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
