Absolute dating Flashcards
1
Q
What does it use ?
A
Half-life or radioactive isotopes to work out age of a fossil or rock
2
Q
What is the half-life of carbon 14 ?
A
5730 years
3
Q
Where does carbon-14 come from ?
A
Produced in the atmosphere by the action of cosmic rays on nitrogen
4
Q
How is carbon-14 dating used?
A
- Plants take in carbon-14 so it is passed on through the food chain
- When an organism dies carbon 14 begins to slowly decay at a fixed rate
- Finding the ratio between carbon-14:carbon-12 can help determine the age of the fossil
5
Q
What is the ratio of Carbon-14:Carbon-12
A
1:10’12
6
Q
What are the problems with carbon-14 dating
A
- 5730 years means absolute dating is limited to 60000BP years
- Assumes the level of C-14 has been constant over time
- at least 3g of organic material is required
- samples can interact with ground water
- > dissolves C02 which can alter ratio
7
Q
What is potassium-argon dating used for ?
A
- Use to date age of volcanic rock
- can help determine age of fossil found in volcanic rock
- Ratio of potassium-40:argon-40 helps determine the age of volcanic rock
- Helps determine age of rock that is 100-200 thousand years old
8
Q
What isotopes does potassium-argon dating use ?
A
- Potassium decays into Potassium-40, Argon-40 and calcium-40
9
Q
what is the half-life of potassium-40 ?
A
- 1.25-1.3 billion years old
10
Q
what are the problems with potassium-argon dating ?
A
- available rock needs to be the same age as the fossil
- potassium-40 takes 100-200 thousand years to accumulate to sufficient quantities
- not all rock is suitable
11
Q
description and use of tree ring dating
A
- every year trees ad another growth ring of xylem
- involves counting and measuring the rings in a cross section of a tree trunk
- these are compared with tree ring sequences of known age
- can be used to adjust C-14 to C-12 ratio
12
Q
problems with tree ring dating ?
A
-Timber is rarely preserved and conditions are rare
13
Q
Relative dating and what it is used for
A
- finding out if a fossil, artefact or sedimentary layer is older or younger than others
- Used to put fossils in order of age without knowing actual age
