Below, we will discuss some major types of fossils and why they are relevant to relative dating.

Index fossils are those that are used to define geologic time.

The law of lateral continuity states that the deposition of sediment is continuous unless there is a barrier or subsequent changes in the landscape break up layers.

Absolute dating can be helpful when there is some uncertainty about whether all features of the rock are present.

Inclusions occur where a sedimentary rock forms around a foreign object.

They occur where layers of rock were either eroded away or never deposited and cemented in the first place.

Sometimes there is evidence that an unconformity has occurred; other times, there is no way of knowing if there is a break in the relative time scale.

Relative dating is an important topic in AP Environmental Science.

It is used to help identify what ancient environments looked like, when certain kinds of animals lived, and what changes have happened in a given environment over many years.Index fossils can also be used to determine relative ages of nearby layers of sedimentary rocks.Characteristic fossils belong to a period, but do not define the time period.Smaller marine organisms are also limited in geologic time because they are often sensitive to environmental changes making them a boom-and-bust kind of organism.That is, they become abundant, and then their sensitivity to environmental changes causes them to become extinct.Effective index fossils have several characteristics—they are widespread, distinctive, abundant, and limited in geologic time.