Paleontology and geology
Ice sheets advanced and retreated across the landscape north of Maryland during the Early Quaternary (Pleistocene), but never covered the state. Pollen from pine and other cool-climate plants in some Pleistocene sediments in eastern Maryland indicate times of lower temperatures as the ice sheets advanced. Sea levels dropped nearly 100 meters during these glacial intervals, and mastodons roamed the newly exposed land. Their teeth have been recovered from sediments deposited in terrestrial rivers and swamps. Fossils of marine clams, oysters, and snails indicate interglacial times of warmer climate, when sea levels rose to cover the eastern part of the state.