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Fraser
2004-Jun-16, 04:48 PM
SUMMARY: Where did the world's oceans come from? Some scientists believe all that water was originally locked into rocks, and slowly leaked out over millions of years. Others believe it was delivered from space by comets crashing into our planet. The European Space Agency's Rosetta spacecraft might help find the answer. When it reaches Comet 67P/Churyumov-Gerasimenko, Rosetta will send down a small lander, Ptolemy, that will measure the chemical signature of the comet's water, and see if that matches our water.

What do you think about this story? Post your comments below.

damienpaul
2004-Jun-16, 05:03 PM
Now this will be exciting. I wonder if they can detect amino acids or organic compounds.

StarLab
2004-Jun-16, 05:32 PM
While water from comets is being speculated, meanwhile, the idea that water came from rocks, to me, is bogus. if water came from rocks, rocks would still be pouring water. Though I am no expert in ancient history rockology, I find it amusing rockologists and geologists would believe or even put forth for that matter that rocks dished out water a long time ago and then stopped. I can tell you right now that knowing some stuff about rocks, I'd guess that if rocks did indeed splurt out water in the archaeozoic, they'd still be doin' it today.

antoniseb
2004-Jun-16, 08:01 PM
I'm not sure that comets that hit the earth during the bombardment period were the same as the ones flying around now. They've had quite a bit of time for their more volatile molecules to be driven off, and their outer molecules to be corrupted by solar radiation.

Also, if comets brough water, where's the water on venus? Certainly there is not the same amount in its atmosphere as we have in our oceans.

damienpaul
2004-Jun-16, 08:07 PM
mixed with sulphur dioxide to produce the sulphuric acid atmosphere perhaps

StarLab
2004-Jun-16, 08:29 PM
Well, how is it that if earth, mars, and venus all've had atmospheres, even though all three are different, why is ours the one with life, and why is there a different in chemical atmospheric content, in the first place?

TuTone
2004-Jun-16, 08:51 PM
Water didn't come from rocks. That's a dumb theory. ;)

rocket
2004-Jun-17, 12:09 AM
Dear Universe Today,
For "where did the earth's water come from?" I think that there was something, perhaps anamino acid, or some other element in the soup that caused the hydrogen and onxygen to combine. This made it heavier so it sank to the surface, then reached a kind of balance, an equilibrium whereby the same amount is kept in a status quo.

Algenon the mouse
2004-Jun-17, 12:55 AM
From what I understand, even though it may seem like the earth is the only planet in the solar system with water, it isn't. New speculations have said that Mars may have more water than earth. It is just frozen. Several moons have water as well. It is possible that the water was brought to earth by a comet or it could have been there all along.

Greg
2004-Jun-17, 02:20 AM
Do not forget the implications of the dominant geologic process on our planet. Plate tectonics is driven by water, believe it or not. Water erodes the continents dumping soil via rivers on the continental shelfs. Once the shelfs become laden enough, they literally sink through the crust into the mantle. This is how subduction zones are now thought to be formed. Oceanic ridges are the other half of the story and are thought to be interrelated to the effects of the subduction zones in the mantle.
One fundamental puzzle regarding plate tectonic theory has been that the subduction process takes a huge volume of water into the mantle at a constant rate. Volcanoes associated with subduction zones like the Cascades recycle some of the water but only a small fraction back into the atmosphere. At the rate water is being drawn into the mantle, our oceans should have dried up at least a billion years ago. Once that happened plate tectonics would stop and massive volcanic eruptions would follow akin to what happened in Mars, the moon and Venus, probably causing a runaway greenhouse effect like what now exists on Venus.
So how has Earth been replenishing its water? There was a satellite study a few years back that looked for the signature of microcomets burning up in our atmosphere and found them in abundance. Enough microcomet hits were seen that would deliver enough water to replenish our oceans every billion years or so. The study was heralded by a news magazine which is how I found it, but I would have a devil of a time locating it several years later. So based on this knowledge, I would predict that the probe will find that the comet H2O has the same isotope ratios as what we have here on Earth.

Tinaa
2004-Jun-17, 12:52 PM
Io is a rocky world. And where did he idea come from that Jupiter had babies?

1. We don't even know if the Jovian planets do have rocky cores.

2. Earth has been in approx. the same orbit for billions of years. No planet X.

3. So what? Just because the animals lived in the water doesn't mean there was no land. No planet X to make us turn over and spill our water.

4. Wrong. Again, no planet X. Mars is not massive enough to keep a dense atmosphere. No hot spinning core, no protective magnetosphere. No protective magnetosphere, lots of radiation. Lots of radiation probably caused any surface water to break into seperate H and O. H escaped into space and O was bound up in the rocks. Or maybe there is still lots of water under the surface of Mars.

5. Who knows? Earth will probably be incinerated when the sun expands into the Red Giant phase.

Stop with the planet X nonsense.

GOURDHEAD
2004-Jun-17, 02:04 PM
Some scientists believe all that water was originally locked into rocks, and slowly leaked out over millions of years. Others believe it was delivered from space by comets crashing into our planet.

My guess is that both rocks and comets have contributed. Back when the earth was beginning to be accreted from the dust, water, and rocks in the protoplanetary cloud (or disk) water ice may have been a great catalyst for glueing the stuff together. Many varieties of minerals (rocks) arrive (or become) in hydrated forms with chemical formulas of the form ".17H2O" (17 is an arbitrary placeholder for variable numbers depending on the degree of hydration). As pressure and temperature increase from the earth growing in size, the rocks lose or decrease their hydration becoming a source for oceanic water. Meanwhile comets add water continually more than replacing that lost to the disassociation of water into H and O in the upper atmosphere.

The reason the rocks don't continue to gush forth (aside from geothermal events), their level of hydration is essentially in equilibrium.

Whatever is the case, the ultimate source for most of the water in earth's oceans came from the material in the primordial solar system as did that remaining aloft in comets. I wouldn't expect isotopic ratio differences. Why do they?

Tannhaeuser
2004-Jun-17, 10:20 PM
Originally posted by antoniseb@Jun 16 2004, 08:01 PM
where's the water on venus?
Quite simple, because of the heat on venus, all water became steam, and because H2O is a rather light molecule in comparison to N2 or CO2, it simply boiled off into space. Even Comets who strike Venus don't even hit the ground, because they boil off before.
or in popular language: Lady Venus is too hot a babe to get wet ;)

j boy
2005-Aug-11, 09:41 PM
dood there is no way that the way the water in the earthwas "excreted" by rocks I mean its ilogical look at how hard they are.

Duane
2005-Aug-11, 10:11 PM
Actually boys and girls, there is every possibility that the rocks which came to form the Earth were heavily hydrated, although I have no doubt that coments also contributed to the amount of the water in Earths oceans.

Greg, you have a couple of misconceptions. While water is important to plate tectonics, the driving force behind them is the melted, circulating mantle. The continental roots extend into the mantle to a depth of about 600 miles (or KM, but I think it's miles) and they get carried along as the mantle circulates. Well, more precisely, they are pushed along with the ocean floor as the mantle wells up in mid-ocean ridges and the ocean floor expands.

One area where you can see this happening on dry land is the Great Rift Valley in Africa. This is a zone of upwelling that is slowly pushing the eastern part of Africa away from the western part.

Hydration is important in helping the lubricate the subduction of the ocean floor where it meets the lighter continental shelf, or where two plates meet. That is not to say that there are not areas where subduction doen't need water--the collision between the Asian and Indian plates attests to this.

Finally, there is a heavily hydrated layer in the lower mantle, off the top of my head I think it's 600 to 900 miles beneath the surface. At this level, the temperature of the mantle is high enough to liberate the hydration in the sinking lithospheric plate.

The idea of micro-comets is pretty contencious (sp?) right now. There is very little evidence to support the idea, although the idea is being studied pretty closely.

Svemir
2005-Aug-12, 06:45 AM
Originally posted by Tannhaeuser+Jun 17 2004, 10:20 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Tannhaeuser &#064; Jun 17 2004, 10:20 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-antoniseb@Jun 16 2004, 08:01 PM
where&#39;s the water on venus?
Quite simple, because of the heat on Venus, all water became steam, and because H2O is a rather light molecule in comparison to N2 or CO2, it simply boiled off into space. Even Comets who strike Venus don&#39;t even hit the ground, because they boil off before.
or in popular language: Lady Venus is too hot a babe to get wet ;) [/b][/quote]
But Mercury has ice caps, where it&#39;s water comes from ?
Comets that strikes the Earth evaporate too, specially "microcomets" or any other "micro" stuff. That&#39;s beacuse they hit an atmosphere not because the planet is hot.
We don&#39;t know much of Venus and it&#39;s atmosphere, but I suppose some of the Venus water is bound in H(2)SO(4) [or as dissociated ions water and sulfur dioxide]
Anyway, if we connect several "findings" i.e. microcomets hitting the Earth (and Venus) in an amount enaugh for Earth to replenish it&#39;s water, we should find a water layer on Venus in the upper atmosphere.
Water steam does not go into the space just like that.
(Neither does Ozone layer on Earth ).
If replenishing mechanism (microcomets) is enough for Earth to replenish it&#39;s water then it should be more then enough for Venus to do the same.
And how does this fit with the newest one that Mars has been dry for quite some time?
Why microcomets didn&#39;t bring more water to Mars?

And what about Jupiter? Shouldn&#39;t it be the planet with water in aboundance (if water comes from space) in the upper atmosphere? Or at least dissociated water.

I amused myself with some calculations based on NASA data that Earth recieves about 50.000 tons of material from space each day.
I came to conclusion that Earth raughly gained 1 millionth part of it&#39;s mas (and hence gravity) from the era of dinosaurus (65 mill. years).That&#39;s not enough to explain supposedly lower gravity in the dino-era
(that&#39;s what I was investigating :-)) and the amount of water on Earth even if all of the infalling material was water (it isn&#39;t).
Another thing is that comets don&#39;t possess so much water as previously thaught.

cran
2005-Aug-12, 08:17 AM
:) Some interesting viewpoints put forward so far ... and some reasonable corrections to not uncommon misconceptions ... perhaps I can put the original question into context?

The solar sytem is thought to have formed at more or less the same time, from a turbulent, collapsing, and rotating mess of stuff... with ratios of material approximately equal to solar abundances (and modified for solar nuclear synthesis for the interim), so it was thought to be mainly hydrogen, with lesser amounts of other elements, compounds, and minerals ... including water and silicates.

planetary formation includes the process of accretion, where gravity assists the concentration of matter ... the more mass a protoplanet has, the faster it can attract more material ... including water and silicates ... and yes, many minerals found (even in meteorites) are hydrated minerals (though not always in the form H2O, more commonly it is just OH -which, if liberated, will readily bond with a free hydrogen to form H2O - often the process is 4(OH) => 2(H2O2) => 2(H2O)+2(O); the oxygen is then readily snapped up, by another oxygen, if there is nothing else.

during the process of accretion, larger accreting bodies will also undergo another process called differentiation, where material will reorganise into layers according to relative densities ... it is by definition a &#39;fluid&#39; process ...

both accretion and differentiation continue today on Earth, though at very very reduced rates compared with the early stages of planetary formation ... so, the Earth does indeed continue to accumulate material (including water and silicates) from beyond the atmosphere ... and no, the Earth is not in equilibrium yet, and differentiation is still continuing ... and yes, water is still being liberated from rocks (it&#39;s not gushing now...if it ever was, but it is happening)

about 3.9 billion years ago (about 2 galactic revolutions, assuming near constant rate, after the planetary accretion phase had begun), the Earth and Moon were subject to a level of bombardment of mostly cometary material, possibly from the same source as the initial solar system material...

The Question is whether that cometary bombardment provided the bulk of water required for the first oceans ... the ancilliary questions are:

1) Was there significant surface, near surface, and atmospheric water on Earth prior to the bombardment? (ie, were there oceans or seas before the comets came?) - the answer in the geological record is "YES"

2) Did the 3.9 GA BP bombardment strip away the primitive atmosphere and surface water, and replace it? - the answer in the geological record is "Don&#39;t know"
...but my own thinking is &#39;no, but it did contribute to what was already here&#39;.

Oh, and rifts and mid ocean ridges don&#39;t rise up because of magma forcing it; they rise up because of density differences (reduced density gradients due to increased thermal gradients), the hot magma fills the spaces created because it is less dense still... erupting magma doesn&#39;t have enough force to &#39;push&#39; plates apart ... if it did we would see &#39;crumple zones&#39; along spreading ridges, the same as we find them at convergent plate margins ... plate movements (including at subduction zones) are more assisted by &#39;mantle cell drag&#39; - most of the water that is carried down into a subduction zone acts as a catalyst to reduce the melting point of the marginal mantle - leading to andesitic magmas (with lots of steam) that form large explosive volcanic chains (think Mt St Helens, Vesuvius, Pele) and underplate the granitic continental mass... I don&#39;t know where the idea that all of the oceans would have flowed into subduction zones came from? Is there a source for that idea?

The bits about water on Venus? Yes, some seems to be tied up in sulfuric acid, but a lot is unaccounted for...did it boil away into space? possibly, but not so much in the manner suggested ... water is a reasonably massive molecule, and Venus has the mass to retain it, regardless of the temperature ... however, water can be fairly easily dissociated into hydrogen and oxygen and the hydrogen is certainly light enough to escape into space; the oxygen can be captured by carbon monoxide (CO) to form carbon dioxide (CO2), which just happens to be the most abundant constituent of the Venusian atmosphere... :)

cran
2005-Aug-12, 08:32 AM
(reduced density gradients due to increased thermal gradients)
:blink: Sorry, I meant &#39;increased density gradients due to&#39; etc which means that the density of the overlying crust is reduced (and therefore rises) because it is hotter than the surrounding rock - this is most noticable in the mid-ocean ridges because the crust is thinner leading to much higher thermal gradients (change in temperature (or heat flux) with increasing depth below surface.

cran
2005-Aug-12, 08:34 AM
The solar sytem is thought to :huh:

&#39;system&#39;&#33; system&#33;

I&#39;m gonna fire my proof-reader&#33; :angry:

Jakenorrish
2005-Aug-12, 02:19 PM
Well, how is it that if earth, mars, and venus all&#39;ve had atmospheres, even though all three are different, why is ours the one with life, and why is there a different in chemical atmospheric content, in the first place?

Well, we can probably say that life on Venus is unlikely, but there may be life on Mars so don&#39;t discount it yet&#33;

cran
2005-Aug-12, 09:35 PM
We can link the Earth&#39;s rather unique atmospheric chemical evolution to two key factors: the internal dynamo that generates a strong magnetic field; and the emergence and evolution of life ... without the first, most of the Earth&#39;s surface water may have been dissociated and most of the hydrogen lost to space; without the second, CO2 would have been the most abundant constituent; without both, the Earth would be like Venus, but with an even denser atmosphere ... :o

It&#39;s thought that the internal dynamo in Mars shut down because its higher mass/surface ratio means a higher heat loss from the interior - ie, it was too small to retain enough heat for enough time ... :ph34r:

Why Venus doesn&#39;t have a comparable internal dynamo is still being debated; but my money is on Venus&#39; lack of the third unique feature that we have - a substantial moon.
:)

Duane
2005-Aug-12, 09:55 PM
Oh, and rifts and mid ocean ridges don&#39;t rise up because of magma forcing it; they rise up because of density differences (reduced density gradients due to increased thermal gradients), the hot magma fills the spaces created because it is less dense still... erupting magma doesn&#39;t have enough force to &#39;push&#39; plates apart ...

Well, partly true. The mid-ocean ridges are zones of divergent (spreading) plates. As the plates spread apart, magma wells up to fill the gap. The plates are thought to follow convection currents in the upper mantle.


I&#39;m gonna fire my proof-reader&#33;

Hahaha I think we use the same one&#33;&#33;&#33;

Duane
2005-Aug-12, 10:02 PM
Originally posted by cran@Aug 12 2005, 02:35 PM
Why Venus doesn&#39;t have a comparable internal dynamo is still being debated; but my money is on Venus&#39; lack of the third unique feature that we have - a substantial moon.
:)
There is also the theory that Venus will occasionally undergo a planet wide eruption event every 500,000 yrs or so. The internal heat is there, and studies of volcanos on Venus also seem to identify hotspots similar to Hawaii or Yellowstone on Earth. Why no magnetic field? There is the &#036;64,000 question.

cran
2005-Aug-12, 10:24 PM
There is also the theory that Venus will occasionally undergo a planet wide eruption event every 500,000 yrs or so. The internal heat is there, and studies of volcanos on Venus also seem to identify hotspots similar to Hawaii or Yellowstone on Earth. Why no magnetic field? There is the &#036;64,000 question.
you&#39;re right, Duane ... the global resurfacing seems to be a response to the lack of substantial surface and subsurface water to facilitate &#39;normal&#39; plate tectonics ... or it might be that one of the major impact events on Earth coincided with a bigger impact event on Venus, and that poor planet is still reeling from it... but I&#39;m favouring the former :)

And I&#39;ve already given my view on the &#036;64000 question - no moon&#33; :)


The plates are thought to follow convection currents in the upper mantle. Yes, what did I call it? &#39;mantle cell drag&#39; - it is the adiabatic component of the convection cell - called &#39;advection&#39; - it is accompanied by &#39;adduction&#39; (advective conduction) - heat transfer to the crust - the downward component is &#39;density-driven flow&#39; because the cooled magma is denser than its surroundings...

Duane
2005-Aug-12, 11:03 PM
Ah, ok I see where you&#39;re going with that now. Yep, that about says it&#33;&#33;

cran
2005-Aug-12, 11:54 PM
thank you, Duane... >blush< :)

When I worked in politics, our motto was &#39;it doesn&#39;t matter who gets the credit, as long as it happens&#39;

I hope someone makes a definitive answer to all of these questions... happen B)

But then, we&#39;d have to find new questions... <_<

Svemir
2005-Aug-16, 05:48 AM
This paper Water in a protoplanetary disc (http://www.arxiv.org/PS_cache/astro-ph/pdf/0508/0508256.pdf) is connected to our issue but it&#39;s IMO one of the most important in the recent times, mainly because of it&#39;s precision and clearness.

Duane
2005-Aug-16, 06:50 PM
That was an excellent paper svemir&#33;

cran
2005-Aug-16, 10:50 PM
Duane, or Svemir?

Can you provide a full reference to the paper - my old computer refuses to open PDF documents these days :angry: , but with a reference I can track down an html or hard copy version somewhere...

please? :)

or... just summarise the abstract and conclusions? :)

Hermes
2005-Aug-16, 11:09 PM
You cannot squeeze water from a stone - ANON

cran
2005-Aug-16, 11:14 PM
Sorry, ANON, but you can... nature, and geoscience labs do it all the time. :)

Svemir
2005-Aug-17, 05:46 AM
"Discovery of deuterated water in a young proto-planetary disk"
C. Ceccarelli, C. Dominik, E. Caux, B. Lefloch, P. Caselli
11.08.2005

cran
2005-Aug-17, 07:34 AM
Svemir, you&#39;re a champion&#33; :D
Thank you...