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Tom Mazanec
2008-Feb-23, 07:49 PM
Assume life never arose on Earth. What would its atmosphere look like?

JohnBStone
2008-Feb-23, 08:46 PM
Life soup, CHON. Mostly from volcanic outgassing. Mostly CO2, CH4, N2 and a few others. Trace O2. No pure Hydrogen and Helium gas which Earth can't hold on to.

Would the sky still be blue? I don't know.

(Or is this a philosophical question like: if a tree falls in a forest and there is no-one around to hear it...)

George
2008-Feb-23, 10:37 PM
Would the sky still be blue? I don't know.
Probably not. A young Earth would have had an atmosphere twice that of what is observed along the horizon, which appears more white than blue. Also, volcanic pollution would linger much longer in the atmosphere because of the lack of the cleansing effects from oxygen, which were not present before life, apparently.

It is more likely the sky would have been white or yellow-white than any blue color.

JonClarke
2008-Feb-24, 06:27 AM
I suspect it would be N2 with minor CO2, the later being buffered by the atmosphere and rock weathering. Plus the usual traces of noble gases, water vapour, sulphur gases, etc. Without life there would probably be less methane than at present.

I am not sure what role oxygen plays in clearing out volcanic gases, but rain would have been just as effective

Jon

G O R T
2008-Feb-24, 10:02 AM
I suspect it would be N2 with minor CO2, the later being buffered by the atmosphere and rock weathering.

CO2 was buffered by the oceans, leaving huge deposits of carbonaceous limestone. Even so, lots of CO2 was left until life split it or locked it away into various shells. Without life, the CO2 percentage would have remained quite high along with surface temperatures. If the oceans had evaporated CO2 would have built up even higher as seen on Venus.

Tom Mazanec
2008-Feb-24, 03:50 PM
Limestone. Interesting. So there might be caves?

ravens_cry
2008-Feb-24, 08:21 PM
Query, I thought limestone was formed by the shells of life forms over a long, long time, or is that just chalk? Of course the ocean also sequesters CO2 as dissolved in the water, but if the planet heated up, a significant amount of that would be released.

JonClarke
2008-Feb-24, 09:36 PM
CO2 was buffered by the oceans, leaving huge deposits of carbonaceous limestone. Even so, lots of CO2 was left until life split it or locked it away into various shells. Without life, the CO2 percentage would have remained quite high along with surface temperatures. If the oceans had evaporated CO2 would have built up even higher as seen on Venus.

I agree, some CO2 would have been sequested as inorganic carbonate, however I don't think these reactions are as effective as organisms in binding CO2 as biogenic carbonate and organic matter. So the atmospheric CO2 level might have been still higher than it is now. But what the precise level might be I am not sure - a few percent perhaps? Some sort of equilibrium value, I suspect, between uptake of CO2 as carbonate through hydrothermal reactions, weathering, and diagenesis on one handd, and release of CO2 through thermal breakdown of carbonate minerals during metamorphism.

Jon

JonClarke
2008-Feb-24, 09:38 PM
Query, I thought limestone was formed by the shells of life forms over a long, long time, or is that just chalk? Of course the ocean also sequesters CO2 as dissolved in the water, but if the planet heated up, a significant amount of that would be released.

The bulk of terrestrial limestone is directly or indirectly biogenic in origin. But carbonates can also be precipiated inorganically, through evaporation, weathering, diagenesis, and hydrothermal reactions. On a lifeless Earth less processes would be much more evident than they are today.


Jon

George
2008-Feb-24, 09:54 PM
Does dolomite come from an inorganic process?

G O R T
2008-Feb-25, 09:07 AM
Dolomites can crystalize at high temperatures in supersaturated pools where water and magma were in close proximity.

That said, reducing bacteria are thought to play a part in most other Dolomite formation.

ravens_cry
2008-Feb-25, 11:39 PM
The bulk of terrestrial limestone is directly or indirectly biogenic in origin. But carbonates can also be precipiated inorganically, through evaporation, weathering, diagenesis, and hydrothermal reactions. On a lifeless Earth less processes would be much more evident than they are today.


Jon
Thanks for the info, you have been most helpful!

tracer
2008-Feb-28, 10:23 PM
Does dolomite come from an inorganic process?

No, it comes from a bad movie studio (http://www.imdb.com/title/tt0072895/).