The Naked Scientists

The Naked Scientists Forum

Author Topic: Is Earth losing water?  (Read 3562 times)

Offline colarris

  • Full Member
  • ***
  • Posts: 54
    • View Profile
Is Earth losing water?
« on: 02/10/2013 21:11:16 »
Is the Earth losing it's water? Has it the same amount as when the seas first formed or is it very slowly disappearing, if possible(?)
« Last Edit: 04/10/2013 18:20:10 by chris »


 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: Unlimited water?
« Reply #1 on: 02/10/2013 22:25:05 »
It is possible that some water has been "lost". 

When life produced oxygen for the atmosphere, starting about 2.4 billion years ago, with great increases in the last billion years, that would have necessarily decreased some of the water.

n(CO2 + H2O) ==> (CH2)n + n(3/2)O2  (roughly estimating the large variety of hydrocarbons possible).

So, the formation of hydrocarbons requires water.

I'm seeing estimates of about 2 x 1015 tons of oxygen in the atmosphere.  About 1/3 of that would have come from water, so somewhere around 7 x 1014 tons of water would have been converted into oxygen.

A small amount of free hydrogen may also leak from the earth, although this may be replenished by the solar wind and cosmic rays.

Some additional water may come from comets, comet fragments, and icy bodies impacting the Earth.
 

Offline colarris

  • Full Member
  • ***
  • Posts: 54
    • View Profile
Re: Unlimited water?
« Reply #2 on: 03/10/2013 11:18:22 »
Many thanks for the detailed answer. :)
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: Unlimited water?
« Reply #3 on: 03/10/2013 12:24:02 »
I suppose another thing to think about is the molecular weight of water is:
H: 1
N: 14
O: 16

H2O: 18
N2: 28
O2: 32

That means that in its molecular vapor form, water is lighter than air.

Fortunately our lower atmosphere, or troposphere gets cooler as one goes up, and the top of the troposphere is very cold, about -50C (plus or minus a bit).  This freezes most of the water in the upper atmosphere and it falls back to Earth. 

I did find an article suggesting that some water does make it into the stratosphere.  The temperature in the stratosphere increases somewhat so any high altitude water might actually be in vapor form making it difficult for it to return to Earth.  Still, there doesn't seem to be a lot of water vapor escaping the atmosphere.

Ocean water levels of course also vary significantly based on the amount of ice on Antarctica and Greenland, and other land masses.  Sea Ice, however, doesn't greatly affect the sea level.  It is believed that Antarctic has generally been ice free a few times during Earth's history.
 

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1879
  • Thanked: 144 times
    • View Profile
Re: Unlimited water?
« Reply #4 on: 03/10/2013 21:34:50 »
I suspect a geologist would know better, but I think it more likely that water could react with with metals or minerals in the crust (and below?) than for it to escape into space. Most of the stiff in the crust is highly oxidized (O is most abundant element by mass in crust). However, there is much less oxygen deeper down in the earth, and in fact very deep down is mostly reduced metals! I don't know to what extent there is mixing, but I feel like if any water gets subducted, it is likely to react with whatever is down there.

Of course at high temperatures it can be thermodynamically favorable to lose water or oxygen from minerals to form metals or very dry oxides, so it could be that the water at the surface is in equilibrium with that above and below, and until the earth cools down a lot more our water should remain pretty constant.
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: Unlimited water?
« Reply #5 on: 03/10/2013 21:54:49 »
I thought that water was acting as a catalyst rather than a reactant in the oxidization of iron (and other minerals).  Water does go quite deep, and is often brackish when found deep.  However, does deep water lack free oxygen?

Could life have affected the oxidation state of minerals in the crust, especially in deep layers which might have existed prior to the great oxidation event?
 

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1879
  • Thanked: 144 times
    • View Profile
Re: Is Earth losing water?
« Reply #6 on: 05/10/2013 18:50:45 »
With plenty of oxygen around, water acts as a catalyst. But even without any oxygen, water is capable of oxidizing iron (at elevated temperatures), releasing hydrogen in the process (H2O + Fe --> FeO + H2). If the H2 is somehow able to escape into the atmosphere, I imagine much of it would eventually end up in space. (but most of the mass of the water lost would still be on earth, as oxygen accounts for almost 90% of the mass in water)
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: Is Earth losing water?
« Reply #7 on: 05/10/2013 21:22:52 »
At elevated temperatures, hydrocarbons will also reduce iron, and other metals.

Fe2O3 + Hydrocarbons ==> Fe + CO2 + Water    (not balanced)
 

Offline Pmb

  • Neilep Level Member
  • ******
  • Posts: 1838
  • Physicist
    • View Profile
    • New England Science Constortium
Re: Is Earth losing water?
« Reply #8 on: 07/10/2013 01:31:16 »
Questions like this are very hard to answer. It is thought that the water on earth came from comets. Since this process has all but stopped its likely that there is no increase in the amount of water. Other changes responsible for the amount of water on earth are chemical processes, including biochemical processes. It seems to me that any changes become magnified over billions of years so there must be an over all balance where sometimes it increases and other times decreases while all the time trying to maintain a stasis level.
 

The Naked Scientists Forum

Re: Is Earth losing water?
« Reply #8 on: 07/10/2013 01:31:16 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums