A fossil from an organism that existed for a short time, it is used to determine the age of other fossils. Index fossil. An index fossil is a tool scientists use to figure out how old other rocks and fossils are by comparing them.
Imagine trying to remember the year a certain event took place by recalling a specific fashion trend that was popular at the time. Just like how that distinct fashion style can instantly pinpoint the year, an index fossil acts as a marker to determine the age of other fossils found in the same layer. The fashion trend is like the index fossil, existing for a short period but being highly recognizable, allowing us to accurately identify the timeframe of other events (or fossils) surrounding it.
