GENERAL GEOLOGY

Detailed explanation-1: -Index fossils are fossils of organisms that lived during only one short period of time. A layer rock with an index fossil in it is close in age to another layer of rock with the same type of index fossil in it. Even though rock layers are of different regions, index fossils indicates that the layers are close in age.

Detailed explanation-2: -Index fossils are useful because they tell the relative ages of the rock layers in which they occur. Geologists use particular types of organisms, such as trilobites, as index fossils.

Detailed explanation-3: -Index fossils can be used to correlate the relative ages of rocks that are separated by vast distances. The cool thing is that we can even correlate rocks from different continents! For example, scientists found Barosaurus fossils inside a layer of Tendaguru rocks in East Africa.

Detailed explanation-4: -Index fossils are commonly used to match rock layers in different places (Figure below). If two rock layers have the same index fossils, then they’re probably about the same age. Using Index Fossils to Match Rock Layers. Rock layers with the same index fossils must have formed at about the same time.

Detailed explanation-5: -Geologists use the law of superposition and law of original horizontality to determine the relative ages of sedimentary rock layers. According to the law of superposition, in horizontal sedimentary rock layers the oldest is at the bottom. Each higher layer is younger than the layer below it.