Absolute dating

Question 1

What does it use ?

Answer 1

Half-life or radioactive isotopes to work out age of a fossil or rock

Question 2

What is the half-life of carbon 14 ?

Answer 2

5730 years

Question 3

Where does carbon-14 come from ?

Answer 3

Produced in the atmosphere by the action of cosmic rays on nitrogen

Question 4

How is carbon-14 dating used?

Answer 4

• 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

Question 5

What is the ratio of Carbon-14:Carbon-12

Answer 5

1:10’12

Question 6

What are the problems with carbon-14 dating

Answer 6

• 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

Question 7

What is potassium-argon dating used for ?

Answer 7

• 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

Question 8

What isotopes does potassium-argon dating use ?

Answer 8

• Potassium decays into Potassium-40, Argon-40 and calcium-40

Question 9

what is the half-life of potassium-40 ?

Answer 9

• 1.25-1.3 billion years old

Question 10

what are the problems with potassium-argon dating ?

Answer 10

• 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

Question 11

description and use of tree ring dating

Answer 11

• 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

Question 12

problems with tree ring dating ?

Answer 12

-Timber is rarely preserved and conditions are rare

Question 13

Relative dating and what it is used for

Answer 13

• 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