Scientists, while analyzing a meteorite, discovered the oldest material on Earth. They found dust grains within the space rock – which fell to Earth in the 1960s – that are as much as 7.5 billion years old.
An international team of researchers, led by astronomer Philipp Heck of the University of Chicago and the Field Museum, believes that the minuscule dust grains may be leftovers from a stellar explosion billions of years ago. As the dust flew through space, it got scooped up by passing meteorites and comets. The team of researchers described in the journal proceedings of the National Academy of Sciences that the oldest of the dust grains were formed in stars that roared to life long before our solar system was born.
“They’re solid samples of stars, real stardust,” told lead author Philipp Heck, a curator at Chicago’s Field Museum and associate professor at the University of Chicago, to BBC news.
The meteorite in which the grains were found is one of the most well-studied meteorites on Earth. The 220-pound Murchison meteorite plummeted to Victoria, Australia on September 28, 1969. (There were witnesses too- a rare treat for studied meteorites.) It is a type of meteorite called a carbonaceous chondrite and it is one of the most primitive meteorite known to science.
“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 while giving an interview to BBC. “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 in acid, leaving only the stardust. “It’s like burning down the haystack to find the needle,” said Philipp Heck.
To find out how old the grains were, the researchers measured how long they had been exposed to cosmic rays in space. Some of these rays interacted with the matter they encountered and formed new elements. The longer they were exposed, the more of these elements formed. The researchers used a particular form (isotope) of the element neon – Ne-21 – to date the grains.
“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,” said Dr Heck to BBC.
Measuring how many of the new elements are present tells scientists how long the grain was exposed to cosmic rays. Some of the pre-solar grains turned out to be the oldest ever discovered.
Earth formed alongside the rest of the solar system roughly 4.6 billion years ago. The oldest rocks we’ve found to date are about 4.03 billion years old, but the oldest earth minerals ever discovered were actually found in ‘lunar samples’ and date to about 4.1 billion years. However, the oldest yielded a date of around 7.5 billion years old.
The researchers also learned that pre-solar grains often float through space stuck together in large clusters, like granola.
“No one thought this was possible at that scale,” Philipp Heck explained to the BBC news.
This new discovery will help scientists better understand patterns of star growth in the solar system, claimed ‘Popular Mechanics’ in a news report. Heck suspects there are probably other grains just like this one, just waiting to be discovered.