According to their own information, US researchers have identified the oldest material on Earth to date: the so-called presolar granules from a meteorite are roughly five to seven billion years old and therefore older than the Earth and the entire solar system, the scientists report Philipp Heck from the Fields Museum in Chicago.
Our sun was formed around 4.6 billion years ago, the earth around 4.5 billion years ago. The finding suggests that there was a phase of increased star production in our part of the Milky Way around seven billion years ago, the team writes in the journal “PNAS”.
“These are the oldest solid materials, that have ever been found, ”emphasizes Heck in a message from the museum. “And they tell us how stars formed in our galaxy.” His team had examined fragments of the Murchison meteorite that 1969 hit Australia.
Thousandths of a millimeter small granules from the primeval times of the solar system
In the meteorite, the researchers had hoped for presolar material, that is, preserved granules from the primeval Building material for our solar system that had previously been produced by another star that had long since gone out. Such granules are roughly in everyone 20. To find meteorites, but they usually measure only a few thousandths of a millimeter.
The scientists actually found what they were looking for in the Murchison meteorite: they ground a small fragment into a fine powder and dissolved it in acid until only the tiny presolar silicon carbide grains remained. “It's like burning the haystack to find the needle,” explains Heck. Silicon carbide (SiC) makes up only a small part of the interstellar material, and because of its special durability, the researchers used it as an indicator.
To determine the age of the tiny granules, they used a new method: you determined the proportion of a certain type of the noble gas neon. This isotope neon – 21 arises through interaction with the so-called cosmic radiation. This is how astronomers describe a constant hail of subatomic particles that move evenly through space from all directions.
Exposed to three billion years of cosmic radiation
Based on the frequency of Neon – 21 the scientists were able to determine the age of 40 granules. “I compare it to putting a bucket in a downpour,” explains Heck. “Assuming that the rain keeps falling, the amount of water in the bucket tells you how long it has been exposed to it.” It turned out that some of the granules were exposed to cosmic rays for up to three billion years before they were released Formation of our solar system was enclosed and preserved in the meteorite.
The researchers also found a surprising number of young granules that were formed less than 300 millions of years before the birth of the solar system. According to her, this supports the thesis that the Milky Way has not always consistently produced the same number of stars. “There was a time before the beginning of our solar system in which more stars than usual were formed,” emphasizes Heck.
Seven billion years ago, a particularly large number of stars were created in the Milky Way
According to the researchers, these granules only emerge at the end of the existence of certain stars, which must have had about twice the mass of our sun. These stars would have a lifespan of roughly two billion years, so this phase must have taken place around seven billion years ago.
“Some people believe that the star formation rate of the galaxy is constant,” explains Heck. “But thanks to these granules, we now have direct evidence of a period of increased star formation in our galaxy around seven billion years ago through samples from meteorites.” (Till Mundzeck, dpa)