Fossils

Absolute Dating

Actual age of fossil

Relative Dating

Whether fossil is older/younger than another

Fossils

Preserved remains/traces of previously living organism

Conditions Required

Quick burial by sediment - reduce environmental damage & scavenging

Alkaline soil - acidic dissolves

Low O2 environment - less decomposition + decay organisms

Minerals replace organic matter

Long period of stability

WHY is fossil record imcomplete?

Rare - conditions do not always occur

Small proportion discovered

Accurate dating difficult

Controversy - different predictions/interpretations of fragments/reconstructions

Artefacts

Man made objects - indicate culture/lifestyle/activities

Artefacts Examples

Beads

Stone tools

Carvings

Cave paintings

Potassium Argon Dating

Decay of potassium-40 to argon-40

Potassium Argon Process

Ratio of K to Ar in rock

Determine age of rock

Half life - 1.3 billion

Limitations - Potassium Argon

Cannot date rock younger than 200,000 yrs

Cannot date fossils

Carbon-14 Dating

Decay of radioactive carbon-14 to nitrogen

Process Carbon-14

Organism dies - stop carbon-14 intake

Ratio of carbon-14 to carbon-12

Half life - 5730 yrs

Limitations Carbon-14

Cannot date fossils older than 60,000 yrs

Must contain organic compounds

Principle of Superposition

Assume rock layers above are younger than layers below

Correlation of Rock Strata

Matching rock layers from different areas

Assume same fossils = same age

Index Fossils

Widespread fossils that were present for short period - precise dating

Stratigraphy Limitations

Dynamic strata - faulting/folding Earth’s crust change layers

Bury dead - appear older