The atmosphere was here. We’ve evolved to use it.
Even Europa has a very thin atmosphere, which (for a completely different reason) is mainly oxygen.
About 2 billion years ago (long before multicellular life) cyanobacteria started creating O2 gas as a waste product of photosynthesis.
multicellular organisms evolved to find ways to use this waste product productively, so we incorporated it into how we synthesize ATP. On an unrelated note, I think our bones were made of waste material, single cells would produce calcium as a waste product and eventually life found a way to use the waste product productively by making bones.
As far as ‘why is there an atmosphere’, I don’t really know but here is some info.
ETA: The last few posts weren’t there when I started. Oh well. I typed it so you’re stuck looking at it …
The answer to any “why?” question is ultimately fruitless; each answer merely encourages asking “why?” at a lower level of abstraction. So let’s try to peel the onion for at least a few layers of why.
Life is adaptive to its surroundings. So the answer to any question about “why is biology the way it is?” is essentially: The environment is X, therefore biology must be able to thrive in X or there’d be no biologicals hanging around to ask the question.
Why oxygen & carbon dioxide as the operative chemicals? Because they’re there. The reason your cells use the ATP cascade is that free oxygen is around to drive the reactions. It’s IMO a good bet that life is active on Titan and doesn’t use oxygen for that purpose. Why don’t they use oxygen? Because it isn’t there to be used.
Why specifically 20% & 0.05% atmospheric content vice some other values? In any sufficiently complex dynamical system the values it settles on are effectively random. Or, more precisely, chaotic. With a slightly different history we might have settled at different values today. As has been covered by others, current terrestrial plants and animals are collectively symbiotic in maintaining roughly the current oxygen / carbon dioxide mix, net of volcanic contributions. It was not always so. Atmospheric free oxygen percentages have varied between zero and 35% over the history of the Earth. Ref Great Oxidation Event - Wikipedia .
Why Nitrogen for the bulk has already been covered.
Why the current total atmospheric pressure and temperature? Luck of the draw. The combination of planetary outgassing history, magnetic field, orbital distance from the sun and eccentricity, length of day, etc., all ended up with this much gas of this density at this point in Earth’s history.
Why each specific value of those driving parameters? Luck of the draw. Venus shows that we could have had much more atmosphere which would be thicker & hotter, whereas Mars demonstrates the opposite.
Why are we able to ask these questions at all? Weak anthropic principal. Anthropic principle - Wikipedia Note that the *weak *anthropic principal stands on an impeccable logical footing. The stronger variants of the anthropic principal quickly cross into woo.
I wonder if the OP will remember this thread when he wakes up?
In an ocean perhaps?
Much depends upon what you mean by “air”.
Any atmosphere - and mix of gasses?
The current Earth mix of oxygen, nitrogen, argon, and trace stuff?
Just about every planet has some sort of atmosphere. Eventually they get small enough that it is only traces, and you may end up to the point where individual molecules hardly ever band into one another. (I tend to think an atmosphere should at least be dense enough to obey the gas laws.)
Earth’s atmosphere has had a storied past, and there is some evidence we are on at least our second one. Stars (ie our sun) are quite capable of vomiting up huge gobs of highly energetic matter that is capable of ripping an atmosphere off a planet. So you might not have one.
The Earth’s atmosphere didn’t have any useful levels of oxygen in it until (as noted above) organisms evolved photosynthesis, and starting to emit oxygen as a waste product. Again, as noted above, oxygen is a powerful oxidiser, and thus there was a significant energy source sitting being emitted by these photosynthesising organisms. Evolution has a habit of turning up new organisms that can make use of anything going free - like an otherwise untapped easy energy source. So eventually, and inevitably, things came along that could use that oxygen to power their lives, rather than be powered by sunlight. A few hundred million years later these organism’s descendants crawled out of the sea, and were able to make use of the even greater abundance of free oxygen to power themselves. You are one of these descendants.
Let me try to give a serious answer to the question.
When the earth formed out of the remnant of the gas cloud most* of which went into the sun under gravitational attraction, it was molten, on account of the gravitational energy released and, under those conditions, separated roughly according to density. That is why the core is mostly iron and nickel since they were the heaviest common elements. There are heavier ones but only in small quantities. And the gases separated too. The lightest, hydrogen and helium, went the highest and nearly all of them escaped into space. Then came oxygen, nitrogen, methane, ammonia, carbon dioxide (CO2), and so on. Except for nitrogen and CO2 they were highly reactive and formed compounds with the rocks below. Nitrogen and CO2 are not very reactive and at one time must have made up nearly all the atmosphere.
Then came life. The earliest organisms simply lived off the chemicals present in the ocean, assuming that was where life evolved. Then one organism discovered a way to use solar energy to reduce the CO2 to metabolizable carbon compounds (e.g. glucose) and oxygen. They then re-oxidized the carbon compounds. This turned out to be an enormously successful life strategy, resulting in a massive increase in oxygen in the atmosphere. This was, in fact, the very first environmental catastrophe since oxygen was a deadly poison to the anaerobic orgaisms that made up most of life on earth at the time. Some adapted by evolving aerobic metabolisms, others by hiding in oxygen-free places and perhaps there were other strategies. Since oxygen is still highly reactive, we absolutely depend on photosynthetic organisms (plants) to keep us supplied. There is nothing magical about the 21% oxygen. I once read that it has been as high as 30% (at which any spark will ignite an unstoppable fire) and maybe as low as 15% (at which it becomes very hard to start a fire at all). So 78% nitrogen is just what it happens to be at present. About 1% is in other gases, mostly CO2.
*Why didn’t it all fall into the sun? Because as the gas cloud contracted, a small rotation becomes a large rotation (think of a spinning figure skater pulling in her arms to spin faster) and the centrifugal force (spare me the notices that there is no such thing; in my polar coordinate system there is) leaves a large flat disk of debris most of which eventually collapses into a planetary system. Some of the moons (but probably not our moon) formed around planets in a similar way. I read somewhere that 99% of the mass of the solar system is in the sun, but 99% of its angular momentum is in the planets.
His hangover isn’t going to allow his brain to absorb all that. It’s what happens when you replace air with burning herbs.
Man so do I…
No hangover but the goats are very loud this morning.
I suppose we know what it (air) is, how it got there, and so on. The why bit is pretty tough and, from what I can glean from all the great info in the posts, I think that there is simply no answering that question. It’s a lot like that other question: why are we here?
This all started because of some headline about Cosby flashing by the corner of my eye just as the dog rolled his ball under my feet.
Thanks to all btw for contributing…
To elaborate on the ‘why nitrogen’ question; nitrogen is the fifth most common element in the universe by mass and by number of atoms, but it doesn’t readily form solid compounds - so it is quite likely to be found as a gas in any given planet’s atmosphere. It is known as an atmophile element for this reason.
I see what you did there, trying to steal my thunder. This board isn’t big enough for two people who like to quote the same articles from wikipedia. I challenge you to a duel good sir.
So, it has come to this! A duel it is then, good Sir? My second shall call upon you at noon to-morrow to set the particulars.
You don’t seem to be taking this very seriously, but here’s my two cents.
There is a remarkable amount of dissolved gas in magma/lava. It’s part of the reason some volcanoes explode rather than merely oozing - they’re like shaking a can of soda and then opening it.
I did the math once, and my estimate is that the magma in the earth has enough dissolved gas to replace our atmosphere more than 20 times over. Of course, this would start off with a lot of CO2, SO2, HS and other nasty components that would have to be removed for us to survive it. So, really, the atmosphere we see now is sort of the tip of the iceberg - it’s the the percent left over from the percent originally outgassed.
I thought it was a rotating frame of reference that mattered, rather than the coordinate system used. That is, a polar coordinate system can be desirable from a math perspective, but you’ve still got to have a rotating frame of reference.
Poking around wiki (Use of the term centrifugal force in Lagrangian mechanics)
Centrifugal force - Wikipedia I see that:
"…The left side is a “generalized force” and the first term on the right is the “generalized centrifugal force”. However, the left side is not comparable to a Newtonian force, as it does not contain the complete acceleration, and likewise, therefore, the terms on the right-hand side are “generalized forces” and cannot be interpreted as Newtonian forces.
The Lagrangian centrifugal force is derived without explicit use of a rotating frame of reference, but in the case of motion in a central potential the result is the same as the fictitious centrifugal force derived in a co-rotating frame. The Lagrangian use of “centrifugal force” in other, more general cases, however, has only a limited connection to the Newtonian definition."
So nevermind my comment.
Two questions, two good answers.
You must have somehow skipped all of the people that provided answers to precisely that question.
Though, again, it would be good if we had any kind of damned clue as to what you’re interested in:
-Why does Earth have an atmosphere? Where did it come from?
-Why does modern life need air? What do we get out of it, and what do we do with it?
-Why is our atmosphere made up precisely of the gas mixture we have now?
Or what?
Said another way, it wouldn’t take too much lava flow on a planetary scale to augment the current Earth atmosphere with enough freshly liberated lava gases to overwhelm the current oxygen balance and to boost the pressure until our atmosphere looked a lot like Venus’s. :eek:
Best to hope we don’t have plate tectonics open a really big continental rift anytime soon. A replay of e.g. the Deccan Traps eruption might be enough to finish us off.