A silicon carbide grain extracted from the Murchison meteorite, which fell on a dairy farm outside Melbourne on September 28, 1969, condensed in a dying star roughly seven billion years ago, according to cosmochemist Philipp Heck and his research team at the Field Museum in Chicago.
Dating Stardust From the Murchison Meteorite Fall
The microscopic grain—measuring the width of a bacterium—predates the formation of the Sun by more than two billion years, making it the oldest solid material ever identified on Earth, according to findings published in January 2020. To isolate the material, researchers crushed milligrams of the meteorite, dissolved the surrounding silicates with acid, and analyzed neon isotopes trapped inside the remaining grains. According to PNAS data reported by Heck’s team, the analysis of 40 large presolar silicon carbide grains revealed cosmic-ray exposure ages running from about 3.9 million years to roughly 3 billion years before the solar system formed.
Did you know? The Murchison meteorite fell at 10:58 a.m. on September 28, 1969, producing a sonic boom and leaving an alcoholic, methylated-spirits-like scent in the air, according to historical accounts reconstructed in Meteoritics & Planetary Science.
How Researchers Measured Interstellar Lifetimes
The dating method relies on neon isotopes produced when high-energy galactic cosmic rays strike solid matter during its journey through space, as detailed by researchers at ETH Zurich and the Field Museum. The longer a grain drifts in interstellar space, the more cosmic-ray products accumulate inside its crystal structure. ETH Zurich’s noble-gas laboratory determined that the bulk of the analyzed sample aged between 4.6 and 4.9 billion years old in total duration, with the oldest material reaching seven billion years when accounting for interstellar exposure time.
Pro Tip: When evaluating meteorite exposure ages, scientists must account for variables such as cosmic-ray production rates, grain shielding, and precise size distributions, as noted in the PNAS study.
Evidence of Enhanced Star Formation in the Milky Way
The distribution of grain ages challenged the long-held assumption that star formation in the Milky Way has occurred at a steady pace across galactic history. Instead of a uniform spread, the isotopic data pointed to a distinct surge in star formation roughly seven billion years ago in the stellar neighborhood that later spawned the Sun. According to researchers, these ancient stars swelled, shed dust into the interstellar medium, and left materials drifting until they were swept into the molecular cloud that collapsed to form our solar system 4.6 billion years ago.
Extraterrestrial Amino Acids and Organic Chemistry
Beyond its ancient stardust, Murchison remains one of the most thoroughly studied carbonaceous chondrites due to its rich organic inventory. Within a year of the 1969 fall, Keith Kvenvolden, Carleton Moore, and their colleagues published evidence in Nature confirming the presence of extraterrestrial amino acids within the stone. Subsequent analyses by the scientific community have identified dozens of amino acids, RNA nucleobase components, and sugars such as ribose, demonstrating that prebiotic chemical ingredients can form on asteroid parent bodies without the presence of living Earth biology.
Frequently Asked Questions
How old is the Murchison meteorite itself?
The Murchison meteorite itself is approximately 4.6 billion years old, matching the age of the solar system, while the individual silicon carbide grains embedded inside it date back up to seven billion years, according to Heck’s team at the Field Museum.
What kind of meteorite is Murchison?
Murchison is classified as a CM2 carbonaceous chondrite, a primitive, water-altered class of meteorites that accounts for roughly four percent of observed meteorite falls, as noted by the Meteoritical Bulletin Database.
Where are the Murchison meteorite samples stored today?
Following the 1969 fall across an 11-by-3-kilometer strewn field in Victoria, Australia, samples were distributed to museums and cosmochemistry laboratories worldwide, where institutions like the Field Museum store their stock under nitrogen gas to prevent weathering.
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