On the track of ancient meteorite impact craters


Identifying ancient small-scale meteorite impacts is essential to better estimate the risk to which we are subjected. Scientists have just shown that analyzing carbon in sediments could help trace these ancient impacts. Although they are rarely visible, thousands of small meteorites enter Earth’s atmosphere every day. The vast majority, however, will burn up before reaching the ground: these are the shooting stars we observe at night. Only the largest bodies have the ability to impact the ground, such as the Chelyabinsk meteorite that crossed the Russian sky in 2013. Measuring 20 meters in diameter, it fragmented in a powerful explosion over the city of Chelyabinsk, the shock wave caused a lot. of damages The fragments, however, disappeared without much of a trace. Thus, the last crater formed as a result of the impact of a meteorite dates back to the year 2007, when a large asteroid fell on a small town in Peru. If this type of event is relatively rare compared to tens of tons of extraterrestrial material pass through the atmosphere every day, but it can be particularly damaging to infrastructure and populations. In 1908, a large meteorite exploded in the Siberian sky, destroying more than 2,000 km2 of forest. What would have happened if it had fallen on a densely populated area? A persistent threat and difficult to assess This type of disaster reminds us that the fall of an asteroid is one of the natural risks that hover over us continuously, without us we cannot warn. they. However, you need to be prepared for such disasters. However, a good risk estimate requires detailed knowledge of the phenomenon. We have no idea, however, how often small and medium impacts occur. Because if large asteroids leave a lasting mark on the Earth’s landscape, finding the marks of the falls of smaller bodies is much more complicated. Vegetation and erosion, indeed, have quickly erased craters a hundred meters in diameter , preventing us from estimating the number of potentially dangerous impacts over a given period of time. Scientists estimate that during the Holocene period (last 11,000 years), only 30% of “small” craters less than 200 meters in diameter have been identified. How to find the trace of the remaining 70%, especially when no meteorite fragments have been preserved? Therefore, a team of scientists has studied this question and developed a field approach that makes it easier to find the trace of past meteorite impacts, but also to estimate the extent of the damage to the environment. Their results were published in the journal Geology. Charcoal different from that produced by “classic” wildfires By studying the surroundings of several known small craters, the researchers discovered that the material ejected by the impact was associated at each to the coal However, they quickly realized that these were not traces of forest fires that preceded the impact. These remains of coal would have originated from a burning of the vegetation caused by the impact itself. Because this coal shows certain peculiarities. It was formed at lower temperatures than the charcoal produced by classic wildfires, and the deposits appear to be much more homogeneous, which is unusual for fires where fully charred fragments are found mixed with partially burned wood remains. Charcoal associated with “small” meteorite impacts could facilitate the identification and study of ancient craters. This also helps to better understand the nature and extent of damage based on the size of the asteroid. Essential data if we want to implement preventive measures.
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