A 35-million-year-old crater under Chesapeake Bay is offering new insights into possible locations for life on Mars. But it also has the potential to threaten the area's groundwater supplies with contamination, according to a new study.
The pit, discovered about 15 years ago, is considered one of the best-preserved examples of the roughly 200 known impact structures on Earth. (See a map of the area.)
The full crater has a diameter of about 56 miles (90 kilometers). That's an oddly large size for a crater believed formed by a comet or asteroid only about 1.3 miles (2 kilometers) wide, said study co-author Gregory Gohn of the U.S. Geological Survey.
At the time, the eastern shore of the U.S. lay near where Richmond, Virginia, sits today, so the object struck a 650-foot-deep (200-meter-deep) sea, he added.
The projectile vaporized upon impact, releasing intense heat for more than 100 miles (161 kilometers), Gohn said.
The collision blew open a crater that was initially about 12.4 miles (20 kilometers) wide and 4.3 miles (7 kilometers) deep.
But the crater walls were not strong enough to support the massive pit and collapsed further, creating a larger pit and allowing salty seawater and broken rock to became trapped in a subsurface cavity.
The crumbling rock stirred up raw materials that allowed life to bloom inside the crater after the waters finally cooled, hinting that life on Mars may also have flourished because of impacts.
(Related: "Any Possible Mars Water or Life Is Deep Below Surface" [May 15, 2008].)
Now, however, the salt water lies dangerously close to freshwater aquifers that supply the local population, the new study found.
Salty Contamination
In 2007 an international team of researchers began drilling about 6 miles (9 kilometers) from the crater's center. Using diamond-containing steel drill bits, the scientists were able to capture rock samples up to a mile (1.8 kilometers) into the impact structure.
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