Learning the most from the least
Not all fossils are large bones of things like dinosaurs or mammoths. Some of them are small enough to require a microscope in order to identify them. Called microfossils, these tiny fragments, and even remains of single-celled organisms, can tell us a good deal about things like the climate, the vegetation, the temperature, and chemical composition of the water and air when a given layer or strata of rock was laid down.
Here’s a link to an article about using microfossils to solve the mystery of what killed the last of the mammoths.
Here’s an article that talks about the use of microfossils for finding oil deposits.
And here are some articles about a few different types of microfossils.