Oldest material on Earth discovered in meteorite

  • Oldest material on Earth discovered in meteorite

Oldest material on Earth discovered in meteorite

This discovery supports findings by other astronomers that indicate a dramatic spike in star formation around 7 billion years ago, the researchers reported.

The researchers reckon parts of the grains started off in a star that formed seven billion years ago, during a time when part of the Milky Way was experiencing higher levels of star formation than today. "Some people think that the star formation rate of the galaxy is constant", Heck said.

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In 1969, a fireball was seen exploding in the sky near Murchison, Victoria, Australia.

But the age of the presolar grains wasn't the end of the discovery.

For a new study published in the journal Proceedings of the National Academy of Sciences, scientists analyzed presolar grains from one of these meteorite fragments.

The oldest solid material on Earth has just been identified, and it predates the Solar System itself by at least a few hundred million years.

When large, orphan space rocks form - such as the asteroid that produced Murchison - they, too, can pick up ancient, interstellar dust.

Lead author Philipp Heck, a curator at the Field Museum and associate professor at the University of Chicago, said: "This is one of the most exciting studies I've worked on".

Scanning electron microscope image of the 6.2-billion-year-old grain of silicon carbide from the Murchison meteorite. Dust grains floating through space get bombarded by high-energy particles called cosmic rays. Since presolar grains are formed when a star dies, they can tell us about the history of stars. "These bits of stardust became trapped in meteorites where they remained unchanged for billions of years, making them time capsules of the time before the Solar System", Dr.

"Each grain probably came from a different star", Dr Heck said. This grain is about 8 micrometers in size. The age distribution of the dust - numerous 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. Those cosmic rays react with rock to form new elements that accumulate over time.

Measuring how numerous new elements are present tells scientists how long the grain was exposed to cosmic rays.

Some of the grains were older than our sun, which is 4.6 billion years old, and our planet, which is 4.5 billion years old. Our sun, by comparison, is 4.6 billion years old, and Earth is 4.5 billion years old. "With stardust, we can trace that material back to the time before the Sun".

The researchers learned that some of the presolar grains in their sample were the oldest ever discovered on Earth. Billions of years later, a chunk of that asteroid crashed into Australia.

Previous studies have noted that similar presolar grains have ages ranging from 5 billion to 4.6 billion years old, but the upper age limit of this Murchison stardust takes the the cake.

That makes these presolar grains useful pieces of evidence in the study of our galactic history.

Meteorites containing stardust are incredibly rare.

"We have more young grains that we expected", Heck said.

"Only a few meteorites are as large as Murchison and as rich in grains as Murchison", he said.

A team of researchers from the United States and Switzerland analysed 40 pre-solar grains contained in a portion of the Murchison meteorite, that fell in Australia in 1969. Inset: SiC grain with ~8 micrometers in its longest dimension.

"It starts with crushing fragments of the meteorite down into a powder", Jennika Greer, a co-author of the study, said in a press release.

"We use a chemical recipe of different chemical reagents, mainly acids, to dissolve away everything else, and then we extract those minerals".

Since the majority of the 40 grains Heck's team studied were around the same age, his team hypothesized that most came from stars that formed in one big burst. This in turn acts as a food, helping to create new stars. The new study is evidence of the latter.

As for the oldest grain, Haenecour says, "I think it is hard to really actually know that this grain is 7 billion years old", but adds that it does appear to be much older than the other grains in the study.