With 3.6 kilometers in diameter, around 300 meters in depth and a 120 meter rim, the Colônia crater is a geological formation located in Parelheiros, in the southern region of São Paulo, less than 40 kilometers from Praça da Sé. With the interior littered with sediment and the edge covered with vegetation, this structure remained hidden until the early 1960s, when aerial photos and later satellite images showed its near-perfect circular shape.
Its origin, from the impact of an extraterrestrial body, was only confirmed, however, in 2013, through microscopic analysis of sediments collected at different levels of depth. This study and others carried out later, all of them conducted by geologist Victor Velázquez Fernandez, a professor at the School of Arts, Sciences and Humanities at the University of São Paulo (EACH-USP), have already been the subject of a report by Agência FAPESP.
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New research by Velázquez has now provided even stronger evidence about the impact that the crater produced. An article about it was published in the magazine. Solid Earth Sciences: “Morphological aspects, textural features and chemical composition of spherules from the Colônia impact crater, São Paulo, Brazil”.
“We found spherules inside the crater, at depths of 180 to 224 meters, whose shape can only be explained by the impact of an extraterrestrial body, which generated temperatures in the order of 5 thousand degrees Celsius and pressures in the order of 40 kilobars – equivalent to 40 a thousand times the standard atmospheric pressure”, says Velázquez.
According to the researcher, the fact that the spherules were found inside the crater and not outside is quite rare, because, normally, the impacts eject sediments outwards. “Our explanation is that the energy from the impact turned the existing rocks at the site into a dense, superheated cloud. This material was thrown upwards, froze and fell back into the base of the newly formed crater”, he says.
The sizes of the beads, on their longest axes, range from 0.1 to 0.5 millimeters, with a prevalence of 0.4 millimeters. As for the shape, 44% are oval, 30% have the appearance of a drop, 18% are spherical and 8% have a disk configuration (prolate). The others do not fit these classifications.
“The fact that they are not all spherical is important because it indicates that they cannot be classified as micrometeorites; since these, due to friction with the atmosphere, are always spherical. The oval, disk and drop shapes are especially relevant, because they can only be explained through our hypothesis: the superheated cloud, vertical ejection and subsequent solidification and falling of the material”, comments Velázquez.
Another important information provided by the research stems from the chemical composition of the beads, consistent with that expected for the rocks that make up the crater rim. “Here, it is opportune to highlight, among many other elements, silicon, aluminum, chromium and nickel. The lack of evidence that they received material from the object that impacted the area strongly suggests that this object was a comet and not a metallic or rocky asteroid”, argues the researcher.
But a definitive statement regarding this cannot yet be made. And it would require further research. “Although we don’t know the size of the object, the speed and the angle of incidence, compared to other impacts, we can say that the collision caused devastation with a radius of 20 kilometers. Another aspect that we ignore is also the date of the event, estimated, for the time being, in a range of 5 million to 36 million years in the past”, summarizes Velázquez.
The study was supported by FAPESP through two regular grants: the first on the registration of geological and geomorphological elements in the Crater of Colônia and the second on the geological records in the region granted to the researcher.
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