Fossils

1

• Fossils

2
Fossils and Ancient Life

• Fossils are the most important source of
  information about extinct species
• Only form under certain conditions one reason
  why the fossil record is not complete

3
Types of Fossils

• Large complete organisms
• Small bacteria, pollen grains
• Fragments teeth, bits of leaf
• Trace fossils casts of footprints, tracks,
  animal droppings

4
Types of Fossils
5
Fossils in Sedimentary Rock

• Most fossils are preserved in sedimentary rock

6
What Fossils Can Reveal

• 1. Evolutionary relationships
• 2. How animals moved
• 3. Ancient environment
• 4. Ancient ecosystems

7
Relative Dating

• Relative dating places rock layers and their
  fossils into a temporal sequence (oldest on
  bottom, youngest on top)

8
Radiometric Dating

• Radiometric dating compares the amount of
  radioactive to nonreactive isotopes in a sample
  to determine its age
• Half-life time required for half of the
  radioactive atoms in a sample to decay

9
Rates of Decay

• Different radioactive elements have different
  half-lives, so they decay at different rates
• Potassium-40 1.26 billion years
• Carbon-14 5,730 years
• Potassium-42 12.4 hours