fossils evidence of ancient life. 4 categories of fossils: 1. original remains 2. casts and molds 3....
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FossilsEvidence of ancient life
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4 categories of fossils:
1. Original remains2. Casts and molds3. Replacement by minerals4. Indirect evidence
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1. Original remains
• Actual bones, teeth, or pollen grains
• Whole insects that were trapped in sap and hardened into amber
• Wooly mammoth frozen in ice
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2. Casts and MoldsMold – impression of the organism or shell
Cast – minerals fill the mold and harden in the shape of the organism
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3. Replacement by minerals
• Organic matter decays, cell by cell, and is replaced by minerals from the groundwater
• The minerals harden to stone in the exact shape of the original organism
Ex: petrified wood
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Ex: petrified wood
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4. Indirect evidence:• Footprints, tracks, nests, burrows, coprolites
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What can we learn from fossils?
1. Where the organism lived.2. When they lived and when they became
extinct.3. What the environment was like.
• Shells indicate a shallow sea• Plant types would indicate climate
Fossils are evidence of evolution
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The fossil record is incomplete:
• Not all organisms will fossilize.• Fossils have been destroyed.• The quality of fossils varies.
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What you learn from the following…
1. In a layer of shale, you find the bones of horses, antelope, and an elephant-like animal.
The area was a grassland
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2. A cliff shows a dozen or more layers, covering many millions of years of time. Each layer contains a different fossil group.
As environmental changes occurred, new organisms moved into the area or evolved and adapted.
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3. The lower layers of a cliff have fossils of sea life. The middle layers have horse fossils and grass seeds. The top layers contain coal.
The area dried out over time.
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4. Lower layers show a small, horse-like animal with three-toed feet. The upper layers show similar but larger animals with one toe on each foot.
This demonstrates the evolution of the horse. It was originally a fox sized animal living in the forest. As the ground became drier and harder, the horse developed stronger legs and hooves.
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Relative dating of rocks and fossils:determining which layers are older and which are younger.
• Law of Superposition: the oldest is on the bottom, dikes and sills are younger than the layers they cut across.
• Fossil Correlation: rocks from different areas with the same fossils are the same age.
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Superposition:
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Fossil Correlation:
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