A team digs up a wooden tool. A laboratory finds that it has one eighth of the carbon-14 that a…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A team digs up a wooden tool. A laboratory finds that it has one eighth of the carbon-14 that a living tree has. The half-life of carbon-14 is 5730 years.
- How many half-lives have passed?
- How old is the tool?
- A second tool is 11460 years old. What percentage of its original carbon-14 is left?
Need a reminder? The key ideaShow
Homologous organs have the same origin and different jobs (divergent evolution). Analogous organs have the same job and different origins (convergent evolution). Deeper rock layers are older. Radioactive carbon halves every years, so after half-lives is left.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. One eighth is left. The half-life is years.
Plan. Count the halvings, then multiply by the half-life.
Step 1. (a) . That is half-lives.
Step 2. (b) Age: years.
Step 3. (c) half-lives. The amount left is , which is per cent.
Answer: half-lives; years; per cent.
Check. The fraction , so the first answer agrees.
Watch out. Carbon-14 works only for remains of living things, up to about 50000 years old. It cannot date a dinosaur bone.
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