The Flensburg meteorite, which fell in 2019, is a scientific treasure from the prehistoric times of our solar system, researchers report. According to their dating, it contains the oldest known carbonates. The carbon-containing minerals were formed over 4.5 billion years ago – and through the action of liquid water, according to the studies. This probably happened on an asteroid or minor planet, the fragment of which the meteorite is. The results therefore fit the theory that meteorites once supplied water to young earth, say the scientists.
A fireball rushed across the sky – accompanied by a bang: In September 2019, a meteorite amazed hundreds of eyewitnesses in northern Germany. Just one day after the event, a citizen of Flensburg found a black stone weighing 24.5 grams on the lawn of his garden and reported the find to the authorities. This is how the little chunk came into the hands of the experts at the Institute for Planetology at the Westphalian Wilhelms University of Münster. They were able to show that it is actually a partially burned-up fragment of the meteorite that caused the celestial phenomenon.
A special example
The mineralogical and chemical investigations then showed what type of meteorite it was: “The Flensburg meteorite is a so-called carbonaceous chondrite – a special and rare form of stone meteorites,” says Addi Bischoff from the University of Münster. This finding brought the little chunk more and more into the center of interest: It could provide clues to processes and material characteristics in the youthful phase of our solar system, when the planets were formed. Because meteorites can be fragments of ancient celestial bodies that once provided educational material.
In the previous analyzes of the Flensburg meteorite, the scientists led by Bischoff have already come across carbonates in the material. These are minerals that are very common in rocks on today’s earth. They arise through geochemical processes or through the activity of living beings that use carbonates in scaffolding structures, for example. Due to the great heat, however, there were no carbonate rocks on the primordial earth when it was formed, the researchers explain. Scanning electron microscopic examinations of the carbonates in the Flensburg meteorite have already led to an interesting finding: The characteristics show that the minerals were formed with the participation of water. In their current study, Bischoff and his colleagues have now investigated the question of when this happened.
Greetings from the youth of the solar system
For this purpose, they subjected the carbonates from the Flensburg meteorite to a dating using the high-resolution ion probe at Heidelberg University. The dating method was based on the decay rates of a naturally occurring isotope – the decay of the long-lived but unstable manganese isotope 53Mn, of which traces are still contained in the material. “The measurements were extremely difficult and demanding because the carbonate grains in the rock are extremely small and precise isotope measurements had to be carried out in a very small space of just a few micrometers in diameter – thinner than a human hair,” explains co-author Thomas Ludwig from the Institute for Earth sciences.
But the age determination was successful: the results show that the carbonates were formed around 4.565 billion years ago. “The most precise dating to date with this method showed that the mother asteroid of the Flensburg meteorite and the carbonates formed only three million years after the formation of the first solids in the solar system,” says co-author Mario Trieloff from Heidelberg University. Thus, they are more than a million years older than comparable carbonates in other carbonaceous chondrite types, say the scientists.
In addition to dating using the radionuclide 53Mn, the tiny carbonate grains were also examined for their carbon and oxygen isotopic composition with the Heidelberg ion probe. As the researchers report, the results provided further evidence of the formation in connection with liquid water: Accordingly, the carbonates were excreted from a relatively hot fluid shortly after the formation and heating of the mother asteroid. “They also attest to the earliest known occurrence of liquid water on a planetary body in the young solar system,” says Trieloff.
Bischoff concludes: “The Flensburg meteorite proves that around 4.5 billion years ago in the early solar system there must have been small bodies on which there was liquid water. Perhaps such bodies also supplied the earth with water, ”says the scientist.
Source: Westfälische Wilhelms-Universität Münster, University of Heidelberg, specialist article: Geochimica et Cosmochimica Acta, doi: 10.1016 / j.gca.2020.10.014