The oldest material on Earth was discovered in a meteorite that fell 50 years ago in Australia.
The Murchison meteorite fell in Victoria State in south-eastern Australia back in 1969. The substances that the meteorite contained were made available for scientific research and were also provided to museums around the world. The University of Chicago has been studying presolar grains-minerals from the meteorite for about 30 years.
Presolar grains-minerals were formed before the creation of our Sun and they are practically stardust (particle debris from a supernova explosion). Those particles may be trapped inside new stars, planets, moons or meteorites and remain unchanged for billions of years, providing insight about the Universe so long ago. However, finding those particles is extremely challenging as they are contained in just 5% of the meteorites that have fallen on Earth. Murchison meteorite is considered a valuable discovery that contains significant quantities of presolar grains.
New analyses, presented in a new study published in the Proceedings of the National Academy of Sciences, show that the stardust from the meteorite formed about 5-7 billion years ago making it the oldest material ever found on Earth. For comparison, the Sun and Earth were created 4.8 and 4.7 billions years ago, respectively. "This is one of the most exciting studies I've worked on. These are the oldest solid materials ever found, and they tell us about how stars formed in our galaxy," Philipp Heck, lead author of the study, Associate Professor at the University of Chicago and curator at the Field Museum of Chicago, stated.
Scientists use a certain procedure to isolate presolar grains from the meteorite's material. "It starts with crushing fragments of the meteorite down into a powder. Once all the pieces are segregated, it's a kind of paste, and it has a pungent characteristic. It smells like rotten peanut butter," Jennika Greer, a graduate student at the Field Museum and the University of Chicago, and co-author of the study stated. The produced paste is dissolved in acid and the grains are isolated.
Then, the research crew is able to determine their age and the type of star from which they derive by measuring their exposure to cosmic rays. "We used exposure age data, which basically measures their exposure to cosmic rays, which are high-energy particles that fly through our galaxy and penetrate solid matter. Some of these cosmic rays interact with the matter and form new elements. And the longer they get exposed, the more those elements form. 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," Prof. Heck added.
The research findings provide new evidence that can contribute in resolving a long-lasting argument: Do new stars form at a steady rate or not? "Thanks to these grains, we now have direct evidence for a period of enhanced star formation in our galaxy seven billion years ago with samples from meteorites. This is one of the key findings of our study," Prof. Heck, concluded.
Sources: Fieldmuseum, BBC, CNN
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