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 do paleontologists know how old fossils are?

The geological time scale is used by geologists and paleontologists to measure the history of the Earth and life. It is based on the fossils found in rocks of different ages and on radiometric dating of the rocks. To get an age in years, we use radiometric dating of the rocks.

How do archaeologists determine how old something is?

Archaeologists use that assumption, called the law of superposition, to help determine a relative chronology for the site itself. Then, they use contextual clues and absolute dating techniques to help point to the age of the artifacts found in each layer.

What was the first fossil discovered?

In 1822, Mary Ann Mantell, who was married to geologist Gideon Mantell, discovered fossilized bones while on a walk in Sussex, England. Further examination found that they looked similar to an iguana skeleton, so the fossil reptile was aptly named Iguanodon.