Murchison meteorite grain dated to 7 billion years, oldest solid material on Earth
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A silicon carbide grain from the Murchison meteorite has been dated to roughly 7 billion years old, making it the oldest solid material ever identified on Earth. The grain, which condensed in the outflow of a dying star, predates the Sun by more than 2 billion years. The meteorite itself fell on a dairy farm near Murchison, Victoria, in 1969 and was quickly retrieved under contaminant-free conditions.
The Murchison Meteorite
On the morning of 28 September 1969, a bright fireball exploded over Murchison, Victoria, scattering stones across a field at least 11 kilometres long. Residents heard a sonic boom and smelled a sharp, alcoholic odour as fragments fell. Farmers and children collected pieces by hand; two brothers, aged 10 and 11, recovered about a third of the total mass. A local farmer took samples to a newspaper, which contacted the University of Melbourne the next day, ensuring the meteorite reached a laboratory while still fresh. Murchison arrived just as clean laboratories were being prepared in the United States for Apollo lunar samples, giving scientists a contaminant-free environment to study its organic-rich interior.
The Presolar Grain
The grain is a silicon carbide crystal about the width of a bacterium. To extract it, researchers crushed a piece of the meteorite and dissolved nearly everything with acid, then read the neon isotopes trapped inside to determine its age. The measurement showed the grain condensed roughly 7 billion years ago, over 2 billion years before the Sun formed. Led by cosmochemist Philipp Heck of the Field Museum, the team published the result in January 2020. No older solid material has ever been found on Earth.
What's Next
Scientists plan to examine more presolar grains from Murchison and other meteorites to refine models of stellar evolution and nucleosynthesis. It remains unclear whether grains even older than 7 billion years exist elsewhere in the solar system's debris.
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Murchison meteorite grain dated to 7 billion years, oldest solid material on Earth
