The teensy tiny microscopic grains of dust were forged in a distant star somewhere between 5 and 7 billion years ago, according to new research. By comparison, our Sun is just 4.6 billion years old.
Eventually, these grains were carried to Earth in a meteorite.
"This is one of the most exciting studies I've worked on," said cosmochemist Philipp Heck of the Field Museum of Natural History and the University of Chicago.
"These are the oldest solid materials ever found, and they tell us about how stars formed in our galaxy."
While it's actually not unheard of for meteorites to contain grains of material that predate the Solar System - they're called "presolar grains" - they are rare, and difficult to identify because the bits of material are so small, and deeply embedded in the rock.
One meteorite that is known to contain presolar grains is the Murchison meteorite, a large, over 100 kilogram (220 pound) chunk of space rock that exploded in the sky over Murchison, Australia in September 1969, scattering its fragments all over the place.
The Field Museum acquired 52 kilograms of the Murchison meteorite, and has spent a great deal of time studying it. A large number of microscopic grains of a mineral called silicon carbide from inside the meteorite were identified as interstellar - and therefore presolar - by 1990, but a precise age has been harder to pin down.
A bunch of these silicon carbide grains had already been isolated from the meteorite back in the 1990s, by grinding down the meteorite to powder and dissolving the unwanted silicate with acid. Back then, the tools scientists used to analyse these grains weren't as advanced as they are now, so Heck and his team decided to submit the grains to the full gamut of tests.
They used scanning electron microscopy, secondary ion mass spectrometry and noble gas mass spectrometry, looking for the effects of exposure to cosmic radiation, which can penetrate solid material such as meteorites and leave its mark on the silicon carbide grains.
"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 explained.
"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."
Forty silicon carbide presolar grains were checked for traces of the particular elements in question - helium-3 and neon-21; these revealed the ages of the grains. A few were quite old, more than 5.5 billion years old, but most of them were younger, between 4.6 and 4.9 billion years old.
A bunch of these silicon carbide grains had already been isolated from the meteorite back in the 1990s, by grinding down the meteorite to powder and dissolving the unwanted silicate with acid. Back then, the tools scientists used to analyse these grains weren't as advanced as they are now, so Heck and his team decided to submit the grains to the full gamut of tests.
They used scanning electron microscopy, secondary ion mass spectrometry and noble gas mass spectrometry, looking for the effects of exposure to cosmic radiation, which can penetrate solid material such as meteorites and leave its mark on the silicon carbide grains.
"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 explained.