Meteorite Grains Are the Oldest Known Solid Material on Earth

Eloise Marshall
January 14, 2020

The oldest of 40 small grains of dust trapped inside the meteorite Fragments recovered around the city of Murchison in the state of Victoria date back about seven billion years ago, about 2.5 billion years before the sun, Earth and the rest of our solar system formed, the researchers said.

That's because plate tectonics, volcanism and other planetary processes heated and transformed all the presolar dust that may have collected during Earth's formation, said lead study author Philipp Heck, the Robert A. Pritzker Associate Curator of Meteoritics and Polar Studies at the Field Museum of Natural History in Chicago.

These presolar particles were forged before the Sun was formed in environments with completely different chemical compositions.

When stars die after millions or billions of years, their particles end up in outer space - eventually forming new stars as well as moons or meteorites.

Heck said the meteorite studied may contain grains even older than seven billion years, they just have not been found yet.

In the future, Heck and others will isolate more presolar grains from meteorites such as Murchison and continue to date them using the cosmic ray technique.

The materials examined in the study published in the Proceedings of the National Academy of Sciences are called pre-solar mineral grains formed before the birth of the Sun.

"It begins with crushing fragments of the meteorite down correct into a powder", acknowledged co-writer Jennika Greer, from the Self-discipline Museum and the College of Chicago.

This whiffy paste was then dissolved in acid, leaving only the stardust.

"It's like burning down the haystack to find the needle", Heck said in the release.

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Once the presolar grains were isolated, the researchers figured out from what types of stars they came and how old they were by measuring their exposure to cosmic rays.

"Some of these cosmic rays interact with the matter and form new elements", Heck said. "When these grains flow through space, they're exposed to cosmic rays, [and] the galactic cosmic rays that they are exposed to are predominantly high-energy protons", Heck says.

Scientists previously had found a pre-solar grain in the Murchison meteorite that was about 5.5 billion years old, until now the oldest-known solid material on Earth.

Dr Heck told BBC News: "Ideal 10% of the grains are older than 5.5 billion years, 60% of the grains are "younger" (at) 4.6 to 4.9 billion years dilapidated, and the remaining are in between the oldest and youngest ones".

In 1969, a 4.6-billion-year-old meteorite struck Murchison, Australia.

Stardust got on the chondrite, not our Solar system was formed.

Heck and colleagues also hypothesize that the majority of the grains in the study could have formed during a period of active star formation about 7 billion years ago, which would have produced large amounts of dust roughly 4.6 to 4.9 billion years ago-the same age as most of the grains. "Some people think that the star formation rate of the galaxy is constant", Heck said. "Stardust is the oldest material to reach Earth, and from it, we can learn about our parent stars, the origin of the carbon in our bodies [and] the origin of the oxygen we breathe". "When a star forms, it doesn't produce dust". "With this study, we have directly determined the lifetimes of stardust". Stardust is the remnant material left behind after the death of a star in a supernova.

The tiny granules of stardust, shed by ancient stars as they expired, reveal clues about how stars formed in the Milky Way.

"It's so exciting to look at the history of our galaxy".

The stars the dust came from were about 1.6 to 1.9 times as massive as the sun and are known as low-to intermediate mass asymptotic giant branch stars, Heck said.

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