Hundreds of glass fragments found in Brazil They are traces of an ancient impact that dispersed them millions of years ago, scientists have discovered.
These drops of material represent the mist of molten rock that liquefied on impact, then cooled and hardened quickly to form pebble-like glass objects, some the size of a pea and others as large as a golf ball, known as tectitas.
The resulting tektite field is one of the few discovered to date, reports Science Alert.
«I was very surprised!» he declared to ScienceAlert geologist Álvaro Penteado Crósta, from the University of Campinas (Brazil). «Tektites are a very rare material on Earth.»
And, fascinatingly, scientists have not yet identified an accompanying impact crater.
Earth’s impact history is much murkier than that of other rocky bodies such as the Moon, Mercury and Mars, indicates Science Alert.
One of the traces of an impact can be tektites, which are formed when a meteorite hits the Earth with enough force to generate temperatures high enough to melt the surface rock.
The area covered by its expansion is known as a scattered field, but these are very rare due to the rapidity with which the tektites degrade: They last only a few tens of millions of years, at most.
The story of discovery begins not with scientific field work or laboratory analysis, but with a resident of Minas Gerais, Brazil. He found one of the strange glass beads, investigated its possible origin and contacted meteorite expert Gabriel Silva of the University of São Paulo, he says. Science Alert.
«Although the photos the resident sent us looked like tektites, at first Gabriel and I were doubtful, since nowadays it is easy to buy tektites from other places, such as Thailand and the Philippines, online,» Crósta recalled. «Also, tektites and obsidian (volcanic glass) can look similar in photos.»
But weeks later a second report came from another resident who lived about 60 kilometers from the first. So the researchers requested some samples. Initial tests suggested that the globules could be tektites; Then, of course, the only thing left to do was go to Minas Gerais in person and look for more.
A huge amount of tektites
More than 600 objects have been discovered. When the article was published, they covered a 90-kilometer-long region in Minas Gerais; However, since then, new finds in the neighboring states of Bahia and Piauí have expanded the known scattered field to more than 900 kilometers, reportedly Science Alert.
These Brazilian tektites have been called geralitasin honor of the state in which they were first identified.
The key to confirming that the glass was of impact origin lay in something it barely contained: water.
Volcanic glasses, such as obsidian, typically contain between 700 parts per million and 2% water. The geraisites contained between 71 and 107 parts per million, indicates Science Alert.
Tektites are almost completely waterless because the extreme heat of an impact (far beyond what a volcano can generate) effectively evaporates almost all of the moisture from the molten rock as it moves through the atmosphere.
Argon isotope dating of the tektites gave a maximum age of about 6.3 million years, a date that could be younger if the impact site contained its own argon. Chemical and isotopic analysis of the geaisites also revealed something surprising about the rocks molten by the impact.
How old are they? The rocks vaporized by the impact were already around 3 billion years when the meteorite hit. They formed during the Mesoarchic era, when the Earth was less than half its current age, says Science Alert.
The elephant in the room is the missing impact crater. The size and shape of the scattered field, as well as the identity of the geaisite parent rock, should indicate approximately where the impact occurred. However, so far, no nearby impact structure of the correct age has been identified.
GML
