What would happen?. . . A planet with no rain cycle.

[Magnetic]

If the world lost it's ability to evaporate water, condense, and rain, . . . what would we expect to see, in terms of the planet's ecosystems? Would there be a few spots where natural springs would create oasis areas, or without rain, would they eventually dry up as well?

[Guardsman Bass]

If the water stayed liquid near enough to the surface in order for plant-life or the equivalent to take from it, it's possible that you could still have a fairly basic ecosystems. Or, since there is no evaporation, life would still survive in bodies of water, or near them.

For example, the Atacama Desert region in Chile has an average rainfall of less than .004 inches per year, with occasional periods where the area will go without rainfall for years at a time. Some areas in the desert, in fact, haven't seen rain in over 400 years. Still, life survives there in certain places where plants with very deep burrowing tap roots can get to water belowground.

However, the loss of precipitation would still mean mass extinctions, particularly since without precipitation, there are no rivers of any sort. On the bright side, at least water would stay where it was - the lakes wouldn't simply evaporate away.

In the long run, the Earth would eventually probably lose the oceans and the like.

[darthkommandant]

Complete and total extinction of all life forms species. Bascially you get a planet like mars in that it is totally sterile.

[Guardsman Bass]

Complete and total extinction of all life forms species. Bascially you get a planet like mars in that it is totally sterile.

Only in the long run, and that's a maybe. Remember, he said that, for some reason or another, there is no evaporation either, so presumably the water in stagnant bodies like the oceans and lakes would either stay where it is, or ultimately all flow into the ocean, where they would stay. You could still have plenty of plant life in the oceans, and if you had some bodies of water either underground or above ground that didn't flow into the seas, there could still be land life.

[AMX]

No evaporation would mean
a) all water flows to the lowest areas (oceans) and stays there. No springs or anything.
b) extinction of all higher plants (and all animals that eat them), since the water transport inside them is driven by evaporation.

Oceanic ecosystems should be mostly unaffected, though.

[Havok]

No evaporation would mean
a) all water flows to the lowest areas (oceans) and stays there. No springs or anything.
b) extinction of all higher plants (and all animals that eat them), since the water transport inside them is driven by evaporation.

Oceanic ecosystems should be mostly unaffected, though.

A giant stagnant pool of water? I don't imagine too much would survive in it long except for bacteria.

[GrandMasterTerwynn]

If the world lost it's ability to evaporate water, condense, and rain, . . . what would we expect to see, in terms of the planet's ecosystems? Would there be a few spots where natural springs would create oasis areas, or without rain, would they eventually dry up as well?

We all die. The only two ways you could break the hydrological cycle would be to get the planet so hot that water evaporates but never condenses in a fashion that permits the water to return to the planet's surface, or to get it so cold that water doesn't evaporate in any meaningful quantities.

In the case where it's hot enough to break the hydrological cycle, you're looking at a runaway greenhouse effect. At least until all that water vapor is gradually broken down into hydrogen and oxygen by the action of solar ultraviolet radiation. Continental areas dry out in fairly short order, and even the oceans will gradually shrink and become increasingly hyper-saline. Complex life dies out, and the world is ruled by extremophile bacteria and archea. At least until the planet gets hot and dry enough to kill them too.

In the case where it's cold enough to break the hydrological cycle, you're faced with a world where even the oceans (and especially the oceans) are locked under deep ice-sheets. Again, almost all complex life, save for life which evolved around undersea volcanic vents, would die off and the rest of the world would be dominated by extremophile bacteria.

[Einhander Sn0m4n]

Oceans have a lubricating effect as well, enabling plate tectonics. Without plate tectonics, the 'sink' half of the Carbon Cycle breaks. Unfortunately, vulcanism still puts out carbon in the form of CO2, contributing massively to the greenhouse effect. Most planetary carbon therefore stays in the atmosphere as a monstrously thick and heavy layer of CO2, and the temperature skyrockets, quickly destroying what little ocean is left. We'd then have another Venusian world.

The event that is thought to trigger this is large amounts of water vapor rising up into the stratosphere above the ozone layer, where it gets dissociated by UV rays. This is called the Wet Stratosphere phase.

[AMX]

A giant stagnant pool of water? I don't imagine too much would survive in it long except for bacteria.

Not stagnant - the big ocean currents are driven by density changes caused by sunlight, and there's still wind moving the surface.

@Einy & GMT: I believe Magnetic has an "act of plot" or "by magic" scenario in mind, not a "realistic" scenario...


Oh, and I just remembered: No evaporation means that most land-living animals die from heatstroke, since their cooling system doesn't work anymore.

[Lord Zentei]

How would this take place? No evaporation and no condensation of existing bodies of water is a pretty incredible scenario, after all. The specifics may be important.

Otherwise, if the water that is already in liquid form survives, I see no reason why large lakes and seas should not be able to continue to support life. Small lakes and pools would eventually be drained by land-based animal life, and this would eventually die off along with most land-based plants.

[Junghalli]

We all die. The only two ways you could break the hydrological cycle would be to get the planet so hot that water evaporates but never condenses in a fashion that permits the water to return to the planet's surface, or to get it so cold that water doesn't evaporate in any meaningful quantities.

Actually, there is a third imaginable but vastly less plausible way as well: remove all dust and other solid particles from the atmosphere.
For rain to occur atmospheric vapor must condensce around a grain of solid matter, or condensation nuclei. If you were to somehow sweep the atmosphere completely clean of particulate matter and keep it that way there would be no more condensation nuclei for raindrops to form around. This could, perhaps, be accomplished by having a planet which has no volcanoes and whichs surface is completely covered by a smoothly polished layer of some extremely hard material that is almost totally impervious to wind and water erosion.
The effect of this would probably be that water would evaporate but wouldn't condensce back, except as surface-condensation events like dew and frost. I'd imagine all the planet's water would quickly (on a geological time scale) disappear, and the planet would become completely covered with an incredibly thick layer of clouds that would throw the surface into perpetual dim twilight. Needless to say, it would not be a very hospitable environment for life.
I have no idea how such a planet could come to be though.

[Lord Zentei]

I have no idea how such a planet could come to be though.

Even if it would come to be (a sterilized artificial planet built by some hyperadvanced civilization, perhaps), it would not remain so, since there would still be meteor impacts. Moreover, you would have to ensure that it was geologically dead as well.