29.3 A BSOLUTE T IME. H ISTORICAL M ETHODS Counting rigs in trees – more accurate, but cannot calculate very old material.

29.3 ABSOLUTE TIME

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 DecayAs 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 DatingThe 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