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In the warm late Eocene, sea levels were high, and tidewater Virginia lay in the coastal shallows. The shore of eastern North America, about where Richmond, Virginia, is today, was covered with dense tropical rainforest, and the waters of the gently sloping continental shelfThe continental shelf is an area of relatively shallow sea water that is found on the edge of each continent. The shelf typically ends at a very steep slope (called the shelf break . The sea bottom below the break is the continental slope which has a much were rich with marine life that was depositing dense layers of limeProperties General Name Calcium carbonate Chemical formula Ca CO Appearance White solid Physical Formula weight 100. 1 amu Melting point Liquifies under high pressure at 1612 K (1339 °C) Boiling point decomposes at 1172 K (899 °C) Density 2. 7 ×103 kg/ m3 from their microscopic shellAmongst other things, a shell is: An animal shell, the hard, rigid outer covering of an animal such as a mollusk or gastropod or tortoise or turtle. See also: shell (material). The hard outer layer of eggs. The hard outer layer of some plant fruiting bodis.
Suddenly, many times faster than a bullet, the bolide flashed across the sky and hit. Whether it was an icy cometHalley's Comet nucleus sunlit from the left. A comet is a relatively small astronomical object similar to an asteroid but composed largely of ice. In Earth's solar system, the orbits of comets may extend past that of Pluto; of the comets which enter the i or a small asteroidAn asteroid is a small, solid object in our Solar System, orbiting the Sun. An asteroid is an example of a minor planet (or planetoid , which are much smaller than planets. The asteroids are believed to be remnants of the protoplanetary disc which were no, it punched a deep hole through the sediments and into the graniteGranite is a common and widely-occurring group of intrusive felsic igneous rocks that form at great depths and pressures under continents. Granite consists of orthoclase and plagioclase feldspars, quartz, hornblende, biotite, muscovite and minor accessory continental basement rock , fracturing it to depths of 8 kilometers, and raised a 'peak ring' around it. The deep crater, 38 km across, is surrounded by a flat-floored terrace-like ring trough with an outer edge of collapsed blocks forming ring faults. The entire circular crater is about 85 km in diameter and 1.3 km deep, an area twice the size of Rhode Island, and nearly as deep as the Grand Canyon.
The surrounding region was engulfed in widespread devastation. USGS scientist David Powars, one of the impact crater's discoverers, has described the immediate aftermath: "Within minutes, millions of tons of water, sediment, and shattered rock were cast high into the atmosphere for hundreds of miles along the East Coast." An enormous seismic tsunami engulfed the land and possibly even overtopped the Blue Ridge Mountains. The sedimentary walls of the crater progressively slumped in, widened the crater, and formed a layer of huge blocks on the floor of the ring-like trough. The slump blocks were then covered with the rubble or ' breccia'. The entire bolide event, from initial impact to the termination of breccia deposition lasted only a few hours or days. In the perspective of geological time, the 1.2 km-thick breccia is an instantaneous deposit. The crater was then buried by additional sedimentary beds, which have accumulated during the ensuing 35 million years.
Until 1983, no one suspected the existence of such a crater buried 300-500 meters beneath the lower part of Chesapeake Bay and its surrounding peninsulas. The first hint was a 20 centimeter-thick layer of ejecta that turned up in a drilling core taken off Atlantic City, New Jersey, far to the north. The layer contained the fused glass beads called tektites and shocked quartz grains that are unmistakable signs of a bolide impact.
In 1993 oil exploration revealed the extent of the crater.
The continual slumping of the rubble within the crater, has affected the flow of the rivers and shaped Chesapeake Bay. The impact crater created a long-lasting topographic_depression, which helped predetermine the course of local rivers and the eventual location of Chesapeake Bay. Most important for present-day inhabitants of the area, the impact disrupted aquifers. The present freshwater aquifers lie above a deep salty brine, making the entire lower Chesapeake Bay area susceptible to groundwater contamination.