Oldest stuff on Earth found inside meteorite that hit Australia
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[January 14, 2020]
By Will Dunham
WASHINGTON (Reuters) - A meteorite that
crashed into rural southeastern Australia in a fireball in 1969
contained the oldest material ever found on Earth, stardust that
predated the formation of our solar system by billions of years,
scientists said on Monday.
The oldest of 40 tiny dust grains trapped inside the meteorite fragments
retrieved around the town of Murchison in Victoria state dated from
about 7 billion years ago, about 2.5 billion years before the sun, Earth
and rest of our solar system formed, the researchers said.
In fact, all of the dust specks analyzed in the research came from
before the solar system's formation - thus known as "presolar grains" -
with 60% of them between 4.6 and 4.9 billion years old and the oldest
10% dating to more than 5.6 billion years ago.
The stardust represented time capsules dating to before the solar
system. The age distribution of the dust - many of the grains were
concentrated at particular time intervals - provided clues about the
rate of star formation in the Milky Way galaxy, the researchers said,
hinting at bursts of stellar births rather than a constant rate.
"I find this extremely exciting," said Philipp Heck, an associate
curator at the Field Museum in Chicago who led the research published in
the scientific journal Proceedings of the National Academy of Sciences.
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"Despite having worked on the Murchison meteorite and presolar grains
for almost 20 years, I still am fascinated that we can study the history
of our galaxy with a rock," Heck added.
The grains are small, measuring from 2 to 30 micrometers in size. A
micrometer is a one-thousandth of a millimeter or about 0.000039 of an
inch.
Stardust forms in the material ejected from stars and carried by stellar
winds, getting blown into interstellar space. During the solar system's
birth, this dust was incorporated into everything that formed including
the planets and the sun but survived intact until now only in asteroids
and comets.
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![](../images/011420pics/news_k21.gif)
A scanning electron micrograph of a presolar silicon carbide grain,
about 8 micrometers in its longest dimension, from a meteorite that
crashed into Australia in 1969 is seen in this image released in
Chicago, Illinois, U.S. January 13, 2020. Janaina N. Avila/Handout
via REUTERS
![](../images/ads/current/fitzpatrick_lda_SPONSOR_2017.png)
The researchers detected the tiny grains inside the meteorite by
crushing fragments of the rock and then segregating the component
parts in a paste they described as smelling like rotten peanut
butter.
Scientists have developed a method to determine stardust's age. Dust
grains floating through space get bombarded by high-energy particles
called cosmic rays. These rays break down atoms in the grain into
fragments, such as carbon into helium.
These fragments accumulate over time and their production rate is
rather constant. The longer the exposure time to cosmic rays, the
more fragments accumulate. The researchers counted these fragments
in the laboratory, enabling them to calculate the stardust's age.
Scientists previously had found a presolar grain in the Murchison
meteorite that was about 5.5 billion years old, until now the
oldest-known solid material on Earth. The oldest-known minerals that
formed on Earth are found in rock from Australia's Jack Hills that
formed 4.4 billion years ago, 100 million years after the planet
formed.
(Reporting by Will Dunham; Editing by Sandra Maler)
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