Hidden inside everything are atoms. They are the building blocks from which everything is made. They can help us find out how old objects are and can help us find the age of the Earth itself and even the Universe.

All atoms change or break down over time some are now stable and have stopped changing and others are still changing and are called unstable. This change can be started by chopping down a tree, hunting an animal, cooking food in a pot, a star forming or a rock solidifying. Scientists have discovered how quickly these atoms change. By measuring how much of an atom is left they can work out how along ago the change started.

Dating death

Every living thing is made of carbon. It is in our bones, the plants and animals around us and the food we eat. When all these things are alive they are constantly absorbing carbon from the atmosphere around them. When a tree is chopped down, an animal hunted or a person dies this process stops. Immediately some of the carbon begins to break down. This unstable form of carbon is called Carbon 14. Half of the Carbon 14 is lost every 5730 years. Other stable forms of carbon - Carbon 12 and Carbon 13, remain unchanged. By measuring how much Carbon 14 is left in a piece of wood, a bone or even some leather scientists can work out the date on which it died.

This technique is called Radiocarbon dating. This is a very accurate form of dating but it can be made even more precise when it is used with dendrochronology.

As old as the hills

Rocks can be unimaginably old but how can we find out exactly how old?

Being able to date rocks has been a puzzle for several hundred years, but it wasn’t until the discovery of radioactivity that answers could be found.

Many rocks contain a mineral called zircon which has traces of uranium in its structure. Uranium is a radioactive element which decays to produce helium and lead – every 704 million years half of the amount of uranium decays to these two elements. This means that over time the amount of uranium with go down and the amount of lead will go up.

Scientists can measure the amounts of uranium and lead in these zircon minerals and work out how long the uranium has been decaying.This technique is called radiometric dating and is used to find the ages of rocks, meteorites, ancient pottery and even moon rock.