The order of rock layers are used to determine this. It can tell scientists the order of the rock layers and events but not the exact time the fossils were formed.

Absolute Dating

Relative Dating

Radioactive Dating

Relative dating is the answer. It is the method for estimation of the age of an ancient materials by comparing it to another material's age.

Explanation:

Prior to the radioactive dating technique which could do absolute prediction of the age of any rock or event layers, this relative dating method is used by the scientists. The technique of Relative dating could tell the scientists the order of the rock layers and events. It is based on the fact that the more older the rock layer more deeper it would be. The less older rock layer would be less deeper. This procedure could not be used for absolute dating.