Oldest material on Earth is stardust found in meteorite

The oldest material known to exist on Earth was just discovered by a group of researchers, working on a meteorite that fell fifty years ago in Australia. The space object, which felt on Earth in the 1960s, had dust grains within that were formed 5 to 7 billion years ago, preceding the formation of the solar system.

Some of the pre-solar grains in the Murchison meteorite (inset) could have come from evolved stars similar to the Egg Nebula (pictured). Credit ESA/Hubble/NASA

Stars have life cycles, born when dust and gas floating through space find each other and then collapse in on each other and heat up. They continue to burn for billions of years until they die, setting off a supernova explosion. When that happens, they create particles known as stardust that are expelled into the universe eventually forming new stars.

Researchers from the Field Museum, the University of Chicago, ETH Zurich and other universities found presolar grains in the meteorite, which are minerals formed before the Sun was born. The stardust was trapped in the meteorites and remained unchanged for billions of years.

Presolar grains are usually hard to find as they are only found in about 5% of the meteorites that have fallen to Earth. The Murchinson meteorite, which fell in Australia in 1969, was filled with them. The study, published in the journal Proceedings of the National Academy of Sciences, now took a closer look at them.

“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. “Once all the pieces are segregated, it’s a kind of paste, and it has a pungent characteristic – it smells like rotten peanut butter.”

The researchers worked to determine the age of the grains by measuring how long they had been exposed to cosmic rays in space. The rays are high-energy particles that travel through the galaxy and penetrate solid matter.

Some of the grains in the sample were the oldest ever discovered, the study found. Most of them were 4.6 to 4.9 billion years old, and some were even older than 5.5 billion years, something never seen before. For context, the Sun is 4.6 billion years old, and Earth is 4.5 billion.

Lead author Philipp Heck said: “Only 10% of the grains are older than 5.5 billion years, 60% of the grains are “young” (at) 4.6 to 4.9 billion years old, and the rest are in between the oldest and youngest ones. I am sure there are older pre-solar minerals in Murchison and other meteorites, we just haven’t found them yet.”

The findings revive the debate over whether or not new stars are formed at a steady rate or whether there are highs and lows in the number of new starts over time. Also, thanks to the findings, researchers now know that pre-solar grains float through space together in large clusters.

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