Evidence of Oldest-Known Meteorite Impact Discovered in Australia.

Comets and asteroids have been using Earth for target practice for as long as it's existed, but finding evidence of impacts early in the planet's history is surprisingly difficult. An international team of scientists reports finding evidence of what may be the most ancient impact even yet, dating to 3.48 billion years ago. However, they didn't find an impact crater—the researchers made this determination using a smattering of pinhead-size beads of melted rock.

The team discovered evidence of the ancient impact in the volcanic and sedimentary rocks of Australia's Dresser Formation. In 2019, the group spotted structures called spherules in rock cores. These small bead-like structures are left over from impact ejecta—material that is melted and blasted skyward in a split second at the time of impact. The spherules rain down on the surrounding terrain, leaving evidence of the impact long after erosion has wiped the crater from existence. The announcement came at the 54th Lunar and Planetary Science Conference but has not yet been published in a peer-reviewed journal.

After discovering the tiny formations, the team analyzed the rocks for a meteorite signature. They found the spherules contained iridium in high concentrations, nickel-chromium minerals, and rare osmium isotopes—all associated with meteorites. They note that the spherules have the characteristic dumbbell and teardrop shapes of impact ejecta. The researchers conducted radioisotope dating to confirm the spherules were truly ancient and came up with an approximate age of 3.48 billion years.

Source: www.extremetech.com

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