GENERAL GEOLOGY

Detailed explanation-1: -index fossil, any animal or plant preserved in the rock record of the Earth that is characteristic of a particular span of geologic time or environment. A useful index fossil must be distinctive or easily recognizable, abundant, and have a wide geographic distribution and a short range through time.

Detailed explanation-2: -The fossils that are very distinct at certain times of Earth’s history are called index fossils. Index fossils are commonly used to match rock layers. You can see how this works in Figure below. If two rock layers have the same index fossils, then they’re probably about the same age.

Detailed explanation-3: -Fossils found in a particular rock layer help scientists determine the age of the rock. Scientists use a technique called radiocarbon dating to find out the age of the fossils. Once they know the age of the fossil in the rock, they also know that rock itself is about the same age!

Detailed explanation-4: -Bryozoans are often used as index fossils because they are abundant in many types of sedimentary rocks and are useful for determining the ages of marine and freshwater rocks.

Detailed explanation-5: -It is based on the Law of Superposition which states that in undisturbed rock sequences the bottom layers are older than the top layers.