Why did Earth end up being the only planet in the solar system with oxygen as a major component of its atmosphere? Why did Mars and Venus get loads of Co2, but earth relatively little? Why is earth the only planet with oceans, lakes and rivers? Where did earth's water come from, and how come the other planets didn't get any? Why did Venus, Earth and Mars never get large quantities of hydrogen in their atmospheres, like some of the outer planets did?
1. I'm not sure of the particulars, but I've heard that the Moon is said to be a big reason Earth didn't end up like Venus. 2. Life helps keep the CO2 levels on Earth down. 3. There's water all over the Solar System. Europa. Saturn's rings. Titan. The Moon. Mars.
As far as i understand how its thought to be at the moment.... Venus was to volcanic, the interior has pumped out sulphur at a stupendous rate, its greenhouse gone mental. All water has long since gone. Mars was just never warm enough as far as i know, the atmosphere was always just too thin to provide a greenhouse effect. (its thought)All 3 planets got water, venus burnt its to crap and mars has its locked frozen beneath the surface. Earth has 2 things thats gives it a big advantage. Life is one, its thought life has massively influenced the formation and makeup of the atmosphere. And the other is plate tectonics, venus has none and mars only little. Plate tectonics produce a carbon cycle and help with very long term stability oh and a third thing, our moon is damn useful, keeping us stable and rolling the seas back and forth
Life. It didn't start out that way, and was in fact rather closer to a Venus/Pluto mix of gasses, with all the oxygen trapped in oxides in the crust. Life started out eating that, and excreting oxygen, which immediately dissolved in the water. It was only once the water was saturated with oxygen, and the surface was completely oxidized where it could be, that atmospheric oxygen began accumulating. Mars didn't especially, or so it would seem. It got a large %age of what there is, but that's not especially much. Venus, I'm really not sure; with a surface pressure of something like 80 atm, I'm surprised the atmosphere of Venus hasn't simply expanded and boiled away, especially given Venus' lower surface gravity. It may have something to do with the sulfuric cloud cover, but I really don't know. It's the only planet with enough volcanism to produce steam with enough atmosphere to keep it liquid with enough distance from the sun to keep it from boiling away. Possibly just volcanoes; it's not like Hydrogen and Oxygen are especially rare in the universe, especially if the supernova shock that hit the stellar nebula that birthed the sun was a Type I, though given how much of the heavy elements we have, it seems that the nebula itself may have been a result of a Type II. Could have been a comet. Other planets did get some, just not liquid. Hell, even several moons got some. Because the outer planets did.
as O2C said, life - its the only known process that allows for free oxygen to exist, oxygen being a very reactive element (99.9999999% of the earths oxygen being bound in its body) once again, life - plants take in CO2 and convert it to O2 - mars' lower gravity, and the lack of magnetic protection also means lighter gases have either escaped or been ablated by the solar wind. a hefty chunk of ther solar system is water, which is where it came from - along with planetary bonding of hydrogen with oxygen. as for lakes and oceans, its likely other bodies have them too, but ours are very much generated by geology - earths in the right region to allow the triple-point of water to exist naturally and is tectonically active. thats still open to debate, especially with the 'hot jupiters', but smaller worlds with weaker magnetic fields are less able to hold onto lighter elements, which has some bearing on it.
Actually, gravity seems to have less than you'd think to do with how much atmosphere a planet has. Titan has a surface atmospheric pressure of 1.5 earth atmospheres, and its equatorial surface gravity is about a 7th of earth's - that's less than earth's moon's gravity! But yet the moon is airless. Pluto is smaller than mercury, but it is believed to have a thin atmosphere. Mercury has none.
At least two moons are larger than Mercury, though I think Mercury is more massive. By radius: Ganymede: 2,631.2 km (0.413 Earths) Titan: 2,575 km (0.404 Earths) Mercury: 2,439.7 km (0.383 Earths)
Cars and factories produced CO2, creating an atmosphere, and Al Gore wants to take that atmosphere away.
Well, it's also a function of temperature (and average particle mass). The gravitational field strength determines the escape velocity. The distribution of particle velocities is determined by the atmospheric temperature and the particle mass distribution. The greater the probability of a particle having an above-escape-velocity velocity, the quicker the atmosphere will "boil off". I had to calculate this during my first year of undergraduate physics. Have a look here.
Ah.. so IOW, smaller planets and moons can hold an atmosphere if they're far away from the sun, but in the hot sun-blasted inner solar system, it takes gravity, and spades of it, to hold onto your hot 'n exited atmosphere. Right?
Actually, Venus has an atmosphere that is 90 times that of Eartn and is mostly CO2. It does have clouds of Sulphur. The atmosphere is too thick and the high concentration of CO2 makes a wicked greenhouse effect that leaves the planet surface at 900°F. Mars at one point had flowing waters. There are unmistakable riverbeds on it's surface indicating that it did have an atmosphere and climate similar to Earth's today. The problem here happened when Mar's core solidified and stopped generating a magnetic feild. It's small size left it's atmosphere vulnerable to the solar winds and it slowly eroded away. Today, Mar's atmosphere is only 10% that of Earth's and water cannot exist as a fluid in such low pressure. There is recent evidence that Mars may have some subterrainian water, though. As far as the Oxygen in the atmosphere thing, As far as I know, Earth's first atmosphere was primarily made up of Hydrogen, Ammonia (NH3), Methane (CH4) and some water vapor. No free oxygen was in the air at this point. Very similar to Saturn's moon Titan. So that means there was no ozone layer, so there was plenty of ultraviolet radiation from the sun and plenty of lightening strikes. Well, when scientist reproduce these conditions in a lab for about week at a time, these molecules detach and reattach in interesting combinations. They actually got nucleic acid sequences... Basically, the precursors of DNA molecules. If they can do this in week in a lab, imagine what nature might do after millions or billions of years? Once the right nulcleic acid sequences formed the first DNA molecules, plants came along and basically put the free oxygen and nitrogen in the atmosphere through photosynthesis. So the answer to your queston is that Earth's unique atmosphere comes from the life forms that populate it. www.nineplanets.org also, google "Urey-Miller Experiments" for more info on Earth's early atmosphere. Great thread!!
^Yep. Earth's magnetosphere is all that is stopping most of the atmosphere being stripped away by the solar wind. Another one of the "lucky" things that went life on Earth's way. If Mars' hadn't lost its magnetic field, as you point out, life on the planet surely wouldn't be that improbable, as many other not-too-unsuitable conditions prevail there.
The other really lucky thing, twofold, with the earth is the moon. It's theorized the Moon was a smaller planet that millions of years ago collided with the earth and in the process transfered most of its iron core to the Earth. This has given earth a much larger magnetic footprint that comparable planets. I htink only Jupiter's is larger that earth's if memory serves. The other side of that is having one fairly large satille has kept Earth's axis stable which has been key to sophisticated life developing here.
IIRC, the closest ratio of size between a primary and its satellite in the solar system is Pluto and Charon, the second closest... is Earth and the Moon. There are bigger moons than ours out there but they orbit Jupiter and Saturn, gigantic planets. Mars's moons are tiny, asteroidal type bodies.
The 13th tribe of Kobol engineered it that way and buried fake evidence that they evolved here for some reason. So say we all.
