2.3 Radiometric Dating

Question 1

What is radiometric dating?

Answer 1

1. Gives the age in millions of age for a particular specimen of rock
2. It relies on accurate measurement of minute traces of radioactive atoms
3. Atoms decay by giving out some particles and become stable

Question 2

Explain radioactive parent isotopes?

Answer 2

They spontaneously decay to form new daughter isotopes whilst releasing energy
Eg K40 potassium decays to Ar40 argon
Eg C14 carbon decays to N14 nitrogen

Question 3

Explain radioactive half life?

Answer 3

The time taken for half the number of unstable parent radioactive nuclei in a sample to decay to stable daughter elements
Eg K40 - Ar40 = 1200 million years

Question 4

Explain the carbon cycle?

Answer 4

Can only be used for living things:

1. Living organisms interact with atmosphere through respiration or photosynthesis
2. The proportion of 14C carbon in living organisms is thus the same as in the atmosphere
3. After death, 14C decays to 14N and is not replaced since the organism has stopped exchanging carbon in with the atmosphere

Question 5

When is carbon cycle useful for dating?

Answer 5

1. Used to date organic material - carbon based (peat, wood, bone etc)
2. Less than 50,000 years old - radioactive forms of carbon have short half lives - not enough 14C left to give reliable dates