Answer: Fossils are like biological documents. They prove the existence of species that are now extinct (like dinosaurs). They also show how different organisms that once lived on Earth lived, survived, and acted during different periods of the Earth's ancient, and even more recent history. Fossils can also help scientists and biologists reconstruct the evolutionary histories of present-day species.
Explanation: I hope this helps! Here's a picture of a species' fossils showing the species evolving over millions of years. ( I think it's a horse)