past How do fossils form? Animal or plant covered in mud or sand Minerals seep into the body Pressure turns mud or sand into rock
Fossils – Clues to the Past How do we know how old fossils are? 1. Relative dating – Rock forms in layers Younger layers at top Tells us which fossils are older or younger
Fossils – Clues to the Past How do we know how old fossils are? 2. Radiometric Dating – Rocks have radioactive isotopes – unstable atoms that break down over time We know how long it takes to break down Absolute age
Geologic Time Scale A calendar of Earth’s history based on fossils 66 mya--- 245 mya--- 544 mya---
Geologic Time Scale Precambrian Until 544 million years ago Unicellular prokaryotes Multicellular eukaryotes 66 mya--- 245 mya--- 544 mya---
Geologic Time Scale Paleozoic 544 to 245 million years ago Fish, land plants, amphibians, reptiles Ends with mass extinction 66 mya--- 245 mya--- 544 mya---
Geologic Time Scale Mesozoic 245 to 66 million years ago Small mammals, dinosaurs, birds Mass extinction 66 mya--- 245 mya--- 544 mya---
Geologic Time Scale Cenozoic 66 million years ago to today Mammals 66 mya--- 245 mya--- 544 mya---
Continental Drift Pangaea 245 million years ago Breaks up 135 million years ago Moving apart 66 million years ago