 Fossils can be used to recognize rock layers of "the same or different geologic ages", thereby coordinating locally occurring geologic stages to the overall geologic timeline.The pictures of the fossils of monocellular algae in this USGS figure were taken with a scanning electron microscope and have been magnified 250 times.In the U.S. state of South Carolina three marker species of fossil algae are found in a core of rock whereas in Virginia only two of the three species are found in the Eocene Series of rock layers spanning three stages and the geologic ages from 37.2–55.8 MA.