1. HOW IS A FOSSIL FORMED? 1. Sediment 2. Layers 3. Movement 4. Erosion
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.

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

3. Relative age
Age of rocks and geologic features compared with other rocks and features nearby

4. 10.3 Absolute age dating

5. Relative vs. Absolute Age Dating
Determines ages of rocks in order that they were formed but without exact dates
Determine absolute date of the rock

6. Radiometric dating
Isotopes = atoms of the same element that have the same number of protons but different number of neutrons

7. Carbon-14 dating
Radioactive decay: Some isotopes are unstable, emit radiation and decay into “daughter” isotope
Carbon-14 is unstable isotope and decays into nitrogen-14
Over time:
The amount of “parent” isotope, carbon-14, decreases
The amount of “daughter” isotope, nitrogen-14, increases
The ratio of the two indicates the age of the rock
Half life: time required for half of parent isotope to decay into daughter isotopes
E.g. Half life of carbon 14 is approx years

8. Types of dating
Radiocarbon dating: organic material (bones, wood, charcoal)
Rock dating: living tissues replaced by minerals (e.g. U 235  Pb-207)

9. Types of dating
Radioactive dating game
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