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August 20, 2019 10:00 am

35 Million-Year-Old Asteroid Left a Trail of Destruction Across the Eastern US

schwit1 shares a report from Space.com: About 35 million years ago, an asteroid traveling nearly 144,000 mph (231,000 km/h) smashed into the Atlantic Ocean near the modern-day town of Cape Charles, Virginia. The space rock vaporized instantly, but its impact triggered a gargantuan tsunami, cast up a monsoon of shattered rocks and molten glass that spanned hundreds of miles and carved out the single largest crater in the United States -- the so-called Chesapeake Bay impact structure. Today, that 25-mile-wide (40 kilometers) crater is buried half a mile below the rocky basement of Chesapeake Bay -- the 200-mile-long (320 km) estuary linking Virginia and Maryland on the East Coast. That hasn't stopped scientists from trying to piece together the site's mysterious history since it was first discovered during a drilling project in 1990. In a recent study of ocean sediment cores taken almost 250 miles (400 km) northeast of the impact site, researchers found traces of radioactive debris dating to the time of the strike, providing fresh evidence of the impact's age and destructive power. In their recent study (published in the journal Meteoritics and Planetary Science), researchers from Arizona State University dated 21 microscopic shards of zircon -- a durable gemstone that can survive underground for billions of years. These zircons were lodged in a sediment core taken from roughly 2,150 feet (655 meters) below the Atlantic Ocean. Not only is zircon commonly found in tektites, but it is also a choice mineral for radiometric dating, thanks to some of its radioactive elemental components. In this case, the researchers used a dating technique called uranium-thorium-helium dating, which looks at how radioactive isotopes, or versions, of uranium and thorium decay into helium. The team found that the 21 crystals ranged widely in age, running the gamut from about 33 million to 300 million years old. The two youngest samples, which had an average age of about 35 million years old, fit in with previous studies' estimates for the time of the Chesapeake Bay impact.

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