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Tom Mazanec
2014-Apr-05, 05:06 PM
AFAIK the Earth's hydrosphere is added to by water coming up from the mantle in volcanoes, and subtracted from by water in the upper atmosphere being photodissasociated (hydrogen leaving). Correct? If so, which process dominates?

eburacum45
2014-Apr-05, 10:20 PM
Subduction is also an important process, so water disappears into the crust as well as coing out of volcanoes. If I understand it correctly, the fraction of our planet which is covered in continental landmass increases over time, so I would expect that the hydrosphere is diminishing (or possibly just getting smaller in extent and deeper).

Rocky1775
2014-Apr-11, 04:03 AM
AFAIK the Earth's hydrosphere is added to by water coming up from the mantle in volcanoes, and subtracted from by water in the upper atmosphere being photodissasociated (hydrogen leaving). Correct? If so, which process dominates?

My recollection is that the Earth's magnetic field prevents the solar wind from sweeping away hydrogen the way it did with Venus. I don't know if the actual loss from the Earth is zero.

Noclevername
2014-Apr-12, 08:59 AM
There may be a net gain rather than a loss; Earth is constantly bombarded with many tons of space dust, which has been shown to contain water.

http://www.space.com/24422-solar-wind-makes-water-star-dust.html

grapes
2014-Apr-12, 10:31 AM
There's also all those ice meteors hitting the earth, right? :)

ETA: OK, comets: http://m.huffpost.com/us/entry/3684406/

publiusr
2014-Apr-12, 03:38 PM
Louis Frank seemed to think we were getting nailed by them all the time ;)

ravens_cry
2014-Apr-13, 06:43 AM
I've heard the sun is heating up, so, in billion years or so, even before the sun enters the red giant stage, it'll be all gone unless we move the Earth out.

Barabino
2014-Apr-13, 06:39 PM
It sounds like moving the whole chest to the car, instead of just putting the socks in the drawer...

science-fiction-wise, it's much more feasible to move down some icy meteoroids than to move up the earth...

Noclevername
2014-Apr-13, 08:36 PM
It sounds like moving the whole chest to the car, instead of just putting the socks in the drawer...

science-fiction-wise, it's much more feasible to move down some icy meteoroids than to move up the earth...

But real-science-wise, a few tiny bits of ice won't significantly affect the Earth's temperature.

The total amount of solar heating the Earth's surface receives would still continue to increase.

Noclevername
2014-Apr-13, 09:22 PM
There may be more water inside the crust waiting in the wings to come up: http://en.wikipedia.org/wiki/Ringwoodite

If the mostly-granite continents are getting bigger, it means light material is still rising from the interior of the planet.

icefoxen
2014-Jun-10, 05:07 AM
This is a great question, and one that we don't really have a full answer to yet. As far as we can tell the amount of water on earth's surface has remained vaguely consistent, between all the fluxes in and out. Earth does lose some hydrogen to solar wind, but it's way way way less than Venus does because of Earth's magnetic field. Water does come out of volcanoes and get subducted back into the mantle, but if we make the (flawed but maybe useful) assumption that Earth's mantle is more or less at equilibrium with the surface, then over long periods the mantle will be releasing about as much water as it absorbs. But we don't really know that much about water in the mantle yet (even how much there is), so this factor is sort of the big unknown in the equation of Earth's water balance.

Ara Pacis
2014-Jun-11, 06:59 PM
Don't forget that humans mine water and bring it to the surface. Also, we create more water every time we burn methane or perform other chemical reactions that result in H2O. We also lose water every time we perform chemical reactions that break that molecule.

Barabino
2014-Jul-13, 07:46 AM
for example, a concrete building absorbs hundeds of cubic meters of water...

for the human point of view it's a gain: a building has much more value than water... but for the ecology, it's a loss... :-/

after centuries, the building will be just debris, but its water will be removed forever from the cycle of rain, food etc...

http://img4.uploadhouse.com/fileuploads/19566/195661346d97712d3cc9af679d99556ed6032d1c.jpg

Centuries ago, somebody wanted to live on an island in a swamp plagued with malaria... not a good idea...and as a matter of fact around 1000 AD they gave up... but the debris is still there, outside my kitchen window...

Noclevername
2014-Jul-13, 11:45 AM
after centuries, the building will be just debris, but its water will be removed forever from the cycle of rain, food etc...


Not forever, no. IIRC, concrete can eventually become subducted into the crust and those chemical bonds will be re-broken by heat, just as with hydrated minerals.