Oldest material on Earth: Scientists discover 7.5 billion-year-old stardust
The Murchison meteorite, which impacted Australia decades ago, contains astral dust that predates the birth of the Sun.
Scientists have discovered the oldest material on Earth – Stardust which is as 7.5 billion years old, trapped inside a huge, rocky meteorite that hit our planet half a century ago.
Our Sun is around 4.6 billion years old, meaning this stardust existed long before our Sun or Solar System were even a reality. This ancient interstellar dust, made of presolar grains (dust grains that predate our Sun), was belched into the Universe by dying stars during the final stages of their lives.
Researchers have described the result in “Proceedings of the National Academy of Sciences” journal.
Stars are born when gas, dust and heat combine in just the right way. They can exist for millions or even billions of years before dying and expelling their key ingredients into space. This in turn helps new stars to be born, creating a space daisy chain, according to a CNN report.
On the other hand, meteorites, if they don't slam into too many things, can act like time capsules of the materials trapped within them, like stardust. That's why the discovery of the presolar grains is such a rarity -- only 5 per cent of meteorites found on Earth contain them. Their impossibly tiny size is difficult to fathom.
"They're solid samples of stars, real stardust," said lead author Philipp Heck, a curator at Chicago's Field Museum and associate professor at the University of Chicago.
A team of researchers from the US and Switzerland analysed 40 pre-solar grains contained in a portion of the Murchison meteorite, that fell in Australia in 1969.
"It starts with crushing fragments of the meteorite down into a powder," said co-author Jennika Greer, from the Field Museum and the University of Chicago.
"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 whiffy paste was then dissolved in acid, leaving only the stardust.
To work out how old the grains were, the researchers measured how long they had been exposed to cosmic rays in space. These rays are high-energy particles that travel through our galaxy and penetrate solid matter.
Some of these rays interact with the matter they encounter and form new elements. The longer they are exposed, the more of these elements form. The researchers used a particular form (isotope) of the element neon - Ne-21 - to date the grains.
Measuring how many of the new elements are present tells scientists how long the grain was exposed to cosmic rays. This in turn informs them how old it is.
Some of the pre-solar grains turned out to be the oldest ever discovered.
Based on how many cosmic rays had interacted with the grains, most had to be 4.6-4.9 billion years old. For comparison, the Sun is 4.6 billion years old and the Earth is 4.5 billion.
However, the oldest yielded a date of around 7.5 billion years old.
"Only 10% of the grains are older than 5.5 billion years, 60% of the grains are ‘young’ (at) 4.6 to 4.9 billion years old, and the rest are in between the oldest and youngest ones,” Dr Heck told the BBC.
Previously, the oldest pre-solar grain dated with neon isotopes was around 5.5 billion years old.