December 5, 2020

Found a material older than Earth within a meteorite | Science


On September 28, 1969, a large fireball in the sky could be seen in Victoria, southeast of Australia, which was divided into three fragments before disappearing. Shortly after an impact was felt. It was him Murchison Meteorite, from which up to 100 kilos of material were recovered. Since then, organic compounds and sugars have been found in these rocks that have reaffirmed the theory that the essential compounds for life on Earth came from space aboard meteorites. Now, a new study reveals that these rocks contain even more amazing things.

The largest fragment of the Murchison meteorite is in the Field Museum of Chicago. There, the team of Philipp Heck He has analyzed a portion of this meteorite by concentrating on 40 grains of silicon carbide, a material with a hardness similar to that of diamond. Each piece measures just a few microns, that is, it is a thousand times smaller than a millimeter, but it contains information that dates back to before the Earth, the Sun and the rest of the solar system existed.

One of the analyzed silicon carbide grains seen with a scanning electron microscope.


One of the analyzed silicon carbide grains seen with a scanning electron microscope.

Researchers have analyzed the changes in silicon carbide produced by the impact of cosmic rays whose particles are capable of changing the atomic composition of the original material and which, due to their frequency, can be used as a clock that estimates the age of the sample .

The results show that the majority of the grains analyzed are 300 million years older than the solar system, which was formed about 4.6 billion years ago, and that some of them are 1 billion years older, the authors of the paper highlight, published today in the magazine Proceedings from the US National Academy of Sciences.

“This is the oldest material ever found,” explains Heck in a press release. The expert defines the analyzed matter as “real star dust” and highlights that his analysis allows clarifying how the stars formed in our galaxy, the Milky Way.

According to his team, the tiny “star fragments” analyzed come from a star that was born about 7,000 million years ago during a period of intense star formation. That material was spit out by its star. First he wandered alone through interstellar space and then was buried inside a body of rock, where it was preserved intact for billions of years. That rock or part of it was attracted by the force of gravity of the Earth, penetrated the atmosphere and decomposed into all the fragments of the Murchison meteorite that fell on Australia in 1969. Having found these compounds is a milestone, since most of the Star dust that is deposited in meteorites is shattered by pressure. Only about 5% of known meteorites contain material of this type and their abundance does not usually exceed a few parts per million.

This material points to what was the origin of the solar system even before it existed. “Silicon carbide grains are among the most refractory and resistant materials formed by meteorites called carbonaceous chondrites, such as Murchison’s,” he explains. Josep M. Wheat, meteorite expert of the Institute of Space Sciences (IEEE-CSIC), in Barcelona. “The interest of this work is that the authors demonstrate that the majority of these types of presolar grains are

formed in a type of stars known as asymptotic branch of the giants. This reaffirms a previous study by our group that suggests that our Sun could have formed in the vicinity of stars of this type, ”he points out.

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