Different fossils species that occur together constitute a fossil assemblage.
It may surprise you to learn that geologists were able to determine much of the history of the Earth and its life without knowing anything about the actual ages of the rocks that they studied. At location A, layers 1 and 2 were deposited. If the layers are horizontal and traceable over considerable distances, the geologist will conclude unless evidence to the contrary turns up that there is a very high probability that the layers are right-side-up. Putting this all together, we can determine the relative ages of these rock layers and geological events:. When the age of rock is compared to the ages of other rocks or events in geological time.