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Biggest Asteroid to Hit Earth

Science & Technology

Biggest Asteroid to Hit Earth

The image above is the asteroid Toutatis. It’s just a rock like countless others in the solar system, except that it’s a dangerous one. It is 2.5 kilometers wide, is loosely composed, essentially a conglomeration of rubble, and due to numerous planetary approaches, it has a very chaotic orbit. Moreover, it could someday hit earth. If it did, it could destroy human civilization. In 1992, 1996, 2000, 2004, 2008, 12 and 16, this object made very close passes of earth and will do so again in the coming decades. There is a chance it could eventually hit us. While it’s not likely to ever impact the planet, it’s expected to be ejected at some point from the inner solar system before it likely has a chance of affecting, it does illustrate one of the spooky realities of the solar system. That at any time Earth could be hit by an asteroid or comet.

The Chelyabinsk Event

These events happen routinely on a small scale, meteorites fall on earth regularly, and each year several detections of larger airbursting meteors are picked up, typically over the oceans. Sometimes though, they do occur over land, such as the Chelyabinsk meteorite over Russia, which causes significant damage including broken windows over a large area and even caused the collapse of a brick building.

On a more meaningful, crater forming scale, impacts are less common, but moderate-sized crater-forming-events have happened within the scope of human prehistory, including a recently discovered crater in Greenland that was buried under a glacier. We survived it.

The Cretaceous Period was the last and longest segment of the Mesozoic Era. It lasted approximately 79 million years.

livescience.com

However, huge events that threaten extinction are much rarer, but as the impact that ended the Cretaceous period shows, they do indeed happen, and while unusual, nothing currently stops them from happening again. However, there are efforts to detect near earth asteroids underway, and many objects have been found that have some chance of eventually colliding with earth. These are termed PHOs, for potentially hazardous objects. They further break down into two groups, potentially dangerous asteroids, and potentially hazardous comets. There are currently thousands of potentially dangerous asteroids known, and at least eight short-period comets that come close enough to earth to be considered hazardous. While none are presently slated actually to impact earth, if one did the damage would be beyond catastrophic.

Even small events, such as Chelyabinsk, which was about 20 meters in diameter, produced an airburst detonation 30 times greater than the Hiroshima bomb. An asteroid the size of Toutatis impacting would be utterly catastrophic for life on earth. We can get some idea of what this might be like by looking at the end-Cretaceous or K-T impact. There are some surviving indicators that this impact occurred. The first clue was the discovery of a layer in the geologic record from about 66 million years ago that bears high levels of iridium. Iridium is a rare element on earth’s surface, due to it sinking to the core early in the planet’s history. However, it remains widespread in asteroids. Also found were spherules of formerly molten rock that were created in the impact, along with shocked quartz. Then came the discovery of evidence of gigantic tsunamis around the modern Caribbean, and it was found that the beds get thicker in areas of North and Central America. Finally was the discovery of the crater itself, which has been identified to underlie part of Mexico’s Yucatán Peninsula. This impact would have presented a truly apocalyptic vision. While the exact size of the impactor is not known, it was somewhere between 11 and 81 kilometers in diameter, much larger than Toutatis, and would have unleashed the energy of conceivably hundreds of billions Hiroshima bombs.

The impact instantly vaporized the gypsum ocean floor digging directly into the underlying granite, excavating the crater. From there a megatsunami, estimated at over 100 meters tall, would have devastated nearby coastlines. Oddly, however, the tsunami could have been much, much worse. It was limited by what are believed to have been shallow waters in the area. Had the impact occurred in the deep ocean, it could have conceivably been several miles tall. At this time, there would also have been massive amounts of steam and excavated material being released as the object penetrated the ground. Some of that material would have been ejected out of the atmosphere, only to fall again and possibly cause widespread wildfires.

Subject to the massive shock waves generated by the event, planet earth would have then unleashed volcanism and earthquakes and the atmosphere would have been filled with particulate matter that would hang around for years, all of which may have had secondary roles in the mass extinction of life that followed the impact. Indeed, there is fossil evidence of an immediate mass die-off of animal life in the wake of the impact thousands of miles away from it. The aftermath of the impact, however, would see far more deadly. For over a decade, dust particles from the result hung in the atmosphere, causing dramatic surface cooling, a kind of impact winter. This would have directly affected much of life on earth, but most damaging was the drop in photosynthesis, which in turn severely affected the food chain on earth, though increases in levels of carbon dioxide released from the event may have helped the recovery of what survived of the plants after the dust settled.

Following this would be a period of mass extinction of animal life, where the world would see three-quarters of its plant and animal species go extinct, opening the way for the evolution and dominion of mammals which would ultimately lead to us and our civilization. In a way, we owe our existence to an asteroid impact. However, our extinction could easily come at the hands of an asteroid. Moreover, even small ones could do serious, if not fatal damage to our civilization, if one of the regularly occurring more substantial meteorite falls were to happen directly over a major city.

The Tunguska Event

Perhaps the most famous of these kinds of airbursts was the 1908 Tunguska Event, where an object from space entered the earth’s atmosphere and detonated relatively close to the ground. The explosion felled 2000 square kilometers of forest, but luckily the event occurred over an unpopulated area in Siberia, and there are no known officially recorded deaths of any humans, though it may have killed two people according to unofficial accounts. The reindeer in the area is a different story, charred corpses of hundreds of them were reported.

Tunguska’s yield was roughly equivalent to a massive nuclear detonation, something similar in return to US’s largest ever nuclear test, Castle Bravo, though considerably smaller than Russia’s biggest test, the Tsar Bomba. If Tunguska had detonated over a city, the devastation would have been similar to that of a nuclear war, essentially obliterating anything under it. While evidence of a transient nature for Tunguska has been advanced, it’s not settled if it was, in fact, an asteroid, but instead a comet. However, another incident is inevitable because it went off like a bomb and shot iron meteorite shrapnel all over a mountainside.

In 1947 over, once again, over the massive landmass of Russia, an iron asteroid entered the atmosphere and broke apart. Due to it happening during daylight hours, it was widely witnessed. The impacting fragments and shrapnel from the meteorites did form small craters, but fundamentally the original object effectively blew into more or less tiny pieces. No one is known to have been injured by the fall, but it’s not hard to imagine the damage that could be done to a city if tens of thousands of kilograms of iron fell out of the sky on it. However, this very thing may have happened in the past. Perhaps the most disturbing incident involving falling rocks from space occurred in the year 1490 in China. The information on this one is scant, but there are accounts, generally considered by historians as reliable, of rocks falling from the skies and killing apparently up to ten thousand people. That’s a lot, especially for an airburst meteorite fall that didn’t form a known crater, or leave a ton of meteorites around that we’d still be able to find in weathered condition today. Moreover, one wonders about things like ridiculously sized hail that can occasionally fall on earth.

Small Meteorite Falls Can Be Seriously Dangerous.

However, one particular account sounds very much like a meteorite fall. It describes stones that fell that were the size of goose eggs and smaller ones the volume of water chestnuts. It then goes on to say that more than ten thousand people were killed and that everyone else in the city fled. Until actual meteorites from this event are found, it’s difficult to say for sure exactly what happened in 1490 in China. However, it does stand as a warning sign that even moderate to small meteorite falls can be seriously dangerous locally. It’s unlikely that, for the foreseeable future, we will be able to detect and mitigate these types of occurrence. However, with more significant impacts, we do have hope. While smaller objects like Tunguska would be more difficult to detect, large potentially hazardous asteroids like that which impacted at the end of the Cretaceous are more easily identified and tracked.

While the odds are low, one prediction is that there is a 1 in 10,000 chance of earth being impacted within the next century, on longer timescales it is a certainty that an impact will occur. If we don’t mitigate the threat through detection and deflection of the asteroid beforehand. We are only just recently technologically able to start tracking potentially dangerous near-earth asteroids. However, if an immediate threat presented itself to us, we’re probably not quite yet to the level where we could do much about it, if we had only a few months or years to try. We would have to hope for the best, and those that might have survived the impact would need to trudge on, if possible, through the resultant impact winter and massive global disruption that would occur. Effectively, we’ll either survive, or we won’t, and it’s anyone’s guess if civilization itself would continue.

Science Fiction Has Taken On This Trope Many Times.

Science fiction has taken on this trope many times, dystopian worlds where civilization falls and a new dark ages fall upon humanity. This has happened before in human history, where a level of refinement is achieved… but then conditions change, as it did with the western Roman Empire, the Mayan city-states of Central America, Cahokia in North America, etc. where that civilization can no longer be maintained at its previous level. The people adapt and survive, but the culture as it was does not, and only parts of it make it through to the new paradigm. That might be the case with an Impact event, where a handful of people survive, presumably on canned food stockpiles, but the paradigm change is so significant that many things that once made sense, no longer do.

Impact events are caused by the collision of large meteoroids, asteroids or comets (generically: bolides) with Earth and may sometimes be followed by mass extinctions of life.

sciencedaily.com

There’s not much point to manufacturing much of what we currently use as a civilization if electricity can no longer be generated, for example. Indeed, technologies that no longer work can become a liability in such a case, such as being stuck in a building with electronic locks. At that point, the lock is no longer useful. Then formerly old techniques and technologies must be relearned, such as subsistence farming with manual tools and labor. In such a case, this favors groups that still remember those skills. Same with manual methods of irrigation, building shelters, and so on.

Even what was formerly trash to be discarded can become situationally useful, such as plastic bottles for holding and storing clean water or, also keeping seeds over winter from the mice if they hadn’t gone extinct. When enough dust settles for agriculture to become possible again. But eventually, technology might return, useful things are useful things after all, and humans are on the whole resilient and intelligent, but in the short term the only carryovers to the new civilization might be things like religions, folktales that can be told from memory about how the world once was, perhaps some literature, and so on. Quite a bit of archeological evidence of what happened.

There Are Animals Still Around Whose Ancestors Once Walked With The Dinosaurs.

Alternatively, say we don’t survive, post-apocalyptic earth would be left to its own devices. It’s unlikely that an impact event can eradicate all life on earth. The KT event didn’t; there are animals still around whose ancestors once walked with the dinosaurs, such as the alligators and crocodiles. Alternatively, were dinosaurs in the case of the birds. It’s uncertain why these animals survived, but a clue may lie in that the crocodiles and alligators at least haven’t changed that much from what they were like at the time of the impact. That may mean that these animals are just naturally exceptionally well adapted to living on this planet, even when things aren’t so lovely. Even more resilient are the insects. Even during significant past mass extinctions, they tended to weather them relatively unscathed. Only during the particularly awful end, Permian extinction was they severely affected. That extinction, which ironically allowed for the rise of the dinosaurs, makes the end-Cretaceous extinction look like an amusement park fun ride, yet it’s linked to massive volcanism rather than any single impact event.

That was, however, before we came along with our environmental changes and pesticides, there is currently a mass extinction of insects occurring right now. Look around; this is what a typical day in what a technological mass extinction looks like. However, even if the insects were wiped out, there is still one form of life on this planet that would almost certainly survive. The microbes. It’s thought that they are impervious to most types of mass extinction likely to happen to earth. Except that from the sun as it ages. Nothing can survive the baking of the planet. As a result, even after a significant impact event whatever is left of life on earth would continue to evolve and would result in a changed, but still living world.

Perhaps in the far future, another civilization might arise, this time based on something other than a primate. Maybe not even a mammal. However, all is not lost, we are fast gaining enhanced ability to detect threatening objects. The more we look and catalog these objects, the better chance we’ll have in identifying a problem years before the impact, allowing us to come up with a strategy to avoid disaster. This is possible, there are several hypothetical ways to deflect an asteroid, and the more time you have, the easier it would generally be to deflect the asteroid.

We’ll Have A Full Command Over The Asteroids In The Future.

In the future though, we’ll have a full command of the asteroids of the solar system, and here the potential threat they present to us yields to asteroids and their movements being extremely useful. The first will be to mine them for materials, which we will no doubt do as they stand as a ready source of valuable materials that we can use when colonizing space. Even today, asteroids are being looked at as a possibility for profitable ventures mining precious metals from them. However, in the far future, asteroids may provide us with a means of saving the earth. Over very long periods, asteroids can be used to tug planets into different orbits, including earth gravitationally. As the sun ages, it may be advantageous for us to migrate the earth outward, if we’re still around. Hopefully, we are.

But one last thing about asteroid impacts, it’s recently been found that the frequency of asteroid impacts on earth has doubled over the last few hundred million years.

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