Question

How do index fossils help determine the age of rock layers?

Answer 1

Hint: Index fossils are used to find different geological periods. Index fossils are any plant or animal preserved in between the rock layers of earth during various geological periods which is the characteristic of that particular geological age or era. Index fossils are useful as they tell the age of the rock layer in which they tend to occur.

Complete answer:
Earth tends to be changing since the beginning of time. There are so many drastic changes occurring on earth during a long period of time. Fossils help us to get to know what kind of changes the earth undergoes earlier.
As the time passes rocks tend to form various layers called Strata. These strata help us determine the ecological periods. Fossils occur for a distinct time period or era. Index fossils help to distinguish between two strata or layers as they occur for a limited period of time. Animals which evolve easily or are distributed over a wide range of areas are considered good index fossils like pigs and rodents.
If a certain type of index fossil is found under a rock layer it can determine the geological period of that rock layer. A rock layer with an index fossil in it is close to the age of another rock layer with the same type of index fossil in it. Even if the rock layers are found to be in different regions the index fossil indicates that they are of the same geological era or time period.
So it can be said that Index fossils are very helpful to determine the age of the rock layer.

Note: The study of various layers or strata is called Stratigraphy. In this it is understood that the various layers are formed under various geological eras. The wall of the Grand Canyon in Arizona USA we can see the various exposed strata or individual rock layers.