• Fossils form as organic material replaced by minerals (petrified)
• Relative dating - places rock layers in a temporal sequence based on depth
• 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.
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
• Half life =Amountof time for half of isotope to decay• K-40 = 1.3 billion years• C-14 = 5,730 years
• 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