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:

• Option 1: Carbon - 14 dating is about carbon - 14 decaying, not nitrogen - 14 decaying into carbon - 14. So this is incorrect.
• Option 2: Carbon - 14 is present in living organisms. When an organism dies, the carbon - 14 in it starts to decay at a known rate. By measuring the remaining carbon - 14 in the remains of the organism, we can determine when it died. This is the correct description of carbon - 14 dating.
• Option 3: Carbon - 14 dating is used for organic remains, not for measuring unstable elements in volcanic rocks (which are inorganic and often dated using other methods like potassium - argon dating). So this is incorrect.
• Option 4: Carbon - 14 has a half - life that limits its effective dating range to around 50,000 years or less. So it can't be used to date fossils older than 50,000 years. This is incorrect.

Answer:

dates the remains of organisms to determine when they died