A new way to identify old asteroid impact
Two methods were available before to help assess the size of impactors some of which may have led to the disappearance of species like the dinosaurs, or even exercised a considerable influence on the climate of our planet. The first and simplest, was based on measuring the crater of impact. But its application is fraught with many difficulties which relativize accuracy. Thus, its diameter is not function of the mass of the meteorite, but also the speed of it at the time of impact. Moreover, if the object fell from the ocean years (70% of the land surface), identification is difficult when the track was not completely eliminated by the subduction of the seafloor. As for terrestrial craters, they are also subject
to erosion, as well as movements tectonic.
The second method involves the concentration of iridium at the site of impact. Iridium is a metal heavy present during the formation of Earth, but later migrated to the nucleus so that it is almost completely absent from the surface. In fact, almost all of iridium found was made by meteorites and its rate is proportional to the importance of falls. Unfortunately, the observed values are variable and researchers must work on averages, which reduces measurement accuracy.
The track of osmium
Some meteorites but differ in their content of osmium, a bluish-gray metal of high density (22.57 grams per cubic centimeter). This is where the meteorites type chondrites, which form 80% of the body hitting the Earth. In these space rocks, the ratio between isotopes 187 and 188 of osmium is very low, much lower than in the water sea When these cars hit our planet, it is largely vaporized and Part of osmium diffuses into the oceans, reducing the gap. The measurement of these two isotopes should therefore help identify the trace of an impact in the layers of sediment and hence the date. On this basis, an international team led by astronomers from the University of Hawaii (Francis S. Paquay, and Gregory E. Ravizza, Tarun K. Dalai) worked on cores collected from two points of the globe to study the sediments corresponding periods of -65 million years (limit of Cretaceous - Tertiary) and -35 million years (late Eocene). This study confirmed the existence already foreshadowed significant impacts at these times, the first of which may have caused the extinction of dinosaurs.
It is likely that research will come from start to lift the veil on certain facts hitherto remained obscure. Thus, if the impact of there 65 million years has resulted in significant changes in the ecology of land and the destruction of many species, two others occurred at least 35 million years without causing disappearances . A better understanding of the size of the projectiles will certainly bring new answers.
New data but also new questions
Another question raised by the study: the meteorite fell in the late Cretaceous period would not exceed, according to new measurements, 6 kilometers in diameter when we previously thought to be 10 to 19 kilometers. It remains possible that some of osmium remained trapped somewhere, but it will still conduct further studies to confirm this result. This is not the first time that the size of an asteroid is thus lowered. The Tunguska meteorite had already suffered a weight loss on the part of a research team led by Mark Boslough, funded by Sandia 's Laboratory-Directed Research and Development Office.
The second method involves the concentration of iridium at the site of impact. Iridium is a metal heavy present during the formation of Earth, but later migrated to the nucleus so that it is almost completely absent from the surface. In fact, almost all of iridium found was made by meteorites and its rate is proportional to the importance of falls. Unfortunately, the observed values are variable and researchers must work on averages, which reduces measurement accuracy.
The track of osmium
Some meteorites but differ in their content of osmium, a bluish-gray metal of high density (22.57 grams per cubic centimeter). This is where the meteorites type chondrites, which form 80% of the body hitting the Earth. In these space rocks, the ratio between isotopes 187 and 188 of osmium is very low, much lower than in the water sea When these cars hit our planet, it is largely vaporized and Part of osmium diffuses into the oceans, reducing the gap. The measurement of these two isotopes should therefore help identify the trace of an impact in the layers of sediment and hence the date. On this basis, an international team led by astronomers from the University of Hawaii (Francis S. Paquay, and Gregory E. Ravizza, Tarun K. Dalai) worked on cores collected from two points of the globe to study the sediments corresponding periods of -65 million years (limit of Cretaceous - Tertiary) and -35 million years (late Eocene). This study confirmed the existence already foreshadowed significant impacts at these times, the first of which may have caused the extinction of dinosaurs.
It is likely that research will come from start to lift the veil on certain facts hitherto remained obscure. Thus, if the impact of there 65 million years has resulted in significant changes in the ecology of land and the destruction of many species, two others occurred at least 35 million years without causing disappearances . A better understanding of the size of the projectiles will certainly bring new answers.
New data but also new questions
Another question raised by the study: the meteorite fell in the late Cretaceous period would not exceed, according to new measurements, 6 kilometers in diameter when we previously thought to be 10 to 19 kilometers. It remains possible that some of osmium remained trapped somewhere, but it will still conduct further studies to confirm this result. This is not the first time that the size of an asteroid is thus lowered. The Tunguska meteorite had already suffered a weight loss on the part of a research team led by Mark Boslough, funded by Sandia 's Laboratory-Directed Research and Development Office.
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