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

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, 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.

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: