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An equilibrium is reached whereby about one in a trillion carbon atoms in the atmosphere is carbon-14.
Carbon-14 in living things decays all the time but is replaced by carbon-14 in food. In fact, all living things are rearranged food and NOTHING else.
We can use the same idea to find out how long it would take for a sample with radioactivity 120 Bq to drop to 30 Bq. We can use radioactive decay to calculate the age of things.
The best-known technique is called ‘radiocarbon dating’ or just 'carbon dating'.
We’ll also see how carbon dating can be used to date ancient remains. If we had a bigger sample of the same isotope then the count would be higher, say 200 becquerels. Then we halve the count for each half-life: 100 Bq after 10 years; 50 Bq after 20 years; 25 Bq after 30 years So we can see the radioactivity would be 25 becquerels afer 30 years.Animals and plants have similar amounts of radioactive isotopes, particularly potassium-40, another beta emitter.