Biostratigraphy is a branch of geology that uses fossils to date and correlate rock layers. By studying the distribution of different fossilized plants and animals, scientists can determine the relative ages of rocks and understand the history of life on Earth. This method helps geologists identify specific time periods and environmental conditions when certain organisms thrived. In biostratigraphy, the presence of certain fossils, known as index fossils, is particularly important. These fossils are widespread, easily recognizable, and existed for a relatively short time, making them useful for dating rock layers. By comparing these fossils across different locations, researchers can piece together the geological history of an area.