In Depth

What is the oldest material on Earth?

New research reveals that grains in meteorite that hit our planet 50 years ago predate the Solar System

The oldest material known to exist on Earth has been discovered in a rock that crashed into rural southeastern Australia in 1969, scientists have announced.

The researchers say the meteorite contains “pre-solar grains” that date back to up to seven million years before the birth of our solar system, Al Jazeera reports.

“They’re solid samples of stars, real stardust,” says Philipp Heck, the lead author of a paper on the study published in the journal Proceedings of the National Academy of Sciences.

So just what have scientists found?

Five decades ago, a lump of space rock dubbed the Murchison meteorite crashed near the town of the same name in the Australian state of Victoria. In the years since, different teams of researchers have probed the rock in a series of studies to identify its organic compounds and other properties.

About 30 years ago, scientists established that the meteorite contained pre-solar grains - described by science news site New Atlas as “tiny grains of silicon carbide older than the Sun”. 

But the exact age of the material has only now been determined.

This week, scientists revealed that an analysis of 40 of the tiny dust grains show that most are between 4.6 and 4.9 billion years old, while the oldest date back about seven billion years - about 2.5 billion years before the Sun, the Earth and rest of our solar system formed.

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How did they date the stardust?

“It starts with crushing fragments of the meteorite down into a powder,” explains Jennika Greer, a graduate student who works alongside study author Heck at the University of Chicago and the city’s Field Museum. “Once all the pieces are segregated, it’s a kind of paste, and it has a pungent characteristic - it smells like rotten peanut butter.”

This paste was then dissolved with acid until only the pre-solar grains remained. “It’s like burning down the haystack to find the needle,” says Heck.

Once the grains were isolated, the researchers calculated their age by measuring their exposure to cosmic rays - “high-energy particles that fly through our galaxy and penetrate solid matter”, he explains. 

“Some of these cosmic rays interact with the matter and form new elements. And the longer they get exposed, the more those elements form,” Heck continues. “I compare this with putting out a bucket in a rainstorm. Assuming the rainfall is constant, the amount of water that accumulates in the bucket tells you how long it was exposed.”

The team “look forward to all of these discoveries furthering our knowledge of our galaxy”, reports Science Daily.

“With this study, we have directly determined the lifetimes of stardust,” says Heck. “We hope this will be picked up and studied so that people can use this as input for models of the whole galactic life cycle.”

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