Meteorite grains older than solar system + Giant meteorite struck 800k yrs ago

Almost 800,000 years Ago, an enormous meteorite struck Earth. Now we know where.

EXCERPT: 20% of the surface of Earth’s Eastern Hemisphere is littered with a certain kind of rock. Black, glossy blobs called tektites are spread throughout Australasia. Scientists know they’re from a meteorite strike, but they’ve never been able to locate the crater where it struck Earth. Now a team of scientists seems to have found it. The chunk of rock that crashed into Earth about 790,000 years ago, during the Early Pleosticine. It was about 2 km (1.2 miles) wide. Its impact on Earth was enormously powerful, spreading debris across Asia, Australia, and even Antarctica.

[...] In the new paper, a team of researchers say they have four separate lines of evidence showing that the impact crater lies under the Bolaven Plateau volcanic field. The paper is titled “Australasian impact crater buried under the Bolaven volcanic field, Southern Laos.” The paper is published in Proceedings of the National Academy of Sciences of the United States of America.

[...] The team also measured the age of the rocks in the volcanic plateau to see if there was a fit. If the crater is buried under the lava, then the lava must be younger than the tektites. The scientists point out in their paper the appearance of the volcanic plateau. They say that most of the land-forms appear youthful, and radioisotopic dating supports that.

[...] This impact is young enough to have influenced humans. Evidence of human activity is intermingled with the Australasian strewnfield. In Guangxi, Southern China, archaeological artifacts including hand axes were found among the tektites, indicating that a population of Homo Erectus was living in the area during and after the impact. There’s also significant charcoal in the area, and scientists think that the impact started vast fires. One possibility is that the early humans moved into the area after the impact and fires, making tools out of the newly-exposed rock. (MORE - details)

Stuff older than solar system found inside meteorite that hit Australia

EXCERPT: A meteorite that crashed into rural southeastern Australia in a fireball in 1969 contained the oldest material ever found on Earth, stardust that predated the formation of our solar system by billions of years, scientists said on Monday. A scanning electron micrograph of a presolar silicon carbide grain, about 8 micrometers in its longest dimension, from a meteorite that crashed into Australia in 1969 is seen in this image released in Chicago, Illinois, U.S. January 13, 2020. Janaina N. Avila/Handout via REUTERS

The oldest of 40 tiny dust grains trapped inside the meteorite fragments retrieved around the town of Murchison in Victoria state dated from about 7 billion years ago, about 2.5 billion years before the sun, Earth and rest of our solar system formed, the researchers said. In fact, all of the dust specks analyzed in the research came from before the solar system’s formation - thus known as “presolar grains” - with 60% of them between 4.6 and 4.9 billion years old and the oldest 10% dating to more than 5.6 billion years ago.

The stardust represented time capsules dating to before the solar system. The age distribution of the dust - many of the grains were concentrated at particular time intervals - provided clues about the rate of star formation in the Milky Way galaxy, the researchers said, hinting at bursts of stellar births rather than a constant rate.

“I find this extremely exciting,” said Philipp Heck, an associate curator at the Field Museum in Chicago who led the research published in the scientific journal Proceedings of the National Academy of Sciences. “Despite having worked on the Murchison meteorite and presolar grains for almost 20 years, I still am fascinated that we can study the history of our galaxy with a rock,” Heck added. (MORE - details)

[...] The grains initially formed in interstellar space out of material ejected from mature stars that then condensed into dust. The researchers who identified the grains think many of them likely were created following a boom in star formation the Milky Way experienced some 7 billion years ago. If confirmed, the new finding demonstrates that researchers can study meteorites to better understand the history of star formation in our galaxy.

When small to medium stars (from about 0.5 to 5 times the mass of the sun) approach the ends of their lives, they expand into red giant stars and blow off their outer layers. This results in beautiful, expanding clouds of material that astronomers call planetary nebulae. Over time, the material in these planetary nebulae cools and condenses into grains of dust and minerals. Some of these grains are then incorporated into clumps of interstellar gas, helping form new generations of stars, planets, asteroids and so on.

Any presolar grains that were present when Earth first formed are now long gone, changed by our planet’s geologic processes — including in volcanoes and through plate tectonics. But meteorites that fall to Earth from space rocks preserve these cosmic time capsules. Ever since researchers began finding presolar grains in meteorites in 1987, they've studied these ancient relics to find out how old they are and where they came from. (MORE - details)

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