Earth after life

[Balanchine]

Let's suppose that virtually all animal and plant life were quickly obliterated from planet earth. And that this included the oceans down to the level of algae and most plankton. Let's also assume that bacteria would survive in soil and wherever else it managed to find a foothold.

How long would the atmosphere survive?
Are there bacteria that produce oxygen, and if so, would it be enough to sustain human life?
If there were humans able to survive - in salt mines, etc. - would they survive on whatver oxygen remained in the atmosphere, and for how long? (this is also probably a weather/chemistry question too, I'd imagine)

Just curious. Thanks for any input.

An obvious non-biologist,
Balanchine

[mith]

http://student.britannica.com/comptons/ ... atmosphere

And 20% is oxygen.

[Balanchine]

Thanks for the link. I see registration is required to read the article, which at this point I'm declining to do... I appreciate your taking the time to reply, though!

[mith]

You don't need it, this is the first line of the preveiw


The total mass of the atmosphere is estimated to be some 5.5 quadrillion (55 followed by 14 zeros) tons (4.99 quadrillion metric tons).

[Balanchine]

Thanks again, Mith... that's a pretty heavy load, I agree. I was just wondering how long it would last if there were no plants to resupply the oxygen, and if there were any bacteria that do and would contribute to the oxygen supply.

[mith]

Well most oxygen is produced in the ocean by plankton (blue-green algae?) which aren't really plants. So no, we'd be in fine shape.

[Balanchine]

I'd sort of kind of figured that might be the case. But what, then, would happen if all that algae were gone? Would the existing 20% oxygen in the earth simply remain as it is in the atmosphere? If, say, a million humans survived to try and re-populate the planet, how long would it take them to use up that 20% (leaving aside for the moment the question of where they'd get their food). I wonder....

Thanks again, Mith, for replying.

[mith]

I was going to do a rough calculation considering how much oxygen people breathe per minute...but then I realized that most oxygen is used in other ways---bacteria, other animals, combustion...etc etc.

http://answers.yahoo.com/question/index ... 223AAK0sWQ

But assume 1 person = 30g/hour

Lifespan = 500000 hours ~ 57 years

Then lifespan consumption ~ 15000kg

You can support around 7 * 10^10 people for 57 years. or around 1million people for 70,000 years.

Of course these numbers are grossly inflated, I'd assume some sort of industrial activity and at least some forms of life present to provide food etc...

[Balanchine]

Mith.... you are the person!

thanks.
B

[mith]

Man, I am the man.

[canalon]

although you have to take into account that human dies way before the O2 level reach 0%. I am not really sure how much would be fatal, considering that if the depletion is slow enough it gives us time to adapt, just as when living at high altitude, but I suspect that we might all be dead long before half the O2 has been used.

[Balanchine]

Good point, Canalon, and thanks for responding. Like Mith, you are also The Man. But I'm still wondering about any changes to the 02 over time... does sunlight, for instance, break down oxygen? Would it be absorbed by anything else in the environment - those dead seas, the rocks and earth, etc.?