On the trail of ancient meteorite impact craters

On the trail of ancient meteorite impact craters

On the trail of ancient meteorite impact craters

Identifying old small-scale meteorite impacts is essential to better estimate the risk we are subject to. Scientists have just shown that charcoal analysis in sediments could help trace these ancient impacts.

Although rarely visible, thousands of children meteoritesmeteorites Enter theatmosphereatmosphere land every day. The vast majority will still be consumed before reaching the ground: these are the falling starsfalling stars that we observe at night. Only larger bodies have the ability to hit the ground, such as the Chelyabinsk meteorite that crossed the Russian sky in 2013. With a size of 20 meters in diameter, it fragmented in a powerful explosion over the city of Chelyabinsk, the shock wave that caused a lot of damage. The fragments, however, disappeared without leaving many traces. Therefore, the last crater formed following the impact of a meteorite dates back to 2007, when a asteroidasteroid tall came across a small village in Peru.

While this type of event is relatively rare compared to the tens of tons of extraterrestrial material that cross the atmosphere every day, it can be particularly damaging to infrastructure and populations. In 1908 a large meteorite exploded in the Siberian sky, seatseat more than 2,000 km2 of forest. What would have happened if it fell on a densely populated area?

A persistent threat that is difficult to assess

This type of disaster reminds us that the fall of an asteroid is one of the natural hazards that constantly loom over us, without our being able to prevent them. However, you need to be prepared for this type of disaster. 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 the large asteroids leave an indelible mark on the Earth’s landscape, finding the traces of the falls of smaller bodies turns out to be much more complicated.

In fact, vegetation and erosion have rapidly erased craters about a hundred meters in diameter, preventing us from estimating the number of potentially dangerous impacts in a given period of time. Scientists estimate it in the period HoloceneHolocene (last 11,000 years), only 30% of the “small” craters less than 200 meters in diameter have been identified. How to trace the remaining 70%, especially when no meteorite fragments have been preserved?

A team of scientists then examined this question and developed a field approach that makes it easier to find traces of past meteorite impacts, but also to estimate the extent of damage to the environment. Their findings were published in the journal Geology.

Coal other than that produced by “classic” forest fires.

By studying the surroundings of several known small craters, the researchers found that the material ejected from the impact was always associated with coal. However, they quickly realized that these were not traces of forest fires that preceded the impact. These traces of coal would have come from a vegetation fire caused by the impact itself. Because this coal shows some peculiarities. It was formed at lower temperatures than the charcoal produced by classic forest fires and the deposits are much more homogeneous, which is not usual in the case of fires where there are completely charred fragments mixed with partially burned wood remains.

This characteristic of coal associated with “small” meteorite impacts could make it easier to identify and study old craters. This also helps to better understand the nature and extent of damage depending on the size of the asteroid. Essential data if we want to implement preventive measures.

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