bad astronomy | Asteroid impact burns plants, which can be used to identify craters

Maybe this is just a little obsessive thing but it’s great science too: A team of geologists and earth scientists has discovered a new way to identify ancient archaeological craters: By the way they burned everything around them *.

When a cosmic body such as an asteroid or comet collides with a planet, the enormous energy of its motion is released. Think of it this way: it takes a massive amount of energy to move something quickly, and the bigger/faster it is the more energy it takes. If you stop it, it takes the same amount of energy as well, and if you stop it quickly – like allowing it to reach a planet – all that energy is quickly released.

An asteroid the size of a mountain or even a small hill that moves a dozen or more times as fast as a bullet has a lot of energy. Much. It could easily dwarf a nuclear weapon, or even thousands of them to a large enough effect. The energy of the Chicxulub impact that occurred on the dinosaurs was one hundred million one megaton nuclear bombs. Sure, that effect was near the high end of what we saw, but still. Even a small effect would be really fun.

Oddly enough, it can be difficult to pinpoint the craters left by traces of monsters. Sometimes they are very old and corroded. Or it could be underwater, or resemble other geological events such as volcanoes. Recognizing them in the geological record can be inconvenient.

There are some telltale signs, such as shocked quartz; The mineral is subjected to such stress in the enormous stress caused by the change of the crystal pattern. But this is not always easy to find.

Even smaller pits are tougher. Only about a third of craters less than 200 meters wide have been identified from impacts in the past 12,000 years or so, and because they can significantly impact their local and even regional environments, finding them is important.

So any new method that helps is welcome, and that’s what this new research brings [link to paper].

There are quite a few sure little pits that have coal around – including, for my own good, Heaven’s field In Argentina, which occurred a little less than 5,000 years ago. Campos are popular meteorites on the market, I have a piece the size of my fist and weighs over 1.2kg. Anyway, some of this coal falls into the same geological context where craters and carbon dating indicate similar ages, so the connection seems real.

However, how can you tell if the coal was from an unrelated forest fire, and was not ignited by the massive release of energy from a collision burning a forest?

Studies have shown that the way coal reflects light depends in part on the temperature of combustion of the flammable substance. Coal from low-energy scrub fires is darker than high-energy “crown” wildfires, where flames reach the tops of trees. This indicates that coal created from a collision event must have a higher reflectance than normal fire.

So the researchers went to four different small impact sites: two of the eight related craters called cabbage in Estonia (due to the disintegration of one asteroid upon entry), Morasco Crater in PolandAnd the Whitecourt hole in Canada. It all happened in Holocene, the most recent geological epoch, the period we live in today, and they all have coal deposits nearby in the ejected material. They measured the reflections of these coals and compared them to those from six different wildfires that were of different intensities.

Interestingly, coal from all four impact sites were very similar, despite being from widely separated impacts in time and space. Coal released from fires differed greatly in reflectance, even, crucially, in a single fire.

At first, this may appear to be a problem, especially if the range of wildfire coals overlaps with the range of impacts. However, smoothing the effect of charcoal ends up being beneficial. If you can collect a bunch of coal from a suspected crater, and each piece falls within a narrow range of reflection, that’s a good indication that the filter is an actual crater. Alternatively, if the reflectance values ​​differ on the samples, they are more likely to have formed in a wildfire.

So it is not the value of the reflection per se so much as it varies in the sample that tells the tale. They hypothesized that the twigs and twigs that had fallen naturally from the trees prior to the impact were then buried in a warm substance emanating from the impact, which then burned relatively slowly and turned into charcoal, which is why all the samples are similar to each other.

This is very clever. I will note that this method will likely only work well for recent impacts, geologically speaking, that contain intact coal unaltered by the ravages of time and erosion. However, it can help to identify dozens of recent craters, some of which may have intact traces that can be observed around them.

This would help geologists and planetary scientists better understand the effects of ultrafast impacts. The physics of how it works is still not well understood. And if these effects can be increased, they can help us better understand the larger effects as well. These are rare, but they can have global effects, so the better we understand these active disasters, the better off we will be.


*I don’t think I’ve ever split a double sentence before, but while Strunk and White might somehow credit me here, it works.