WASHINGTON (Reuters) – A meteorite that crashed in southeastern Australia into a fireball in 1969 contained the oldest material found on Earth, stardust that preceded the formation of our solar system in billions of years , scientists said Monday.
A scanning electron micrograph of a presolar silicon carbide grain, about 8 micrometers in its longest dimension, of a meteorite that crashed in Australia in 1969 is seen in this image published in Chicago, Illinois, USA. UU. On January 13, 2020. Janaina N. Avila / Brochure through REUTERS
The oldest of the 40 small grains of dust trapped inside the fragments of meteorites recovered around the city of Murchison in the state of Victoria dates from approximately 7 billion years ago, approximately 2.5 billion years before they formed the sun, the Earth and the rest of our solar system, the researchers said.
In fact, all the dust motes analyzed in the investigation originated before the formation of the solar system, known as "presolar grains", with 60% of them between 4.6 and 4.9 billion years and the oldest 10% with more 5.6 billion years ago.
Star dust represented time capsules dating before the solar system. The age distribution of the dust, many of the grains concentrated at particular time intervals, provided clues about the rate of star formation in the Milky Way galaxy, the researchers said, alluding to stellar birth bursts instead of a constant rate
"I find this extremely exciting," said Philipp Heck, associate curator at the Chicago Field Museum who led the research published in the scientific journal Proceedings of the National Academy of Sciences.
"Despite having worked on the Murchison meteorite and presolar grains for almost 20 years, I am still fascinated that we can study the history of our galaxy with a rock," Heck added.
The beans are small, measuring 2 to 30 micrometers in size. A micrometer is one thousandth of a millimeter or about 0.000039 of an inch.
Stardust forms on the material ejected from the stars and transported by stellar winds, which are dragged into interstellar space. During the birth of the solar system, this dust was incorporated into everything that formed, including the planets and the sun, but survived intact so far only on asteroids and comets.
The researchers detected the small grains inside the meteorite by crushing fragments of the rock and then segregating the components in a paste they described as smelling like rotten peanut butter.
Scientists have developed a method to determine the age of star dust. The dust grains that float in space are bombarded by high-energy particles called cosmic rays. These rays break down the atoms of the grain into fragments, such as carbon in helium.
These fragments accumulate over time and their production rate is quite constant. The longer the exposure time to cosmic rays, the more fragments accumulate. The researchers counted these fragments in the laboratory, which allowed them to calculate the age of star dust.
Scientists had previously found a presolar grain in the Murchison meteorite that was about 5.5 billion years old, so far the oldest known solid material on Earth. The oldest minerals that formed on Earth are found in the rocks of Jack Hills in Australia, which formed 4,400 million years ago, 100 million years after the planet was formed.
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