Question

which phrase describes carbon - 14 dating?
uses the rate at which nitrogen - 14 decays into carbon - 14
dates the remains of organisms to determine when they died
measures the number of unstable elements in ancient volcanic rocks
determines the age of ancient fossils older than 50,000 years old

Explanation:

Carbon - 14 dating is a radiometric dating method. It is based on the fact that living organisms take in carbon - 14 (a radioactive isotope of carbon) during their lifetime. When an organism dies, it stops taking in new carbon - 14, and the carbon - 14 in its remains begins to decay. By measuring the amount of carbon - 14 remaining in the remains of an organism, scientists can determine when the organism died.

Let's analyze each option:

• Option 1: Carbon - 14 decays into nitrogen - 14, not the other way around. So this option is incorrect.
• Option 2: This is the correct principle of carbon - 14 dating. It is used to date the remains of organisms to find out when they died.
• Option 3: Carbon - 14 dating is not used for ancient volcanic rocks. Volcanic rocks are usually dated using other radiometric dating methods such as potassium - argon dating. So this option is incorrect.
• Option 4: Carbon - 14 dating is not very accurate for fossils older than about 50,000 years because the amount of carbon - 14 remaining becomes very small and difficult to measure. So this option is incorrect.

Answer:

dates the remains of organisms to determine when they died