FossilsEvidence of ancient life

4 categories of fossils:

1. Original remains2. Casts and molds3. Replacement by minerals4. 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 MoldsMold – 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 climateFossils 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: