In a new analysis of an old meteorite, scientists were able to identify the oldest material that’s ever been found on Earth. They discovered stardust that’s been dated back to 7 billion years ago.
On September 28, 1969, near Murchison, Victoria, Australia, a huge 220 pound (100 kilograms) meteorite struck the Earth. Scientists discovered that the meteorite contained interstellar dust that was made from presolar grains (dust grains that are much older than our sun) created by dying stars. In fact, the presolar grains ranged in age from around 4 million years older than our sun to 3 billion years older. Our sun was created 4.6 billion years ago.
Philipp Heck, who is the Robert A. Pritzker Associate Curator of Meteoritics and Polar Studies at the Field Museum of Natural History in Chicago, as well as the lead author of the study (which can be read in full here), said that this is the first time ever that presolar grains have been found on Earth and it’s because volcanism and plate tectonics as well as other Earthly processes heated up and modified any presolar dust that would have already been here during the early stages of when our planet was forming.
He told Live Science that the large asteroid that produced the Murchison meteorite is “an almost-inert piece of rock that formed from the solar nebula and hasn't changed since then.” While the majority of presolar grains are approximately 1 micron in length, the ones that were found on the Murchison meteorite were between 2 and 30 microns in length. “We call them ‘boulders’,” Heck stated, adding, “We can see them with an optical microscope.”
In their study, Heck and his colleagues looked at 40 “boulders” by grinding up parts of the meteorite and added acid which caused minerals and silicates to dissolve, leaving the presolar grains which are resistant to acid. The team then measured how much cosmic rays were exposed to the grains while they were in space for billions of years in order to find out how old they were. They found that around 60% of the grains date back to between 4.6 billion and 4.9 billion years ago and could have been the result of a “little baby boom” from stars being born approximately 7 billion years ago in our galaxy. In fact, many astronomers have found evidence supporting a large spike in star formations around 7 billion years ago.
“And then it took about two to two-and-a-half billion years for those stars to become dust producing,” Heck said, adding, “When a star forms, it doesn't produce dust. During most of its life, the star doesn't produce dust. The stars only produce dust at the end of their lives.”