The BBC have just had a set of programmes on the Permian and K-T mass extinctions. So, I’m wondering how big a hit the Earth could take before human civilisation could not survive. Obviously we’re not talking anywhere near extinction-level events. But could we survive a hit by an asteroid with a diameter of 1 km? 2km? Half a km?
I’ll leave it to the experts but under the right conditions (angle, density etc), my guess is that it would be much smaller than half a km. These things are moving really, really fast!
A really great paper on this: http://users.tpg.com.au/users/horsts/chapman4oecd.pdf. It covers six scenarios based on size of the asteroid and where it hits, and goes into a very detailed analysis. Worth checking out.
The author is Clark Chapman, PhD. He’s pretty qualified to talk on the subject - probably more than most folks at the Straight Dope. Home Page for Dr. Clark R. Chapman
It matters a whole lot where the asteroid lands. If it hit the water, it wouldn’t have to be as large, since it would cause a pretty massive tsunami even if it were “just” a few hundred meters across.
It certainly wouldnt have to be 2km across to cause lots and lots of damage. One just 30 meters across, according to Chapman, would cause:
But the earth is a big place. To affect the whole planet and cause civilization-level effects, Dr. Chapman estimates it would have to be at least a kilometer in diameter if it struck land.
Yeah, but like he notes, the Tunguska explosion was bigger than the 30m rock, and it pretty much affected nobody. Even if it hit downtown New York it’d hardly end civilization.
Yep. That’s what I meant to say when I said that “To affect the whole planet and cause civilization-level effects, Dr. Chapman estimates it would have to be at least a kilometer in diameter if it struck land.”
There are lots of theories about the KT, and Permian extinctions. Keep in mind no one really stands willing to say that either of these were caused by singular instantaneous events. For one thing, the KT “event” covers thousands, at least years. It might include the results of the Chicxulub impact and other events, such as the Deccan Traps lava flows. The Permian can’t be narrowed down to anything like all happening during the same million years. That too might have been the results of multiple, and unrelated events, volcanic and impacts.
There is also the possibility that an impact in some area would be far more serious in consequences than in other places. Yellowstone in the central US is a favorite of doom sayers. The combination of a medium impact, and a large change in volcanic activity are fairly powerful effects. Melting large areas of permafrost can cause the release of large amounts of methane, and initiate a cascade of warming.
It should be kept in mind that a century is pretty much instantaneous on the geological scale, and so, your whole life probably won’t include much in the way of major extinction events. Not counting nuclear war, of course.
Tris
I just hope we never have to find out!
There’s lots of interesting stuff there, but what a pity he’s obviously on the end of a dial-up line. I’m getting 4k/s transfer rates.
It could have, if it had hit a city in the US or USSR during a tense period of the Cold War…
Point is, it’s not just the size of the impact that determines whether civilization collapses. It’s also how people respond to it, and that’s a whole lot harder to quantify.
In terms of Human Civilisations Ended Per Unit Mass, I think it’s likely to be more efficient to deliver your asteroid in two or three large chunks, spaced maybe a few months apart - I realise that’s pretty unlikely to happen naturally - after the first strike, there will be crop failures, massive socio-economic upheaval, lots of survivors hanging on in an already-weakened state - follow up with one or two more hits and it could be lights out for humanity.
Or maybe not - I suppose it might actually be true that for some range of masses, the effect is worse than twice as bad as something half the size.
The real problem (unless you are in the impact zone, when you actually don’t have a problem because you are too busy vapourising) is atmospheric dust reducing energy reaching the surface of the earth (nuclear winter effect). Part of the knowing what will happen is whether the equator acts as a sufficient boundary to prevent northern hemisphere/southern hemisphere atmospheric exchange. A northern hemisphere strike is more likely to hit landmass, and thus throw up high altitude dust. However, if this dust has difficulty passing the equator, then Australia/New Zealand/SouthEast Asia, Southern Africa and South America will have a pretty good chance to go it alone.
A Southern Hemisphere strike is more likely to be a splashdown, which gives everyone who lives away from the sea a better chance of survival. Of course, eventually the problem comes down to one of food - crops cannot grow without the sun.
Si
Can a meteorite large enough push the earth out of its orbit?
Well, the theoretical answer is that every meteorite pushes the Earth out of its orbit, only not very much.
The “Mars sized impactor” believed to be responsible for the creation of the moon pushed the Earth into its current orbit, although out of what orbit is hard to say.
The real answer to your non-technical query is, any event, whatever type that could “move the earth out of its orbit” in the way you mean would vaporize the Earth to a great depth, and the resultant cloud of gasses and planetary debris that might reform over millions, if not tens of millions of years.
Tris
Only in the sense that a mass of vaporised rock and fragments may be moving in an orbit that is more eccentric that the earths current orbit.
The energy of impact required would melt and vaporise the planet.
So no, not really
Si