Dating Rocks & Fossils

Dating Rocks & Fossils

Will you go out

with meNO!

I’m far too old for you!

Relative dating

• The nearer the surface a stratum of rock is, the younger the fossils it contains.

• The age of a fossil can be estimated if you can accurately date rock strata above and/or below

• “Index fossils” dated at one site may be used to estimate ages of fossils found at another site

Radiometric techniques

Carbon dating• Living things take in some C-14 which is

produced at a (nearly) steady rate in the upper air.

• C-14 decays to C-12 at a constant rate.• By measuring how much C-14 is left in a

once living thing we can find ages up to about 50,000 years

Radiometric techniques (cont’d)Potassium – Argon dating• When rock melts it loses all the gas it

contains. • Once it cools, potassium-40 in the lava

decays radioactively at a known rate to form argon-40 gas.

• By measuring the amount of Ar-40 in volcanic rock, ages from over 10,000 to millions of years can be found.

Radiometric techniques (cont’d)

Uranium series decay• Using uranium’s decay to other elements it

is possible to date corals and shells up to about 1 million years.

Fission track• Tracks left in volcanic rock, glass or

pottery by radioactive decay of uranium can be used to find ages from 1000 years to 100 million years.

Electron Spin Resonance (ESR)

• Electronic charges produced by radioactivity in surrounding rocks can be trapped in a fossil such as teeth or bones

• The older the fossil the more charges in it. This can be measured by ESR spectroscopy

Genome Analysis• DNA sequencing: The more similar the DNA

of 2 species/groups, the more closely they are related

• Mitochonrial DNA (mtDNA). Passed on from mother only. Mutations occur at a steady rate so it can show how closely groups are related and how long ago they separated.

• Y chromosome DNA. Passed on from father to sons only. Not prone to much change so can be used to trace ancestry and relationships..