1. Fossils

2. What is a fossil?
A fossil is the preserved remains of a once-living organism.

3. What do fossils tell us?
Fossils give clues about organisms that lived long ago. They help to show that evolution has occurred.
They also provide evidence about how Earth’s surface has changed over time.
Fossils help scientists understand what past environments may have been like.

4. What conditions promote fossilization?
Hard body parts such as skeletal bones or exoskeletons
Rapid burial and/or lack of oxygen

5. Erosion HOW IS A FOSSIL FORMED?
1. Sediment
An animal is buried by sediment, such as volcanic ash or silt, shortly after it dies. Its bones are protected from rotting by the layer of sediment.
2. Layers
More sediment layers accumulate above the animal’s remains, and minerals, such as silica (a compound of silicon and oxygen), slowly replace the calcium phosphate in the bones.
3. Movement
Movement of tectonic plates, or giant rock slabs that make up Earth’s surface, lifts up the sediments and pushes the fossil closer to the surface.
4. Erosion
Erosion from rain, rivers, and wind wears away the remaining rock layers. Eventually, erosion or people digging for fossils will expose the preserved remains.
Erosion
Erosion from rain, rivers, and wind wears away the remaining rock layers. Eventually, erosion or people digging for fossils will expose the preserved remains.

6. FIVE MAIN TYPES OF FOSSILS
Petrified
Fossils
Molds and
Casts
Carbon Films
Trace
Fossils
Preserved
Remains

7. What are the modes of fossil preservation ?
Unaltered
Original preservation
(original remains) - original,
unaltered material from the living organism.
material is trapped inside coating such as amber
material is trapped inside ice and tissue is preserved
Tar An organism, such as a mammoth, is trapped in a tar pit and dies. The tar soaks into its bones and stops the bones from decaying.

8. What are the modes of fossil preservation?
Altered
Mineral replacement (petrification) – pores in tissue are filled by minerals in water
Recrystallization – buried hard parts are subject to pressure over time to change to new minerals

9. More modes of fossil preservation
Carbonization – tissue material is decomposed or reduced to a film of carbon

10. Impressions- formed when the overlying sediment “compresses” the remains into a flat layer with an imprint of the organism. Even carbon is squeezed out

11. Mold – a hollowed out impression.
Cast – duplicate of the original organism.

12. trace fossils- evidence of an organism is indirect
Burrows or borings –
Spaces dug out by living things and preserved as is or filled in

13. More on trace fossils
Tracks – impressions of passage of living things, foot prints