Boxi Learn › History › Stage 3 · Structure and Evidence
How old is it? Tree rings and radiocarbon
HIS-2 How do we know about the past?X-2 Evidence outweighs opinion
What many people think
Scientists just guess how old ancient things are.
The idea
Carbon-14 in once-living things halves about every 5,730 years, so what is left works like a clock; tree rings, counted year by year, check and calibrate that clock.
Explain it
A friend says “archaeologists just guess the age of bones and charcoal.” Explain, with one number from this page, how the carbon-14 clock works and why tree rings are needed to check it.
Try at home
Look at a tree stump or a log end. Count the rings from bark to centre, and find the narrow ones. Then take 64 coins, shake them in a box and remove the tails; repeat. How many shakes until about 1/4, 1/16 are left?