Research
Science goes to hell
Important teacher discovery
from Unicamp gets the pages of Science
Luiz Sugimoto
On the Argentine side of the immense Pampas plain, there is an area near the city of Río Cuarto cut by elongated depressions, some five kilometers long and several meters deep. The cause of this phenomenon, on such regular and flat soil, certainly fueled the imagination of the local population for many years.
In January 1992, North American scientist Peter Schultz, recognized worldwide for his studies on meteorites, published an article in the magazine Nature, where he treated these depressions as being the record of the first documented impact of a meteorite at a low angle (grazing). on the face of the Earth, similar to the effect of a 'bomb' launched sub-horizontally. In general, shocks of this type occur at higher angles (greater than 30 degrees). The meteorite would have entered the atmosphere at very high speed (over 20 km per second) and reached the ground at just 5 degrees. After the first shock, the object dismembered and dug into the surface, rebounding twice more and creating new depressions.
It is a rare type of event in nature – and even rarer to be preserved to this day. According to Schultz, it would have occurred between 5 thousand and 10 thousand years ago, being witnessed by ancient inhabitants of the Pampas. To support this hypothesis, the American geologist presented evidence that was difficult to dispute. He found, within the depressions, pieces of meteorites and a very common product of these impacts: “tektites”, the technical name for a glass that results from the shock and consequent fusion of the rocks and soil that make up the Earth's surface.
Peter Schultz's hypothesis, however, has just been challenged in an article published by Science magazine on May 10th. The research leaders are geologists Philip Bland, from the Open University (England), and Carlos Roberto de Souza Filho, from the Geosciences Institute (IG) at Unicamp. Nine other scientists signed the article.
Arsenal – In May last year, this multidisciplinary group arrived in the city of Río Cuarto armed with an arsenal of data. Souza Filho had access to photographs taken by the American spy satellite Corona in the 60s. The Brazilian scientist is also the main investigator of a new scientific satellite, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (Aster), which sees objects with dimensions of up to 15 meters and works with spectral bands that go beyond the visible (it has infrared and separates, for example, water, different types of sediments, vegetation, among other elements of the landscape).
“Schultz had surveyed a restricted area, with just 10 features. By expanding the field of observation through satellite images, we were able to survey 400 additional features, with the same characteristics”, recalls the researcher. “In some of them, we found fragments of meteorites, as well as a significant amount of glass. We thought we had discovered the largest field of low-angle impact craters on the face of the Earth,” he jokes.
But one detail worried them: if the 400 elongated craters were the result of the impact of a single meteor, the directions should converge (radially, as if they were those stylized rays of a sun as the center), which was not verified. Furthermore, these depressions were distributed over a very wide region, which would hardly be generated as a result of a supposedly grazing impact.
Three events – Although the desire to announce the discovery of hundreds of depressions in the Pampas was great, scientists chose to be cautious. They decided to date the ages of the fall of the meteorites, the formation of the glass and the surface of the depressions. With that, they solved a big problem. The meteorites in the region were of different composition and, mainly, of different ages: one of them fell around 36 thousand years ago and another more than 52 thousand years ago. The surface of the depressions is approximately 4 thousand years old, making it quite recent. The glass, not only in the area studied by the American geologist, but within a radius of 800 kilometers, has consistent ages, around 480 thousand years.
“We believe that they are three different and independent events, which Schultz apparently combined into one. In conclusion: none of those features, Schultz’s or ours, are from a meteorite impact”, observes Carlos Souza Filho. “In a way it was a little disappointing, because you never start research with the aim of compromising the work of others, on the contrary, the objective is to add, to better understand the phenomena and expand scientific knowledge”.
How to explain – In search of explanations, scientists looked to the meteorological center of Argentina and surveyed the direction of the winds over the last 20 years. They noticed that the winds ran parallel to the features of each location. They then concluded that the elongated craters were caused by wind erosion, depending on the main direction of the winds. “On a flight from Córdoba to Buenos Aires, you notice these 'scratches' on the ground”, says Souza Filho. Regarding the presence of meteorites within the features, the Unicamp geologist reports that it is common for these interplanetary fragments to fall at a constant rate, across the entire surface of the Earth.
“Meteors vaporize when they enter the atmosphere. The largest ones manage to cross it, reaching the surface in the form of small pieces – in the recent past, one of these meteorites hit a parked car in the United States. This, put over thousands of years, justifies why fragments are found so frequently in the features of the Pampas. Although they fell thousands of years ago, wind erosion was largely responsible for their being exposed today on the Pampean surface – essentially at the base of these depressions”, says the researcher.
Pending issue – An interesting problem remains: how to explain the existence of “tektites”, aged around 480 thousand years, either in depressions or in deep cuts in the ground, within a radius of up to 800 kilometers? The group made two more trips to Río Cuarto in search of the answer. The only plausible explanation, according to the Brazilian professor, is that there really was a major impact almost 500 millennia ago, spreading glass fragments throughout the region.
“There was probably a regional extinction of life in the Pampas, due to the amount of energy released by the impact, but life was gradually reestablished, as more distant areas were not affected”, estimates Souza Filho. Impact simulations investigated by the researchers, also published in Science, indicate that a meteor (or piece of it) measuring 500 to 1.000 meters in diameter would cause this damage, opening a crater at least 5 kilometers in diameter. “Fortunately, the probability of an impact of this proportion occurring on Earth is perhaps once or twice every million years. If it were more frequent, our crises would probably be other than just economic ones”, he illustrates.
The team is preparing a new trip, after carefully re-studying satellite images, now with the aim of discovering the crater buried beneath the recent sediments that cover the Pampas. “We will be back in the next few months”, announces Souza Filho, with a smile like someone who already has a good idea of where the giant meteorite fell..
Research can be seen on TV
This article published on May 10 by Science is a journalistic “scoop” followed by Maverick Television. The British Ministry of Foreign Affairs commissioned this TV production company (which makes documentaries for several broadcasters in that country, such as the BBC) with the task of verifying and filming the participation of English researchers in scientific missions outside Europe.
In addition to Philip Bland, Maverick also invited Carlos Roberto de Souza Filho, from Unicamp's Institute of Geosciences, to the filming that took place in February this year. Science, until the date it published the article, had reserved rights to the results. Now, this documentary will be televised in various parts of the world, including Brazil.
MAGAZINE
Now, Weekly
Marking the beginning of a new moment in the dissemination of the University's institutional, cultural and academic matters — coinciding, not by chance, with the beginning of the new administration — Jornal da Unicamp switches from monthly to weekly periodicity.
The objective is that, by reaching the hands of its readers more frequently, the newspaper will start to inform more and better, keeping less distance from the facts and allowing a more intense monitoring of Unicamp's daily life.
In addition to increasing its effectiveness as a means of information at the service of teaching, research, extension and institutional interest — in addition, helping the university to account for its varied production — the change of pace brings a positive change in its editorial profile. The speed of facts will require shorter texts, will allow for more intense coverage of the production of theses and, whenever possible, advance and commented information on prospective events.
In this context, the four central pages will be dedicated to news of a more internal nature — including the week's agenda — with which Jornal da Unicamp incorporates the A Semana bulletin, valuing it and giving it wider circulation and new treatment.
We hope readers enjoy it and feel free to give their opinion, suggest and participate.
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