Fossils are direct or indirect remains of organisms preserved in media such as sedimentary rock, amber, ice, or tar.

Fossils have been found that indicate organisms existed well over 3 billion years ago.

-These organisms were simple, single-celled organisms.

About a billion years ago, increasingly complex multi-cellular organisms began to evolve.

The higher up you go in an undisturbed rock stratum (rock layer), the younger the rock layers become and therefore it is believed the fossils within these layers, as compared to lower rock layers.

-Relative Dating of Undisturbed Sedimentary Rock and its Fossils Upper strata generally contain fossils of younger, more complex organisms, whereas, the lower strata contain fossils of simpler life forms.

-This means there is a tendency toward increasing complexity in life forms over time.

When comparing fossils in undisturbed strata, fossils can be found in upper strata which, although different from fossils in lower strata, resemble those fossils.

-This suggests links between modern forms and older forms, as well as divergent pathways from common ancestors.