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Ignoring the fact that we need water in order to survive, what would happen if all of the "oceans" on Earth were filled with a dense non-reactive gas (e.g. xenon or sulfur hexafluoride) instead of water.

Specifically, would the gas stay in the ocean basins, or would it mix with the the rest of the atmosphere? Additionally, how would this affect the weather patterns on Earth?

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    $\begingroup$ We would die of thirst? $\endgroup$ – Serban Tanasa Mar 30 '15 at 22:22
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    $\begingroup$ Is there water anywhere on Earth? $\endgroup$ – HDE 226868 Mar 30 '15 at 22:22
  • $\begingroup$ Yes, there can be water. It doesn't really matter. Mostly I was wondering if the dense gas would mix with the atmosphere or not. And if so, how thoroughly would it mix? $\endgroup$ – Ethan Strider Mar 30 '15 at 22:45
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One of the more defining properties of water is the amount of energy it can hold...it takes a significant amount of energy to warm up a degree or two, but moreover, it takes an incredible amount of energy to change states. This gives our atmosphere a buffer against extreme temperature changes...a little too much energy in the system and the water asorbs this by either warming a little or by changing states from ice to liquid and liquid to gas. Reversely, not enough energy/too much cold, and the water shifts from gas to liquid and then into ice.

Xenon is a gas within our normal temperatures and as such, the process of freezing or vaporizing is not an option. Instead, all the energy is directed towards warming this Xenon up. The end result here is extremely warm xenon during the day and extremely cool xenon during the night (effects exaggerated by summer/winter). During the day time, the mixing of the xenon with surrounding gases would be decently pronounced, simply because of how hot the system gets.

Specific heat capacity is the term for how much energy is required for a 1 degree in temperature change for a given mass of a substance.

Specific heat for Xenon 158.32J/(Kg K) Specific heat for Water ~ 4120 j/kg k

So the first thing to note here is what warms up our ocean in the daylight by 5 degrees would warm up this xenon by well over 100 degrees.

Heat of fusion (energy to melt 1 gram of ice) is 334 j/g (note the units...this is J/G when the above values are j/kg). The energy required to melt 1 gram of ice would raise the temperature of 1 gram of xenon by approximately 2113 degrees.

I'm really not sure what this would do to weather patterns, but you'd get into a setup where this ocean is warming and cooling on the surface by several hundred degrees during the day and night cycle alone...makes life all xenophiles or non-existent.

Edit to address comment:

  • yes, the gasses will separate (to some degree at the surface), however it's not a 100% separation. Sulfur Hexafloride is an extreme greenhouse gas (of all gasses tested, it actually ranks number 1 in that category, about 24'000 more potent than CO2). It does have an elongated life span in the troposphere and stratosphere...so even when concentrated at the ocean level, some of it will still be found in the upper atmosphere. It's all diffusion rates which vary pending temperatures, I think sulphur hexafloride would separate quite well though. It's actually water soluable to some degree, so it'll be in with the water at the surface of the ocean too.

  • As per above comment...sulfur hexafloride is one strong greenhouse gas...it'd likely act as an insulation layer above the water keeping it warmer during the evening hours.

  • Above all water is a bit hard to justify...high lying bodies of water might not have the layer of xenon/sulfur hexafloride on it as it's all migrated down to the oceans.

  • Both sulfur hexafloride and xenon are not electrically conductive...might make for some weird thunder/lightening activities.

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  • $\begingroup$ Excellent answer! What if there was enough water on earth to maintain a relatively similar climate; however, there was also a layer of xenon, or sulfur hexafluoride over the top of every body of water. Would the dense gas cause the water to stay warmer for longer? How significant is the mixing of the dense gas with the surrounding gases? This sulfur hexafluoride boat experiment indicates that there can be a strong separation between the normal atmosphere and a dense gas. $\endgroup$ – Ethan Strider Mar 30 '15 at 22:38
  • $\begingroup$ Tried to answer the comment in an edit in my answer. You will see pretty good seperation between the two by the looks of it. $\endgroup$ – Twelfth Mar 30 '15 at 23:06
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    $\begingroup$ @EthanStrider - Revisiting an old answer with a new comment - I'm pretty sure the oceans absorption rates of this Sulhpur will ultimately result in an acidic ocean (sulphuric acid and all) that would be extremely devastating to any marine 'shell' life that depends on calcium and other 'basic' materials. Coral, mussels/clams, crabs, and lobsters are likely no goes here, along with the life that depends on these for food sources. That said, nature finds a way and there might be a different mineral set that can be used for shells. $\endgroup$ – Twelfth Jul 18 '17 at 17:46
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Our weather is heavily influenced by water evaporating over the oceans and then raining over land. If we had oceans of a dense non-reactive gas, this cycle simply wouldn't exist since nothing would evaporate.

Continents would be a barren wasteland of mostly rock. You would not even see sand or smaller particles because this is the effect of erosion caused from running water. The only life you would see, assuming life could form from this gas, would be constrained to be near the coast, in the gas, or on the bottom. The fact that it is a gas means that a lot of it would "splash up" on land, so you could potentially see this life up to a kilometer away from the coastline.

However, for the most part it would be an inhabitable planet.

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The Oceans are a huge piece of regulating temperatures across the earth Most of Europe would get colder and so would Alaska and Washington state. The gases would mix, but the heavier gases would likely be thicker the farther down you go into the 'ocean' basins. There wouldn't be a 'shore' other than maybe where it starts to get difficult to breath, likely vegetation would change which would be a demarcation of when to stop going forward. There also wouldn't likely be much for rain causing many other issues.

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  • $\begingroup$ This sulfur hexafluoride boat experiment would certainly indicate that there can be a strong separation between the normal atmosphere and a dense gas. However, I have no familiarity with the gas, so if the container is left uncovered, does the sulfur hexafluoride dissipate or stay in the container? $\endgroup$ – Ethan Strider Mar 30 '15 at 16:40
  • $\begingroup$ @EthanStrider that was awesome. Though I would expect some mixing at least around the edges. Convection currents will stir stuff up to some extent I would think $\endgroup$ – bowlturner Mar 30 '15 at 16:44

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