Transcript Fossils ppx
Fossils Evidence of ancient life 4 categories of fossils: 1. Original remains 2. Casts and molds 3. Replacement by minerals 4. Indirect evidence 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 2. Casts and Molds Mold – impression of the organism or shell Cast – minerals fill the mold and harden in the shape of the organism 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 Ex: petrified wood 4. Indirect evidence: • Footprints, tracks, nests, burrows, coprolites 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 The fossil record is incomplete: • Not all organisms will fossilize. • Fossils have been destroyed. • The quality of fossils varies. 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 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. 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. 4. Lower layers show a small, horselike 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. 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. Superposition: Fossil Correlation: