1. Dating Techniques
Year 10
Biology
2015

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

3. 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

4. 5 living fish sediment from river
fish skeleton partly buried by sediment
Sedimentation

5. 6 more recent sediment collects older sediment becomes rock
fish skeleton fossilised
Layers of sediment

6. Earth’s crust movement7
land raised above
water level
recent rock
older rock
Earth’s crust movement

7. 8 fossilised skeleton exposed earth movements fracture rock
Fractured rock

8. When rock strata become exposed, it can be assumed that, 9
When rock strata become exposed, it can be assumed that,
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 years ago
rock strata of
increasing age
Rock strata exposed at a cliff face. Each layer represents millions of years of deposition.
* The movements of the Earth’s crust may cause the strata to become distorted. Sometimes the strata are vertical or even turned upside down with the oldest rocks appearing on top. It is usually possible to tell when this has happened.
Rock strata

9. 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

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

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

14. Decay of radioactive carbon-14 to nitrogen
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

15. Green plants use CO2 one atom in every million million (1012) is C-14
Radiocarbon Dating
Green plants use CO2 one atom in every million 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

17. 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

18. 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

19. 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

21. Tree-ring Dating

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