What is an index fossil used for in geology?

An index fossil is a fossil that is particularly useful for dating and correlating the age of rock layers. These fossils are typically from organisms that lived during a specific time frame and were widespread, making them ideal for identifying and dating the geological periods in which they are found. The presence of an index fossil in a rock layer can provide information about the relative age of that layer compared to others, allowing geologists to establish a chronological sequence of events in geologic history.

Index fossils contribute to the understanding of the geologic time scale and can help in correlating rock layers from different locations, providing insights into the environments and conditions of the past. Their unique characteristics help in distinguishing different layers, making them invaluable in the study of stratigraphy and the interpretation of Earth's history.