1. Radiometric Dating (pg 8)
TRILOBITE - early arthropod - EXTINCT!

2. • Fossil - preserved remains of ancient life
- found in sedimentary rock
- studied by paleontologists

3. • Sedimentary rock - formed as small particles
settle on bottom of ocean, lake or river

4. • Older rock layers usually deeper in earth

5. • Fossils form as organic material replaced by
minerals (petrified)

6. • Relative dating - places rock layers in a
temporal sequence based on depth

7. • Absolute dating: Gives a rock layers age in
years
• Radiometric Dating - dates rock based on
decay of radioactive isotopes.
• Radioactive isotopes (such as Carbon-14 and
Potassium-40) break down at a steady rate.

8. Isotopes
• Radioactive isotopes contain extra neutrons,
making them unstable
• For example, normal carbon (C-12) contains 6
protons and 6 neutrons. Radioactive C-14
contains 6 protons and 8 neutrons
• Over time, Carbon-14 decays, becoming
Nitrogen-14

9. • Half life =Amountof time for half of isotope to
decay
• K-40 = 1.3 billion years
• C-14 = 5,730 years

10. • Scientists measure amount of remaining
radioactive isotope and compare it to original
amount to age rocks and fossils
• Ex) Potassium-40  Argon-40
• Argon gas gets trapped in the rock