Absolute Dating (2)

Question 1

What isotope is Carbon-14 based on?

Answer 1

decay of radioactive isotope of carbon (carbon-14) to nitrogen

Question 2

What is half life C^14

Answer 2

5730 years

Question 3

Where and how is C14 produced?

Answer 3

produced in the upper atmosphere
by the action of cosmic radiation on nitrogen at about the same rate at which it decay

Ratio of 1 Carbon-14 to 1012 Carbon-12

Question 4

How are atmospheric 14C incorporated into organic molecules?

Answer 4

Atmospheric 14C is incorporated into organic molecules by plants during photosynthesis

Animals get 14C from the plants they eat

Question 5

Describe the ratio of C12 and C14 ratio.

Answer 5

While an organism is alive the C12-C14 ratio is constant.

When it dies, there is no more intake of carbon and we see the decay of the C14.

By measuring the ratio of C12 to C14 the age of the specimen can be estimated.

Question 6

List problems with carbon-14 dating.

Answer 6

Assumes that the rate of carbon 14 production (and hence the amount of cosmic rays striking the Earth) has been constant

Can only be used on organic (once living / carbon-containing) material

Cannot be used beyond 60,000 years since the amount of C14 is too small to measure.

It requires at least 3 grams of organic material

This can be overcome with accelerator mass spectrometry (AMS) radiocarbon dating which requires samples of 100mg only