A ‘fossil’ meteorite discovered in a limestone quarry in Sweden is unique and distinct from other known meteorites, according to a team of researchers led by Lund University geologist Birger Schmitz.
The Osterplana 065 fossil meteorite: it is 8 x 6.5 x 2 cm large and is surrounded by a grey reduction halo, in the otherwise red limestone; oxygen was consumed when the meteorite weathered on the sea floor; the coin in the image has a diameter of 2.5 cm. Image credit: B. Schmitz et al.
The new meteorite, called Osterplana 065 (Ost 65 for short), turns our current understanding of meteorites upside down, because the type is not represented among present-day meteorites.
“It has a different composition than all known groups of meteorites,” Dr. Schmitz and co-authors said.
The scientists therefore call it an ‘extinct meteorite’ – a sort of meteorite dinosaur. By extinct they mean a meteorite whose parent body was destroyed in ancient times, and which will therefore never again fall on Earth.
Ost 65 was discovered in Sweden’s Thorsberg quarry, source of more than 100 ancient L-chondritic meteorites.
The meteorite appears to be from the missing partner in a massive collision in the main asteroid belt approximately 470 million years ago.
The collision sent debris falling to our planet over about a million years and may have influenced a great diversification of life in the Ordovician period.
One of the objects involved in this collision is well-known: it was the source of L-chondrites, still the most common type of meteorite. But the identity of the object that hit it has been a mystery.
“This gives us a strong indication that, contrary to current perception, the difference between the meteorite flow to Earth 470 million years ago and now may be as great as when comparing wildlife back then to animals of today,” Dr. Schmitz said.
“In our entire civilization, we have collected over 50,000 meteorites, and no one has seen anything like this one before. Discovering a new type of meteorite is very, very exciting,” said co-author Prof. Qing-zhu Yin, from the University of California, Davis.
According to the team, Ost 65 is almost completely altered except for a few hardy minerals — spinels and chromite.
Analyses of chromium and oxygen isotopes in the surviving minerals allowed the scientists to conclude the meteorite is chemically distinct from all known meteorite types.
By measuring how long Ost 65 was exposed to cosmic rays, they established that it traveled in space for about a million years before it fell to Earth.
This timeline matches up with L-chondrite meteorites found in the Thorsberg quarry, leading the team to suggest the rock is a fragment of the other object from the Ordovician collision.
“The discovery in the Ordovician record of a meteorite type that is apparently not falling on the Earth today has important implications,” the scientists said.
“For example, it is possible that the asteroid that produced Ost 65 no longer exists, and there is no source for such meteorites today.”
“The asteroid belt has been evolving through collisions over the history of the Solar System, and many of the original asteroids have undoubtedly been destroyed.”
Ost 65 is significant because it demonstrates that almost 500 million years ago we may have had different meteorites falling to Earth than what we see today.
“Some may be extinct, whereas others, such as the L chondrites, still fall on Earth,” the researchers added.
“Apparently there is potential to reconstruct important aspects of solar-system history by looking down in Earth’s sediments, in addition to looking up at the skies.”
The discovery is reported June 14 in the online edition of the journal Nature Communications.
_____
B. Schmitz et al. 2016. A new type of solar-system material recovered from Ordovician marine limestone. Nature Communications 7, article number: 11851; doi: 10.1038/ncomms11851
Source link: https://www.sci.news/geology/new-type-meteorite-ost-65-03955.html
