Todays knowledge of fossil ages comes primarily from radiometric dating, also known as radioactive dating. Radiometric dating relies on the properties of isotopes. These are chemical elements, like carbon or uranium, that are identical except for one key feature -- the number of neutrons in their nucleus.

How do we know how old the fossils are?

To establish the age of a rock or a fossil, researchers use some type of clock to determine the date it was formed. Geologists commonly use radiometric dating methods, based on the natural radioactive decay of certain elements such as potassium and carbon, as reliable clocks to date ancient events.

How old is the bone I found?

Archaeologists unearthed the bones of at least five people at Jebel Irhoud, a former barite mine 100km west of Marrakesh, in excavations that lasted years. They knew the remains were old, but were stunned when dating tests revealed that a tooth and stone tools found with the bones were about 300,000 years old.

How can you tell if a bone is a human or animal?

The major difference between human and non- human animal bone structure therefore principally relates to density. Non- human animal bones have a greater density relative to size; they are less porous and are thicker in cross section than the bones of humans.