Geologists measure the abundance of these radioisotopes instead to date rocks.Materials that originally came from living things, such as wood and natural fibres, can be dated by measuring the amount of carbon-14 they contain.
The carbon-14 it contained at the time of death decays over a long period of time, and the radioactivity of the material decreases.
The approximate time since the organism died can be worked out by measuring the amount of carbon-14 left in its remains compared to the amount in living organisms.
There is a small amount of radioactive carbon-14 in all living organisms because it enters the food chain.
Once an organism dies, it stops taking in carbon-14.
Radiocarbon dating is a method of estimating the age of organic material.
It was developed right after World War II by Willard F.
Once the organism dies, it stops replenishing its carbon supply, and the total carbon-14 content in the organism slowly disappears.
Scientists can determine how long ago an organism died by measuring how much carbon-14 is left relative to the carbon-12.
Because of the short length of the carbon-14 half-life, carbon dating is only accurate for items that are thousands to tens of thousands of years old. Geologists must therefore use elements with longer half-lives.
For instance, potassium-40 decaying to argon has a half-life of 1.26 billion years and beryllium-10 decaying to boron has a half-life of 1.52 million years.
Carbon-14 has a half life of 5730 years, meaning that 5730 years after an organism dies, half of its carbon-14 atoms have decayed to nitrogen atoms.