Biology 2015 Dating Techniques 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 ID: 289107
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Slide1
Year 10Biology2015
Dating TechniquesSlide2
DATING FOSSILS
Absolute dates
: actual age of the specimen in years
Relative dates
: determine whether one sample is older or younger than anotherSlide3
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
areasSlide4
living fish
sediment from river
fish skeleton partly buried by sediment
5
SedimentationSlide5
fish skeleton fossilised
older sediment
becomes rock
more recent sediment collects
6
Layers of sedimentSlide6
land raised above
water level
recent rock
older rock
7
Earth’s crust movementSlide7
earth movements
fracture rock
fossilised skeleton exposed
8
Fractured rockSlide8
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
9
Rock strataSlide9
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 ManSlide10Slide11
INDEX FOSSILS
Index fossils
: widespread & present for limited time on
Earth
Examples Trilobites and AmmonitesSlide12Slide13
ABSOLUTE DATING
Determining the actual age of the fossil in years
Uses Radioactive dating
Tree RingsSlide14
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
1:10
12
(C-14:C-12)
Requires at least 3
gms of organic materialSlide15
Radiocarbon Dating
Green plants use CO
2
one atom in every million
million
(10
12
) is C-14
Plant then eaten by animal becomes part of animalDeath – intake of C-14 stops but decay of C-14 continues at fixed rate
Ratio of C-14 to C-12 Slide16Slide17
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-14Slide18
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 variesSlide19
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 structuresSlide20Slide21
Tree-ring DatingSlide22
WHAT NOW?
Read pages 48 – 52
Answer questions page 53 Q 1 – 13…