Historical Methods • Counting rigs in trees – more accurate, but cannot calculate very old material.
Historical Methods • Estimating rates of erosion and sedimentation – Only useful for younger geologic features.
Historical Methods • Counting Varves – The sediments that form in bodies of water annually. (Optional) Ex. The glacial lakes deposit a like thin layer in the summer and a dark layer in the winter.
Radioactivity Radioactive Decay – the process of an atomic nucleus losses E by emitting ionizing particles and radiation. (Alpha, Beta & e- capture)
Radioactivity Radioactive Decay • Alpha Decay : An alpha particle (2 e+ and 2 e-) are emitted.
Radioactivity Radioactive Decay • Beta Decay: A neutron disintegrates into a e+ and a e- (beta particle)
Radioactivity Radioactive Decay • e- capture: A e+ captures an e- and becomes a neutron.
Radioactivity Radioactive Decay As decay continues the atom becomes an isotope of a different element. Continues until it becomes a stable (non radioactive isotope).
Radioactivity Radioactive Decay • Parent Isotope – Original element/atom • Daughter Isotope – product of the original. • Ex. C14->N14
Half Life The time it takes half an atoms radioactive material to decay to a stable product. U 238 has a half life of 4.5 b.y.
Radiometric Dating Radiometric Dating The process of measuring the amount of parent and daughter material and using the ratio to find the age of the material. (Rocks, minerals and organic material)
Radiometric Dating Radiocarbon Dating • Using C12 and C14 to date dead organisms. (not useful for organisms older than 70,000 y.o.)
Radiometric Dating Radiometric Dating • U-Pb Dating: Used to date rocks that contain U and Pb. Not acurate for rocks less than 10 myo.
Radiometric Dating Radiometric Dating • Rubidium/Strontium dating, Used to date rocks that contain Rb and Sr. Used for extremely old rocks.
Radiometric Dating Radiometric Dating • Potassium/Argon dating, Used to date rocks that contain K and Ar. Can be used to date rocks as young as 50000 y.o. Met/Sed/Ig Rocks