Science

Comet fragments could have caused the demise of dinosaurs, study results show

The celestial object that collapsed in the Gulf of Mexico 65 million years ago, ending the rule of the dinosaurs, was likely a fragment of a comet that was hurled to earth by Jupiter and the sun, say scientists from Harvard University (USA).

For Amir Siraj and Abraham Loeb, authors of a study on the subject recently published in Scientific Reports, the hypothesis is the one that takes into account the greater number of details associated with the impact. The comet slice, if responsible for the mass extinction, would explain well the chemical makeup of the object, the time of the strike, the size of the crater, and the arrangement of the solar system that triggered the bolide’s fall.

If correct, the discovery will even help rethink current surveillance against cosmic threats that may reach Earth, given that the comets that would be the cause of this type of accident are from remote and relatively under-explored regions originate from space. “The fall of the object must have been an incredible scene, but we don’t want to see it again,” Loeb told the Harvard Gazette, the university’s news agency.

The formation of Chicxulub Crater, 150 km in diameter and 20 km deep, is linked to the most recent major mass extinction in Earth’s history and one of the most severe – it is estimated that three quarters of the animal and vegetable species on the planet did not exist more. Disappeared creatures include non-avian dinosaurs (since birds, survivors are also dinosaurs), flying and marine reptiles, and several invertebrates.

When it fell to Earth, the object not only caused a megatsunami, it also created colossal amounts of dust in the atmosphere, which also triggered a wave of planetary fires. The result would be something like a few years of winter, greatly reducing the amount of sunlight reaching the planet.

There is little doubt about the role of the catastrophe in the mass extinction, although the simultaneous occurrence of major volcanic eruptions in India, which also darkens the sky and changes the climate, may have made the situation in the biosphere even worse (see infographic).

Currently, the most common hypothesis is that the interplanetary hit came from an asteroid, a large piece of space rock from the belt between Mars and Jupiter. The point, however, is that the chemical makeup of the object that sank in the Gulf of Mexico does not seem to match that of the vast majority of asteroids.

The mass extinction meteorite is believed to be a carbonaceous chondrite that trades in offal, an object that has retained the mineral properties it has had since the formation of the solar system, and that would be rich in carbon compounds, volatile materials, and water. “According to our current understanding of the formation process of the solar system, rocks with this composition were formed at greater distances from the sun,” explains Gabriel Gonçalves, doctoral student at the Astrobiology Laboratory of the USP Chemistry Institute.

Hence the suspicion that the culprit would be a comet, normally associated with these more distant regions and with the “correct” composition as far as we know. However, Siraj and Loeb’s calculations show that neither asteroids nor comets could be catapulted at the frequency required to cause the effects observed to date. In the former case, carbonaceous chondrites would only arrive here once every 3.5 billion years; in the second, at least every 4 billion years – the planet is roughly 4.5 billion years old.

However, the picture changes when you consider that comets with a very broad orbit that only pass through the Sun every hundred or 200 years can suffer strange accidents along the way. According to Siraj, Jupiter’s gravity can act on them like it was an arcade button, throwing them near the sun prematurely.

The star’s gravity, in turn, would tear off a piece of the comet and catapult it towards Earth. The frequency of arrival of this type of gravel would be much higher – perhaps once every 250 million years.

“Traditionally, it is believed that the impact was caused by an asteroid because a large amount of a metal called iridium was found at the end of the dinosaur era, a portion normally found in these types of space objects, not particularly comets. We know this from analyzing meteorites from asteroids, ”explains paleontologist Aline Ghilardi from the UFRN (Federal University of Rio Grande do Norte). “To prove or disprove Siraj and Loeb’s study, we need direct samples, remaining fragments of the object responsible for the formation of the Chicxulub crater.”

If the fragments of distant comets are actually linked to events like the dinosaur extinction, it will present a number of challenges for projects to monitor the threat to Earth, Gonçalves says. “They are bodies that are more difficult to see because they are dark and come from distant regions. This makes it difficult to predict their orbits, which become even more complex due to gravitational interactions and rupture events, ”he explains. It’s important to keep your eyes (and telescopes) wide open. We are a family business.

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