Impact craters are widespread throughout the solar system and can be classified as simple (i.e., bowl-shaped - Meteor Crater Arizona) and complex (i.e., terraced walls and central uplifts - Gosses Bluff Australia). When one looks at the other planets, one finds surfaces having countless craters that range in diameter from a few meters to hundreds of kilometers. The Earth too has been bombarded for billions of years by the same asteroids and comets that produced craters on the other planets, but Earth's plate tectonics and active erosional processes have removed most of these scars. There are some 150-200 recognized impact structures on the Earth, ranging in size from a few meters (Henbury Craters in Australia) to ~300 km (Vredefort in South Africa) ranging in age from recent (1947 Sikhote Alin Russia) to Proterozoic (Vredfort South Africa and Sudbury Canada). We have a fairly large impact structure just down the road the Chesapeake Bay Structure, centered at Cape Charles Virginia on the Delmarva Peninsula. The Chesapeake Bay Structure is about 85 km in diameter and some 35.5 million years old. It is composed of a central uplift surrounded by an inner-basin with a raised basement rim in turn surrounded by an annular zone of slump blocks and filled with breccia and overlain by younger sediments of the Atlantic Coastal Plain.
JEFFERY PLESCIA is a research scientist at Johns Hopkins University Applied Physics Laboratory, where he researches terrestrial impact craters, hyperthermophile organisms of Yellowstone National Park, and geologic processes on Mars. He holds a B.S. in Geology from the University of Miami and an M.S. and Ph.D. in Geophysics from the University of Southern California. Previous research has included participating in the Voyager Imaging Science Experiments for Jupiter, Saturn and Uranus, studying Martian volcanism, tectonism and general geology, and surveying large terrestrial craters to determine their structure. He has served on the research and technical staff positions at the Jet Propulsion Laboratory, California Institute of Technology, U.S. Geological Survey, the NASA Solar System Exploration Division, including managing the NASA Planetary Geology and Geophysics Program.
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