Scientists have now found a new way of finding where asteroids have impacted a planet in the planet's distant past, and the secret method involves charred plants and forensics.
The findings of this study, published in the peer-reviewed academic journal Geology, offer a crime-scene forensic approach to studying where small asteroids have struck the Earth throughout its long history.
In order to best protect the Earth from asteroid impacts in the future, it is important to fully understand how impacts happen.
Asteroids: Making an impact by making an impact
Asteroids often manage to make quite an impact when they smash into the Earth. However, the popular conception of asteroid impacts is typically one of gigantic rocks hundreds of meters wide alighting on fire as they head through the atmosphere.
However, most asteroid impacts are rather small.
How does this all impact Earth?
Earth has extraterrestrial material like rocks and minerals entering the atmosphere on a regular basis. Some of these are even larger like meteors or asteroids. However, most of this is incredibly small and ends up burning up in the atmosphere.
When an asteroid or comet is large enough, it will slam into the Earth at high speeds, passing through the atmosphere and resulting in massive explosions and the formation of gigantic craters.
But there are smaller asteroids that survive the trip through the atmosphere long enough to still make an impact, thus forming a crater.
Though they are small, they can still be dangerous. On average, the craters formed by these small asteroids are under 200 meters wide. If that were to hit a densely populated city, it could cause significant damage.
What have scientists found?
Scientists have a good idea of how many crater-forming asteroids struck the Earth over the last 11,000 years, but only 30% of impact sites have ever been found.
Part of the problem behind this is that unless there were iron meteorite fragments present, there was no way to differentiate these asteroid impact craters from normal natural land structures. This study may have found another way in the form of charcoal.
CSI Asteroid: Using forensics to find charcoal formed by asteroid impacts
Charcoal is often formed when plant life is set on fire. In nature, this is often caused by naturally occurring wildfire, and the makeup of the charcoal can vary depending on the intensity and source of the fire. Asteroid impacts, for example, can cause enough heat to create charcoal.
This raises the question: Is charcoal made from asteroid impacts different from charcoal made from wildfires?
To answer this, the scientists studied four small impact craters: Two in Estonia, one in Canada and one in Poland. The charcoal fragments found were then compared to charcoal formed in six different wildfires, with various other factors like the age of charcoal all being accounted for.
The conclusion is that there was certainly a difference between the charcoals. In particular, the charcoals formed by the asteroid impacts, despite being geographically far apart and occurring at very different time periods, are all very similar.
They aren't identical, and there isn't a single charcoal particle that can be determined as being definitively formed by an asteroid impact, but there are enough similarities.
This may be the key to better identifying small asteroid impact craters and is important as it can play a major role in planetary defense.
While this study doesn't necessarily contribute to stopping asteroid impacts from happening, it does pave the way to finding out something almost as important: Evacuation range.
What damage have asteroids caused to Earth in the past?
Asteroid impacts can cause massive devastation, with the Tunguska event in the early 1900s causing devastation on an enormous scale throughout Russia. Luckily it struck mostly unpopulated areas, but had it hit somewhere more densely populated, the outcome would be far worse.
This information about charcoal formed by asteroid impacts can help give a better idea about the range of how bad such an impact could be, thereby helping to determine just how many people would need to be evacuated ahead of an asteroid impact.