fire after impact??

[RogalDORN88]

So watching a video of a large asteroid striking the earth and the shockwave encircles the earth right? Well after this happens and has incenerated ever single tree and plant, how long could the fires burn? I may not be anywhere near as smart as alot of you guys but... fire needs oxygen. no plant life= no oxygen. How long do you think the fires would rage?

[evilsoup]

I'm pretty sure the fires would run out of fuel before they'd run out of oxygen.

Also, IIRC, over 2/3 of photosynthesis takes place in the oceans, which probably wouldn't be catching fire.

[Sea Skimmer]

If you had an impact so big it set the whole earth on fire, it would also throw so much rock and dust into the air that a huge portion of the earths surface would be quickly buried under anything from several inches to several thousand feet of debris. A good portion of the atmosphere would also be ejected into space. Photosynthesis goes out the window, the sun is going to be blocked out for a long time by the dust. Most fires would burn out in a couple days as most combustion would take place near immediately, a shockwave powerful enough to cause ignition over global distances will also tear everything that can burn apart. Exposed coal seams might burn for a protracted period, months or years until the dead planet ceases to have any O2 left.

[Junghalli]

Let's see if we can put some numbers on this.

http://melts.uchicago.edu/~archer/repri ... te_co2.pdf

Fossil fuel carbon: 5000 Gt
Terrestrial biosphere: 500 Gt
Soil carbon: 1500 Gt
Permafrost methane hydrates: "hundreds" Gt
Ocean methane hydrates: 5-10,000 Gt

So high-end adding all this together gives us ... let's be optimistic and round it up to 20,000 Gt of releasable carbon. Let's compare this to how much oxygen there is in the air to see which is likely to run out first, fuel or oxygen.

This site gives mass of the atmosphere as ~5 X 10^18 kg, or ~5 million Gt.

Wikipedia says Earth's atmosphere is ~21% oxygen, this is by volume but assuming mass is similar that gives us ~1 million Gt of oxygen.

Working from this, burning carbon will create ~3.67X its weight in CO2. So 20,000 Gt of carbon will turn into ~70,000 Gt CO2, consuming 50,000 Gt O2 in the process.

Since this is 5% of my estimated 1 million Gt oxygen in the atmosphere, I think it's a fairly safe assumption that if you burned all the readily combustible carbon on Earth you'd run out of fuel long before you ran out of oxygen.

[khursed]

So watching a video of a large asteroid striking the earth and the shockwave encircles the earth right? Well after this happens and has incenerated ever single tree and plant, how long could the fires burn? I may not be anywhere near as smart as alot of you guys but... fire needs oxygen. no plant life= no oxygen. How long do you think the fires would rage?

That's an excellent question, to which I'd have to say our friend Junhalli nixed the no oxygen part quite admirably, so that being said, the length of time the fires would go on depends on several factors.

For one, the size of the impacting asteroid. But that being said, if you want to have as much fun as I did, go there.

http://impact.ese.ic.ac.uk/ImpactEffects/

Enter size for your impact object, change the figure, and then let your imagination take you on a tour of Armageddon.

It won't tell you how long the fires will burn, however you can have an idea of the devastation.

Remember, if we accept the theory of a mars sized object impact causing the creation of the moon, then the limits of destruction are pretty wide.