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I was certain somebody would have asked this before, but after scrolling through the Similar questions list I couldn't find any duplicates.

For this question, let's say that an asteroid or comet similar to the one theorized to have caused the extinction of dinosaurs has struck Earth in the modern day. The dinosaurs (as well as 3/4 of the planet and animal species) were killed from an impact winter, due to dust forming and blocking sunlight.

Could we prevent a massive extinction like this using modern technology? For this question, it's too late; the asteroid has already collided with the planet. Can we figure something out, or are we all already doomed?

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I'm looking at this concept because I'm wondering how feasible such an event is for my story, but I want to know just "how dead" we'd all be.

Clarification: This question isn't about saving humanity, it's about saving as much life (animals, fish, birds, etc) as physically possible, so building space stations to escape won't work here. Because the creatures left on Earth would all mostly die off, which is still a massive extinction event.

Additional clarification: This is happening in the real, modern world. So the dinosaurs are already dead, I just used "Dinosaurs" in the question title to specify the type of extinction-level event in a way most people are already familiar with.

Humanity has as much time as they can use before dying off.

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    $\begingroup$ I think the answer depends somewhat on the timescales involved. It'd take us a long time to change the orbit of an 81km wide dino-smasher, even if we tried really hard. Also short deadlines mean lots of panicky people doing stupid things at cross purposes. So maybe give a few more details? $\endgroup$ – Starfish Prime Sep 25 '19 at 21:40
  • $\begingroup$ The asteroid has already hit the planet by this point. $\endgroup$ – overlord Sep 25 '19 at 21:44
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    $\begingroup$ We seem to have a misunderstanding here, you posted this in the sandbox 3 hours before posting it here. The sandbox is not an "instant-solution-granted" option. Honestly, If you post something there, and you've got some useful suggestions after a week to improve your question, then that's more along the lines of what you can expect. Posting it there and then immediately posting it here doesn't help you or anyone else. $\endgroup$ – Tantalus' touch. Sep 25 '19 at 21:49
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    $\begingroup$ If the asteroid has already collided, my understanding is that the main cause of widespread death of plants (which causes widespread death of animals) is similar to nuclear winter where a lot of soot and other aerosol particles get kicked up into the stratosphere, significantly dimming the light from the sun for a few years (see the 'Aerosol removal timescale' section of the wiki article). With modern technology I doubt there's a way to artificially accelerate this process by a large amount or no one would worry about nuclear winter. $\endgroup$ – Hypnosifl Sep 26 '19 at 0:02
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    $\begingroup$ I don't see how this query is anything but clear. Am I missing something? I think it could be argued that this story based, however. $\endgroup$ – elemtilas Sep 26 '19 at 3:16
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You are asking if, once the impact has happened, we can do something to fix the situation. Let's see what we are supposed to fix:

The impactor was large enough to create a 190-kilometer-wide (120 mi) peak ring, to melt, shock, and eject deep granite, to create colossal water movements, and to eject an immense quantity of vaporized rock and sulfates into the atmosphere, where they would have persisted for several years. This worldwide dispersal of dust and sulfates would have affected climate catastrophically, led to large temperature drops, and devastated the food chain.

Let's look more in detail

The re-entry of ejecta into Earth's atmosphere would include a brief (hours-long) but intense pulse of infrared radiation, cooking exposed organisms

Nothing we can do here, since it happened immediately after the impact, when at best people would be either unaware or stitched to the tv to see the newsflash.

A paper in 2013 by a prominent modeler of nuclear winter suggested that, based on the amount of soot in the global debris layer, the entire terrestrial biosphere might have burned, implying a global soot-cloud blocking out the sun and creating an impact winter effect.

the impact would have created a dust cloud that blocked sunlight for up to a year, inhibiting photosynthesis. The asteroid hit an area of carbonate rock containing a large amount of combustible hydrocarbons and sulphur, much of which was vaporized, thereby injecting sulfuric acid aerosols into the stratosphere, which might have reduced sunlight reaching the Earth's surface by more than 50%, and would have caused acid rain. The resulting acidification of the oceans would kill many organisms that grow shells of calcium carbonate. At Brazos section, the sea surface temperature dropped as much as 7 °C (13 °F) for decades after the impact

Dropping temperature, practical halt of any vegetation growth including crops. Add to this the onset of panic and the consequences of the huge tsunami which would have swept most of the coastline, destroying all naval infrastructures. The dust dispersed in the atmosphere would also make air transport more difficult if not impossible. But I doubt that there would be much solidarity between countries.

It would take at least ten years for such aerosols to dissipate, and would account for the extinction of plants and phytoplankton, and subsequently herbivores and their predators. Creatures whose food chains were based on detritus would have a reasonable chance of survival, however.

Plants gone, cattle gone with them. We have just some sparse detritivore.

For a comparison, look at the region of Japan struck by the tsunami in 2011. It's still being rebuilt as of today, after 8 years, and it is backed up by an entire country with a stable economy and a stable supply of resources. In this scenario we are taking away the country, the stable economy and the stable supply of resources.

Wrapping up, in the most optimistic hypothesis there will be some humans who will manage to survive. But they won't be able to do anything to mitigate the consequences of the impact. We are simply too puny to be able to even make a dent in such a thing.

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  • $\begingroup$ Note the impactor would have also set off every volcano, landslide, and fault line with even mild stress building up, Its not one tsunami but one mega-tsunami and normal tsunami almost everywhere else. If you live on the coast, you're f*%$ed. $\endgroup$ – John Sep 26 '19 at 14:44
  • $\begingroup$ @John Would the yellowstone super volcano erupt as well? $\endgroup$ – Trevor Sep 27 '19 at 17:07
  • $\begingroup$ @Trevor almost certainly, it is currently under decent pressure. If the impact was roughly a quarter of the way around the planet it might not but it would be a coin toss, the location on the opposite side of the planet will get a new volcano just from the shockwave coalescence. $\endgroup$ – John Sep 27 '19 at 19:04
  • $\begingroup$ @John well that kills my idea for an answer :( $\endgroup$ – Trevor Sep 30 '19 at 15:55
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Someone could prepare for the possibility of such an event happening in the future in several ways.

1) Search for possibly Earth-crossing asteroids and study their orbits to calculate when and if they might someday collide with Earth. Thanks to people like Eugene Shoemaker we are already doing that.

2) Discuss ways and methods of diverting asteroids calculated to impact on Earth. We are doing that already.

3) Prepare for a failure to divert an incoming asteroid, and for other types of possible potential extinction events, by building arcologies.

An arcology is a structure that could serve as a potential ark to save humanity by containing an entire artificial enclosed ecosystem inside. The goal of an arcology would be to totally recycle all of the matter inside so that all the waste matter is turned into useful matter to be reused for the inhabitants.

So a moon base totally separated from the outside vacuum on the Moon would be an example of an arcology. And of course a moon base like arcology could be built anywhere, on the Moon, on Mars, on an asteroid, on a moon of another planet, in a totally constructed space habitat, etc., etc., with various modifications to the design to allow for local conditions.

And a moon base like arcology could be built on Earth, of course.

And if ensuring that mankind survives a potential extinction event on fragile little Earth by colonizing the Solar System so that Earth is not the only place where humans live is a goal, then building moon base like arcologies on Earth as practice for building arcologies on other worlds and in space habitats makes a lot of sense.

Practice makes perfect, as they say, and no doubt it will take a lot of practice to gradually prefect moon base like arcologies so that they are self sufficient, or at least self sufficient enough that the amount of resources they need to gather in outer space via asteroid mining, etc., will be doable.

So no doubt a lot of practice building arcologies on Earth will be necessary for the design of sufficiently self sufficient arcologies for outer space. So once the first few sufficiently advanced arcologies are built on Earth, at least the populations of those arcologies would survive an extinction level event (except for those arcologies that were two close to the impact and were destroyed).

And once the first few sufficiently advanced and self sufficient arcologies are built on Earth and in space, it would be logical to pass laws strongly encouraging more and more people to move into self sufficient arcologies on Earth and in space. As more and more people move into such moon base like arcologies a larger and larger proportion of Earth's population will be more or less safe from an extinction level impact or other type of terrible disaster.

The eventual goal would be to have everyone on Earth live in a moon base like arcology so that they would have no need of an outside ecosystem and could survive a massive asteroid impact or a super volcano eruption or other terrible natural disaster. Of course everyone living in outer space would live in a moon base like arcology until and unless some worlds in the Solar System are eventually terraformed to have a naturally habitable environment.

So it should be obvious that the way to prevent the extinction of all life on Earth, or at least all humans, is to begin preparing for a giant asteroid collision or a super volcano eruption or other natural extinction event before it happens, and even before it is first calculated to happen at a specific future date. It is best to prepare for such an event when no such event is predicted for specific future date, in order to have as much possible time to prepare in before that event happens.

It is better to begin preparing years instead of months before it happens, decades instead of years before it happens, centuries instead of decades before it happens, and millennia instead of centuries before it happens.

So if a giant asteroid sneaks past our detection system and strikes Earth unexpectedly, the proportion of the human race that survives will depend on on long and how well humans have been preparing for the general possibility of a catastrophic natural disaster.

Reacting to a specific asteroid that is predicted to strike hours, days, weeks, months, or years in the future will save only a tiny proportion of the population who could be saved if people begin preparing for the general possibility of such a disaster decades, centuries, or millennia before they know about that specific asteroid.

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The impact winter is just one of the problems when it comes to survive and the other problems will destroy most human infrastructure, so humans won't be able to save themselves, let alone the ecosystems.

1) The big explosion: Everything in the continent where the rock fell is gone, on fire or crumbling. If it fell on, say, Poland, everything from the Rhine to Moscow is on fire or demolished by the shockwave. 2) The earthquakes: The energy imparted to the planet will trigger some quakes, some of them at very bad places, like the Christmas Tsunami in Indonesia. 3) The volcanos: some volcanos will erupt, damaging even more regions. Maybe St.Helens and Fuji will erupt, damaging what wasn't damaged by the explosion, the quakes and the tsunamis. 4) The pyroclastic cloud. The hot dust cloud will spread around the planet. It will be quite hot and will cook some parts of the world, triggering firestorms.

In the end of the first year, most human infrastructure is gone. The survivors are starving, diseased and desperate. They won't save the ecosystems.

To survive mankind would need to prepare itself, after detecting the rock, calculating it's trajectory. You would need a global authority overriding the national governments. The area where it will fall must be evacuated, it's infrastructure moved to safer places, for example, for the polish asteroid, to Australia, the Brazillian Highlands and South Africa. Bunkers must be built in elevated, geologically stable area, above the estimated tsunami lines. The nuclear power plants must be deactivated and their fuel rods stockpiled in safe places to fuel the NPPs that will be built in the safer regions. Food must be stockpiled, Oil must be stockpiled. In the month before the impact you must move as much people as possible from the most dangerous areas, because you need a lot o people to run an industrial civilization. The ones that won't be moved should at least be given local bunkers, some food and oil supplies and long range radios. In the days before the impact, the ships must be in the high seas, the further from continents the better, so that at least some ships survive the waves. You will need the nuclear submarines to transport small cargos and rescue teams, the carriers to carry helicopters and the merchant ships to carry cargo.

About the ecosystems: you will need vaults, in the safe regions. Seeds will be stockpiled so that when the impact winter relents the plant life can be reseeded. Animals will be more difficult: you need a minimum number of breeding pairs to avoid imbreeding, so saving big animals will be almost impossible. You will want to save as much insects, lizards, birds and small mammals as possible. There is no way to save the megafauna. Your bunkers in Australia will have zoos, where the fauna will live. Cloning may be useful for oviparous animals.

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We could save some animals, however it would mean not prioritising saving highest number of humans

The crucial moment is when and where the asteroid (comet) hit. If the impact was a while before harvest, the official mankind reserves would last for a few months of normal usage. Yes, we can eat most of farm animals and go vegan, to become more calorie efficient. We can also start food rationing and most of people, not only in first world, have some reserves in form of fat tissue.

However, if that's supposed to work for a while, then the better prepared countries (richer and food exporters), would have to decide whether to try to feed the third world. It would be a bit nasty to decide that keeping a herd of elephants has a higher priority than thousand inhabitants of for example Kenya. While it maybe possible (maybe shipping there would not be technically feasible anyway), let's say you need some less than idealistic people in charge in that key moment.

As extra thing to worry about, we would first face impact (presumably tsunami or mass fires), then sudden temperature decrease. Let's say that in first days we would have different priorities.

EDIT: If we have a repeat of K/T extinction, then I'd say that we as a specie would survive.

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I'm going to change your question a little bit and assume we have a few years to prepare. Without preparation, there's pretty much nothing we can do post-impact. The seed vaults at places like Svalbard will preserve whatever seeds they already have, but everything else is doomed. Even those preserved seeds likely are too, because the plants they grow into probably require symbiotes that did not survive; some species of plants are only pollinated by a single species of insect for instance. If that insect goes extinct, the plant has at most one generation left. With all this in mind, a better question is how could we prevent the extinction if we did have time to prepare.

I would hope we would try to deflect or destroy the asteroid, but in the event that was untenable, we would need to build dozens of seed vaults containing many examples of every plant we remotely care about. Then, we also need dozens of underground zoos, stocked with enough food and water for ~50-100 years, maybe longer. In these zoos, we have small populations of every animal we remotely care about. These zoos also need to be large enough to allow some species to roam and interact with each other. It does no good to keep lions alive if they all forget how to hunt. We also should save as much genetic material from the current populations as possible, so we don't lose species to genetic bottle-necking. Oceanic life is mostly on its own; we simply don't understand the reproduction of most species well enough to maintain a captive population. Hopefully most of it will survive anyways.

Once the dust has settled, and the climate has started to stabilize, we send out teams to see what's survived. Then, we begin carefully reintroducing the preserved species, starting with the most fundamental plants. The fewer other species a species relies on, and the more resilient it is, the sooner it gets reintroduced. Eventually after a century or so, you will have what amounts to game reserves, separated by vast expanses of ashen wasteland. After maybe a thousand years or so, the world will look mostly normal to the untrained eye. You will never save every species though. Some will certainly die out in captivity, and others will fail to be reintroduced.

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