Seven Billion-year-old Stardust Trapped in a Meteorite Is Oldest Material Ever Found on Earth

The oldest material ever found on Earth has been identified, with scientists finding seven billion-year-old grains inside a meteorite that crashed in Australia 50 years ago. The "presolar grains" came from dying stars, with the stardust flung out into interstellar space ready to be used again to form new stars.

Researchers from the University of Chicago first found these grains in 1987. They found the composition to be different to anything else ever found in the solar system. There was also no known process within our solar system that could have led to their formation.

Now, a team of scientists led by Philipp Heck, from the Field Museum of Natural History, Chicago, has worked out how old the stardust is—with some of the grains dating back seven billion years.

"We already knew that they were older than the solar system, hence older than 4.6 billion years," Heck told Newsweek. He explained there were problems when researchers had initially tried to age the dust and that his team has been working on the samples for over 10 years. Over this time, their dating technique has "dramatically improved."

"In particular we now use cosmic ray data from the Voyager 2 spacecraft. Voyager 2 measured the cosmic-ray flux outside of the solar system, the same flux that the grains were exposed to," he said.

Cosmic rays are high energy particles that whizz around space at almost the speed of light, penetrating objects they encounter. The more cosmic rays an object has absorbed, the longer it has been exposed. This makes them a useful method of dating. After isolating the presolar grains, Heck and colleagues found most of them dated to between 4.6 and 4.9 billion years. Some were also found to be older than 5.5 billion years old. Findings are published in PNAS.

"The stars of the majority of the grains were two to 2.5 billion years old when they produced the dust," Heck said. The team believes most of the grains studied were produced during a period of heightened star formation. At this time older stars were dying and new ones were forming.

Image depicting a presolar grain found in a meteorite. The grains came from dying stars and date back seven billion years. ESA/Hubble and NASA. Inset courtesy of Janaína N. Ávila

The presolar grains discovered got trapped in a forming object in our solar system about 4.6 billion years ago.

The stars the dust came from were about 1.6 to 1.9 times as massive as the sun and are known as low-to intermediate mass asymptotic giant branch stars, Heck said. "The enhanced star formation episode was centered around seven billion years ago," he explained. "It has died down long before the sun formed 4.6 billion years ago. The sun formed from the products of those stars. These stars that formed seven billion years ago were actually the parent stars of our sun."

Heck said the meteorite studied may contain grains even older than seven billion years, they just have not been found yet. They are now separating more grains from the meteorite, as well as looking at other meteorites to find more ages.

Studying these particles, he said, is important as they are the only solid samples of stars they have. This means they can be studied for composition. "The study of these particles is an independent way of studying our galaxy, in addition to the completely different way of studying the galaxy, by astronomical observations and models. It can be considered ground truth for remote sensing methods," Heck said.

"We hope future work will enable us to dive even deeper in time to uncover past events that occurred in our galaxy."