[Maniax]

I'm curious what the long term consequences for the Earth's climate would be in the event of a worst-case scenario comet or meteor strike.  I'm aware of the potential immediate dangers such as the massive tsunamis, earthquakes and eruption of volcanoes that could be caused, not to mention the fiery devastation of the initial impact and subsequent spread of secondary fireballs.  I'm also aware of the potential for a prolonged winter period caused by the high amounts of ash in the atmosphere, but the estimates I've seen for how long this winter could last range from just a few months to over a decade. 

The reason I'm asking is I'm considering writing a story taking place in a post-apocalyptic Earth setting caused by such a massive impact, but I'd like to set it about 100 years after the collision and still have the world be noticeably devastated from the event.  Is this possible? Or would vegetation and animal life recover from everything but a total shattering of the planet in less time than a century? 

[Uchuujinsan]

You can always assume that the impact changed society, and that society created after 100 (or 1000 years if you wish) the kind of earth you like.
But the impact itself will create a lot of opportunity for different species, having a heavy influence on the wildlife during this time, as some dominating species might get (nearly) extinct.

[Colonol Dekker]

If there's anything hollywood taught me, it would be that huge waves would eat up coastal areas, fallout would kill us all. Or Astronauts would try to save us, one normally herioc sort, would nomintate to sacrifice him/herself saving the crew and in turn the whole planet. Alternately watch sliders to see how it panned out

[terran_emperor]

Long term affects?

We're F***ed

[Hellstryker]

Like Uchuujinsan said, depending on the severity of the impact it could've thrown us back to the bronze age. Any comet impact that still has any "effects" after 100 years would likely have killed us all anyway, but then I don't really know anything about the subject... 

[BloodEagle]

If memory serves, comets travel far faster than meteor(oid?)s.

So, if a meteor hits (depending on the size): anywhere from complete destruction to a small amount of survivors that will become nomadic (provided that they aren't vault dwellers) in order to survive.

If a comet hits: the planet melts.*

*I'm probably wrong, though.

::EDIT::

Link:
http://www.youtube.com/watch?v=xB7IHNnyJ00 

[Retsof]

If memory serves, comets travel far faster than meteor(oid?)s.

They both travel pretty dang fast, it all depends on what gravity has done to them.

What if the thing hit right in the pole and messed up the earths axial tilt?  It probably wouldn't take much change to mess up the ecosystem.

[Mobius]

Well comets would bring life...to replace us...I don't think it'd be bad...

[Flipside]

Depends more on the composition of the comet, a very icy comet may have very little non-localised effect, and a rocky one could make one heck of a mess.

[Ghostavo]

http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9

Boom, game over.

[Flipside]

Jupiter is a completely different composition to Earth, it's mostly Gaseous for the upper hemisphere, whereas Earth gets rocky very quickly. If an Ice comet hit Jupiter, it would still leave scars for months, yet the Tunguska Blast of 1910, whilst quite extensive, was hardly end-of-the-world stuff.

People lose track of how much of the Earth can be hit by a large meteorite/comet fragment and not even be noticed, though this is, in part, due to scare-mongering.

[Mobius]

http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9

Boom, game over.

That one impressed me when I was little. We wouldn't have survived such a terrible catastrophe.

[Ghostavo]

Jupiter is a completely different composition to Earth, it's mostly Gaseous for the upper hemisphere, whereas Earth gets rocky very quickly. If an Ice comet hit Jupiter, it would still leave scars for months, yet the Tunguska Blast of 1910, whilst quite extensive, was hardly end-of-the-world stuff.

People lose track of how much of the Earth can be hit by a large meteorite/comet fragment and not even be noticed, though this is, in part, due to scare-mongering.

Tusguska was an insignificant meteor measuring tens of meters long.

Now compare that to a comet at a much higher speed and with a much larger size. The fact Shoemaker-Levy 9 broke into 21 significant fragments and still managed to produce such damage on Jupiter's atmosphere is a testament to the threat they pose.

[Flipside]

Not really, no, Jupiter is one hell of a bigger target, with one hell of a bigger gravity well, Earth's been hit time and time again by large comets, meteorites and all sorts of junk over several millennia. It's still here, and so is life. Even the moon, which is 1/3 the size of Earth, has no atmosphere, water or molten core to absorb the impact, and despite the fact it has been hit by even bigger meteorites more frequently, is still there.

It's not impossible, look at one of the moons of Jupiter for a really bad hit, but then, that was an object caught in a Gravity well something like 9000 times stronger than ours.

[karajorma]

http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9

Boom, game over.

That one impressed me when I was little. We wouldn't have survived such a terrible catastrophe.

I wouldn't bet on that.

http://www.lpl.arizona.edu/impacteffects/

Plug the numbers in for yourself.

The impact would be major, the effects would be global. But enough to kill everyone? Given that we survived Toba without technology I find that a little excessive.

[Mobius]

Well, by "We" I _probably_ meant the ones close to the impact zone...

[watsisname]

Might be of some use:  http://www.lpl.arizona.edu/impacteffects/

Most comets do in fact orbit with higher velocity than asteroids, especially the long-period ones that swing in from the Oort Cloud. The above link says average impact velocities for asteroids are 17km/s, while comets can be mighty speedy at 51 km/s. 

Running a quick simulation with typical values for a comet impacting land (6km diameter object consisting of ice, impacting at 51km/s on sedimentary rock), we get the following:  (Calculated with observer 300km from impact)

Energy before atmospheric entry: 1.47 x 10^23 Joules = 3.51 x 10^7 MegaTons TNT
Transient Crater Diameter: 48.1 km = 29.8 miles
Transient Crater Depth: 17 km = 10.6 miles
Final Crater Diameter: 80 km = 49.7 miles
Final Crater Depth: 1.11 km = 0.687 miles
The crater formed is a complex crater.
The volume of the target melted or vaporized is 920 km^3 = 221 miles^3
Roughly half the melt remains in the crater , where its average thickness is 507 meters = 1660 feet
Visible fireball radius: 98.3 km = 61 miles
The fireball appears 74.5 times larger than the sun
Duration of Irradiation: 1370 seconds
Radiant flux (relative to the sun): 518
The major seismic shaking will arrive at approximately 60 seconds.
Richter Scale Magnitude: 9.7 (This is greater than any earthquake in recorded history)
The ejecta will arrive approximately 254 seconds after the impact.
Average Ejecta Thickness: 1.76 m = 5.79 ft
Mean Fragment Diameter: 2.92 cm = 1.15 inches
The air blast will arrive at approximately 909 seconds.
Peak Overpressure: 853000 Pa = 8.53 bars = 121 psi
Max wind velocity: 697 m/s = 1560 mph


An impact of this sort would indeed be catastrophic, killing anyone within several hundred miles of the impact site within moments.  You ask more specifically for long-term climatic effects, and this is significantly more sketchy.  I'm by no means an expert on the subject but I'd imagine a great deal of extinction would occur from the disruption of photosynthesis due to ejected material blocking out sunlight, and global temperatures would most likely drop a significant amount.  How long and how severe this would be I do not know.  But I do expect life would survive at least on some level, and here you have a lot of freedom for your fictional setting.  Humanity, assuming it survives, would definitely see a drastic change in its customs.  We might function on a more isolated and tribal level, or perhaps we'd attempt to wait out the environmental chaos by living underground and growing our own food somehow.  Just some ideas to consider anyway.

Edit:  Oop, Kara beat me to it. 

[Wanderer]

In worst case... asteroid/comet impact energetic enough could heat the material to vaporize the rock formations into more or gaseous mixture.. Which would scroch, boil and burn pretty much everything on the surface of the planet. Pretty much end game for everything with possible exception of the life formed around black smokers in the deep sea though large enough impact would erase those too.

[Flipside]

Life is becoming more and more resilient to extinction events such as this as it evolves. Look at the Permian event, a vast percentage of life was wiped out, something like 80-90%. The next notable extinction event took out the Dinosaurs etc, but Mammals did pretty well, the next 'niche' of evolution was more hardy against extreme conditions, there were still a lot of extinctions, but not nearly as much as before.

Life adapts, and humanity is the best current option for adaptation, and part of the reason life evolves that way is because of impact events such as this.

[Ghostavo]

Not really, no, Jupiter is one hell of a bigger target, with one hell of a bigger gravity well, Earth's been hit time and time again by large comets, meteorites and all sorts of junk over several millennia. It's still here, and so is life. Even the moon, which is 1/3 the size of Earth, has no atmosphere, water or molten core to absorb the impact, and despite the fact it has been hit by even bigger meteorites more frequently, is still there.

It's not impossible, look at one of the moons of Jupiter for a really bad hit, but then, that was an object caught in a Gravity well something like 9000 times stronger than ours.

But we are disregarding the probability of the impact AND the thread creator asked for the worst-case scenario. 

Damn this thread grows too fast.