Scientists know how long it takes for half of a given quantity of carbon-14 to decay — a length of time called a half-life. While radiocarbon dating is useful only for materials that were once alive, scientists can use uranium-thorium-lead dating to measure the age of objects such as rocks.

How do we know how old something is using carbon dating?

Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.

How do they determine how old bones are?

Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages. Absolute dating is used to determine a precise age of a fossil by using radiometric dating to measure the decay of isotopes, either within the fossil or more often the rocks associated with it.

How old did the carbon dating say the bone was?

The bone was 68 million years old, and conventional wisdom about fossilization is that all soft tissue, from blood to brains, decomposes. Only hard parts, like bones and teeth, can become fossils.