To indicate the age of the fossils scientist use the c-14 method. They also consider on which layer of the earth they had been found to roughly determine their age. Based on reconstruction they can identify the fossil and put it into categories. Fossils can be found in several places, you can find them on mountains that used to be covered by sea for instance. You can find ancient animals in amber. Scientists put fossils at a rather low temperature so that micro organisms won't decompose them. They also put them in places where no oxygen is present