Cosmochemist Philipp Heck of the Field Museum of Natural History and the University of Chicago has identified the oldest material on Earth. It’s a 5-7 billion-year-old stardust which he found inside a meteorite that struck our planet half a century ago. By comparison, our Solar System is just 4.6 billion years old.
“This is one of the most exciting studies I’ve worked on,” says Heck, who is also a lead author of the paper describing the findings in the Proceedings of the National Academy of Sciences. “These are the oldest solid materials ever found, and they tell us about how stars formed in our galaxy.”
The discovery was made from a 52-kilogram chunk of the Murchison meteorite, the meteorite that exploded in the skies of Australia in September 1969. The stardust, called technically as presolar grains are rare substances in Earth. They are difficult to identify as the material is so small and embedded deep within the larger mass of the space rock.
The fact that Murchison meteorite had presolar particles in them was confirmed back in 1990 itself. As the tools back then limited the analysing capabilities of the scientists, they were never able to deduce the precise age of these particles.
Silicon Carbide grains were already isolated from the meteorite earlier by grinding a piece of the rock and washing it with acid. Heck and his team ran the grains on a plethora of tests again to find new information.
Scanning electron microscopy, secondary ion mass spectrometry and noble gas mass spectrometry were used to look for the effects of exposure to cosmic radiation. These radiations can penetrate solid material and leave its mark on the silicon carbide grains. Heck explains that “Some of these cosmic rays interact with the matter and form new elements. And the longer they get exposed, the more those elements form,”.
Almost miraculously these grains somehow stood the test of time, probably because they are deeply embedded within the rock, to reach Earth and for us to discover. The team tested for traces for helium-3 and neon-21 elements, which helped them reveal the age of the grains.
The grains were identified to be of the age range of 4.6 billion to 5.5 billion years. His team notes with a surprise that the majority of the grains belong to a relatively younger group between 4.6 and 4.9 billion years old.
“Our hypothesis is that the majority of those grains, which are 4.9 to 4.6 billion years old, formed in an episode of enhanced star formation,” Heck said. “There was a time before the start of the Solar System when more stars formed than normal.”
They are estimating the said period of star formation occurred around 7 billion years ago. At an advanced stage, the stars must have sent these grains as outflows similar to our solar flares which then later got taken up by clump of other debris finally forming our Murchison meteorite.
Heck believes his findings will be of use to dispel the notion that star formation is a constant. The age variation of the grains he found is direct evidence for the view that our galaxy, the Milky way had a period of enhanced star formation.