P4e

Question 1

How can you work out the age of rocks and fossils?

Answer 1

• radioactive dating

- by using the amount of radioactive isotope left in a sample, and knowing its half-life

Question 2

How does radiocarbon dating work?

Answer 2

• carbon-14 is an isotope of carbon found scarcely in the air and living things
• when living things die, they stop exchanging gases with air outside and carbon-14 is tapped inside
• it gradually decays
• by measuring the proportion of carbon-14 left in something old, can tell you how long ago the item was living material using the known half-life

Question 3

What are the relative proportions of uranium and lead at certain times?

Answer 3

• initially: 100% uranium, 0% lead (ratio of uranium to lead 1:0)
• after one half-life: 50% uranium, 50% lead (ratio of uranium to lead 1:1)
• after two half-lives:25% uranium, 75% lead (ratio of uranium to lead: 1:3)

Question 4

How do uranium isotopes form isotopes of lead?

Answer 4

-uranium isotopes have very long half-lives and decay to via a series of short-lived particles to produce stable isotopes of lead

Question 5

How can rocks be dated?

Answer 5

-using the relative proportions of uranium and lead in a sample of rock, and using the known half-life of uranium