Meteorite contains 7-billion-year-old stardust, the oldest material on Earth

Scanning electron microscope image of the 6.2-billion-year-old grain of silicon carbide from the Murchison meteorite. Image credit Heck et al doi 10.1073/pnas.1904573117

The Murchison Meteorite on display in Melbourne Museum's Dynamic Earth Gallery.

"We have some grains which are a billion years older than the Sun, making them 5.5 billion years old ... a few grains that are 2 billion years older and we have one grain that is 3 billion years older [than the Sun]". Unlike most of the other stardust that went into building our solar system, these microscopic grains have remained intact since they were shed by aging stars billions of years ago. Proceedings of the National Academy of Sciences.

"They're solid samples of stars, real stardust".

"These are the oldest solid materials ever found, and they tell us about how stars formed in our Galaxy", said Dr. Philipp Heck, a curator at the Field Museum of Natural History and a researcher in the Chicago Center for Cosmochemistry and the Department of the Geophysical Sciences at the University of Chicago.

A pair of grains from the Murchison meteorite.

The paste of ground-up meteorite released a stench "like rotten peanut butter", study co-author Jennika Greer, a graduate student at the Field Museum and the University of Chicago, said in a statement.

The researchers detected the tiny grains inside the meteorite by crushing fragments of the rock and then segregating the component parts in a paste they described as smelling like rotten peanut butter.

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

Once the presolar grains were isolated, the team figured out from what types of stars they came and how old they were. When he visited the town of Murchison in 2019 for the 50th anniversary of the meteorite's landing, he spoke with people who had witnessed the event or collected fragments of the space rock. So the longer a sample is exposed, the more secondary elements are formed. This allows researchers to date it.

"I compare this with putting out a bucket in a rainstorm. Assuming the rainfall is constant, the volume of water that accumulates within the bucket tells you how prolonged it modified into as soon as uncovered", acknowledged Dr Heck.

Presolar grains are more abundant in what we would call these primitive meteorites, Professor Bland said. This in flip informs them how dilapidated it is some distance.

But the age of the presolar grains wasn't the end of the discovery. The sun is 4.6 billion years old, and Earth is 4.5 billion.

Although researchers first identified the grains in 1987 their age could not be determined.

Nonetheless, the oldest yielded a date of around 7.5 billion years dilapidated.

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

"I am sure there are older pre-solar minerals in Murchison and other meteorites, we just haven't found them yet". For context, the Sun is 4.6 billion years old and Earth is 4.5 billion. According to the researchers, this finding suggests that our galaxy went through a period of intense star formation around that time. These grains were originally separated from Murchison meteorite fragments at the University of Chicago over 30 years ago, but they were preserved so future scientists could study them with modern dating technologies.

"In order to explain our age distribution, where we have many more younger grains that we would otherwise expect, we have to explain this by this dust forming from more stars than normal", he said.

Scientists have also discovered that presolars often float in space, stuck together in large clusters like "granola", something that had not been thought of on this scale before.



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