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Fossils
Mr. SkirbstEarth Science
Topic 24
Fossils
The preserved remains or evidence of a living thing
Types of Fossils1. Petrification
Types of Fossils1. Petrification
minerals replace organic material
Ex. Petrified wood
Types of Fossils2. Molds
Types of Fossils2. Molds
empty space left by plant of animal buried in sediment
Types of Fossils2. Molds
empty space left by plant of animal buried in sediment
3. Casts
Types of Fossils2. Molds
empty space left by plant of animal buried in sediment
3. Castsa filled in mold
Types of FossilsMolds & Casts
CAST
MOLD
Types of Fossils4. Imprints
Types of Fossils4. Imprints
impression in soft sediment
Types of Fossils5. Preservation
Types of Fossils5. Preservation
entire specimen preserved (hard and soft parts)
Types of Fossils5. Preservation
entire specimen preserved (hard and soft parts)
Freezing – trapped in ice
Types of Fossils5. Preservation
entire specimen preserved (hard and soft parts)
Freezing – trapped in iceAmber – trapped in sap
Types of Fossils5. Preservation
entire specimen preserved (hard and soft parts)
Freezing – trapped in iceAmber – trapped in sapTar pit – trapped in tar
Types of Fossils5. Preservation
entire specimen preserved (hard and soft parts)
Freezing – trapped in iceAmber – trapped in sapTar pit – trapped in tarPeat pit – trapped in peat / bog
Types of Fossils6. Trace Fossils
Types of Fossils6. Trace Fossils
tracks, trails, footprints
Age of Fossils
Age of Fossils1. Relative Age:
Age of Fossils1. Relative Age:
- determining age “relative” to others
Age of FossilsLaw of Superposition
Age of FossilsLaw of Superposition
in sedimentary rock layers, older rocks are beneath younger rocks
Age of FossilsLaw of Superposition
YOUNG
OLD
Age of FossilsIndex Fossils
Age of FossilsIndex Fossils
- layers of rock with index fossils are close in age to other layers with the same kind of fossils
Age of FossilsIndex Fossils
1
1
2
2
3
3
4
Age of Fossils2. Absolute Age
Age of Fossils2. Absolute Age
determining the “actual” age of fossils
Age of FossilsRadioactive Dating
Age of FossilsRadioactive Dating
- radioactive elements decay at a constant rate
Age of FossilsRadioactive Dating
- radioactive elements decay at a constant rate
Half-life – time it takes for ½ of element to decay
