WASHINGTON – A meteorite that crashed in a fireball in rural Southeast Australia in 1969 contained the oldest material ever found on Earth, stardust that was billions of years before our solar system was formed.
The oldest of 40 tiny specks of dust trapped in the meteor fragments found in the city of Murchison, Victoria, about 7 billion years ago, about 2.5 billion years before the sun, earth and rest of our solar system formed the explorers.
In fact, all of the dust spots analyzed in the study came from before the solar system – known as “presolar grains” – with 60 percent of them between 4.6 and 4.9 billion years old and the oldest 10 percent more than 5 , 6 years old were billions of years ago.
The star dust represented time capsules in front of the solar system. The age distribution of the dust – many of the grains were concentrated at certain time intervals – provided indications of the speed of star formation in the Milky Way. The researchers indicated star outbursts rather than constant speed.
“I find this extremely exciting,” said Philipp Heck, deputy curator at the Field Museum in Chicago, who led the research results published in the Proceedings journal of the National Academy of Sciences.
“Although I’ve worked on Murchison meteorites and presolar grains for almost 20 years, I’m still intrigued that we can use a stone to examine the history of our galaxy,” added Heck.
The grains are small and measure 2 to 30 microns. A micrometer is a thousandth of a millimeter, or about 0.000039 inches.
Star dust forms in the material that is emitted by stars and carried by star winds and blown into interstellar space. During the birth of the solar system, this dust was built into everything that formed, including the planets and the sun, but has so far only survived intact in asteroids and comets.
The researchers discovered the tiny grains in the meteorite by crushing rock fragments and separating the components in a paste that smelled like rotten peanut butter.
Scientists have developed a method to determine the age of stardust. Grains of dust that float through space are bombarded by high-energy particles, the so-called cosmic rays. These rays break up atoms in the grain into fragments, like carbon in helium.
These fragments accumulate over time and their rate of production is fairly constant. The longer the exposure time to cosmic rays, the more fragments accumulate. The researchers counted these fragments in the laboratory to calculate the age of the stardust.
Scientists had previously found an approximately 5.5 billion year old presolar grain in the Murchison meteorite, the oldest known solid material on Earth to date. The oldest known minerals that have formed on Earth are found in the rocks of the Australian Jack Hills, which formed 4.4 billion years ago, 100 million years after the planet was formed.