A meteorite that fell near the Australian town of Murchison in 1969 was found to contain grains of stardust up to around 7 billion years old — the oldest solid material ever identified on Earth, formed long before the Sun or planets existed.

A stone that fell from the sky over rural Victoria in 1969 turned out to contain something older than Earth, older than the Sun and older than every planet in the solar system.

The Murchison meteorite, officially recorded by the Meteoritical Bulletin Database as an observed fall near Murchison, Australia, on September 28, 1969, is a carbonaceous chondrite. That means it belongs to a chemically primitive class of meteorites rich in carbon-bearing material and partly altered by water on its parent asteroid. It has been studied for decades because pieces were collected soon after the fall and because the meteorite preserved clues from the earliest history of the solar system.

But one of its most remarkable discoveries is older than the solar system itself: microscopic grains of presolar stardust.

In a PNAS study led by Philipp Heck, researchers analyzed presolar silicon carbide grains extracted from Murchison and used cosmic-ray exposure ages to estimate how long those grains had traveled through interstellar space before being incorporated into the material that became the meteorite. The oldest grains in the sample were inferred to have formed about 5 billion to 7 billion years ago, making them the oldest solid material yet identified on Earth.

What stardust means here

Stardust is a poetic word, but in this case it is also literal. Presolar grains are tiny mineral particles that condensed around older stars before the Sun existed. When those stars shed material into space, some of the dust survived in the interstellar medium, the thin mixture of gas and dust between stars. Later, part of that old dust became mixed into the cloud of material that collapsed to form the Sun, planets, asteroids and meteorites.

Most solids in meteorites date from the birth of the solar system about 4.6 billion years ago. Presolar grains are different. Their isotopic compositions do not match ordinary solar system material, which tells scientists they formed in earlier stellar environments. They are, in effect, laboratory samples from stars that lived and died before our own star formed.

The grains in the Heck study were silicon carbide, a hard mineral made of silicon and carbon. They are tiny enough that the largest would still be invisible without magnification. Yet their chemistry carries a record of time spent in space. As the Field Museum explained when the paper was released, researchers can estimate exposure ages by measuring products made when galactic cosmic rays hit the grains.

How scientists dated grains older than the Sun

The method is not the same as dating a rock with uranium and lead. For these grains, the team looked at isotopes of neon produced by galactic cosmic rays. Cosmic rays are high-energy particles that travel through the galaxy. When they strike solid matter, they can trigger nuclear reactions that create new isotopes. The longer a grain is exposed in space, the more of those cosmic-ray products can accumulate.

That gives scientists a kind of exposure clock. It does not tell the full biography of every grain with perfect precision, because the calculation depends on cosmic-ray production rates, grain size and shielding. But it can place real constraints on how long individual grains drifted in interstellar space before they were packed into the early solar system.

The PNAS team reported that many grains were younger than 300 million years in interstellar exposure time, while at least some exceeded 1 billion years. When those exposure times are added to the age of the solar system, the oldest grains reach roughly 7 billion years. That is why the claim is often phrased as “up to around 7 billion years old” rather than as a single exact birthday.

A meteorite as a galactic archive

Murchison is famous for another reason too. Carbonaceous meteorites can contain a wide range of organic molecules, and Murchison has played a major role in studies of extraterrestrial amino acids and prebiotic chemistry. But the presolar grain work asks a different question. It is not mainly about the chemistry that may have fed early Earth. It is about the life cycle of stars and dust before the solar system was born.

The distribution of grain ages also hinted at something larger than one meteorite. The study found many grains with ages clustered in a range consistent with an episode of enhanced star formation before the Sun formed. If that interpretation is right, Murchison contains not just old dust but evidence of a busy period in the Milky Way’s history, when many stars were born and later seeded space with fresh grains.

That makes the meteorite a strange kind of archive. A hand-sized fragment can hold materials from a parent asteroid, chemistry from the young solar system and grains that predate the Sun by billions of years. The oldest pieces are not spectacular to the eye. They are microscopic, acid-resistant minerals separated from meteorite powder in the lab. But their smallness is part of the wonder.

A rock that landed near an Australian town in 1969 carried within it solids made before Earth had oceans, before the Sun had begun to shine and before the planets had assembled. Those grains survived stellar death, interstellar travel, solar system formation, asteroid history and a fiery passage through Earth’s atmosphere. In Murchison, scientists found that the oldest reachable matter on Earth is not a terrestrial rock at all, but stardust older than the world that caught it.