DATING TECHNIQUES Year 10 Biology 2015 DATING FOSSILS

DATING TECHNIQUES Year 10 Biology 2015

DATING FOSSILS • Absolute dates: actual age of the specimen in years • Relative dates: determine whether one sample is older or younger than another

STRATIGRAPHY – RELATIVE DATING • Study of layers or strata • Principle of superposition • Layers at the top are younger than the layers at the bottom • Correlation of rock strata • Matching of layers of rock from different areas

5 living fish sediment from river fish skeleton partly buried by sediment

6 more recent sediment collects older sediment becomes rock fish skeleton fossilised

7 land raised above water level recent rock older rock

8 fossilised skeleton exposed earth movements fracture rock

9 When rock strata become exposed, it can be assumed t in most cases, the lowest layers are the oldest* This means that the fossils of organisms preserved in the lowest layers represent animals and plants that lived many millions of yea rock strata of increasing age

FLUORINE RELATIVE DATING • Movement of fluoride ions in the water in the soil into the bone • All fossils in a particular deposit should contain the same amount of fluoride • The older the fossil the more fluoride it contains • Eg: Piltdown Man

INDEX FOSSILS • Index fossils: widespread & present for limited time on Earth • Examples Trilobites and Ammonites

ABSOLUTE DATING • Determining the actual age of the fossil in years • Uses Radioactive dating • Tree Rings

RADIOCARBON DATING • Decay of radioactive carbon-14 to nitrogen • C-14 produced in upper atmosphere by cosmic radiation acting on nitrogen • Decays at about the same rate • 1: 1012 (C-14: C-12) • Requires at least 3 gms of organic material

RADIOCARBON DATING • Green plants use CO 2 one atom in every million (1012) is C-14 • Plant then eaten by animal becomes part of animal • Death – intake of C-14 stops but decay of C-14 continues at fixed rate • Ratio of C-14 to C-12

HALF-LIFE OF C-14 Over a period of 5730 30 years half of any given quantity of C-14 breaks down. HALF LIFE OF C-14

PROBLEMS WITH C-14 • After 70, 000 years amount of C-14 becomes negligible • Material must be organic (contain carbon) • Assumption that ratio of C-14: C-12 was constant – now know that it varies

TREE RING DATING • Concentric rings on the surface of a cut tree • Each ring is one year • Rings width varies according to favourable conditions • Marker rings correlated with timber from ancient human structures

Tree-ring Dating

WHAT NOW? • Read pages 48 – 52 • Answer questions page 53 Q 1 – 13…