[Jim Colyer]

I thought Earth's atmosphere came from volcanos and that it rained for a million years to create the oceans.

My cousin told me, he heard on a science program that Earth's water came from meteorite impacts.

What is true?

[LJP07]

I always thought it came from huge meteorite impacts, and as far as I understand it's from two sources Primary Water and Water from Comets.

Two of the elements found in the Universe commonly are Oxygen and hydrogen. They are chemically quite reactive, and so they both combined with various other elements to form chemical compounds. One of these compounds is water, and water quickly became an important part of the earth's surficial layer ( Surficial Layer is the layer which is relating to something happening or being on earth), along with many other familiar chemicals like Silica. Water flowed and flowed which eventually became the oceans as we know it. However, in Earths First Billion years and over the past 4.5 billion years, the main source of water was from comets.

We know that comets consist chiefly of chemical compounds that are either gases or liquids at earth-surface conditions: methane is one common component of comets and water is another. Although I am not an expert in this field, that's how I currently understand it.

[hallenrm]

Here's a reliable link from where where you can get some useful information about your question. It is an article in wikipedia for the same topic.

[Turtle]

Originally Posted by Prolu2007

I always thought it came from huge meteorite impacts, and as far as I understand it's from two sources Primary Water and Water from Comets.

... However, in Earths First Billion years and over the past 4.5 billion years, the main source of water was from comets.

The water-from-comets idea is now passee.

Originally Posted by NASA

PASADENA -- A new Caltech study of comet Hale-Bopp suggests that comets did not give Earth its water, contrary to the longstanding belief of many planetary scientists.

http://www2.jpl.nasa.gov/comet/news98.html

Originally Posted by findarticle.com

Taken together with the signatures of volatiles on Earth, these data suggest that no more than 50 percent, and probably less than 15 percent, of Earth's water could have been added from space at the end of our planet's formation, says Drake.

http://www.findarticles.com/p/articl..._84546023/pg_1

[LJP07]

Originally Posted by Turtle

The water-from-comets idea is now passee.


http://www2.jpl.nasa.gov/comet/news98.html

They say in it's caption that it's probable that water didn't come from comets after all. There is proof of comet bombardment 4.5 billion years ago therefore, water must of came from them, maybe not all, but a significant amount. That first link said probable so I won't take it as fact.

[HydrogenBond]

What makes the most sense, is that the solar system stuff from which the sun and planets would form created its own density gradient, making the inside planets denser and the outer planets gaseous, with plenty of water, hydrated onto dust, concentrated where the earth would form. I am glad the comet theory for water was put to rest. Comets will also someday be put to rest with respect to the seeding of life. The earth had all it needed to get the job done, i.e, water and organics.

What is sort of interesting; if one placed a block of earth crust in a vessel and placed water on top, sealed it, and then heated it to the critical point of water, and then set up a thermal gradient, i.e, top cool and bottom hotter like the earth, the critical water will dissolve its way to the bottom, with the minerals in the crust crystallizing on top, even though the water has a lower density than the crust. A chemical potential drives the process. This is one way to make synthetic crystals like quartz and emeralds. If we reverse the thermal gradient (hot-top), the water would go up and crystals would form on the bottom. The earth has hot down instead of up. This earth design allows critical water to dissolve its way into the mantle replacing solids behind it.

One may ask, if water is in the mantle why do volcanos mostly have minerals and not too much water? The answer is simple, the water is displacing the minerals up.

[pmaust]

Originally Posted by Jim Colyer

I thought Earth's atmosphere came from volcanos and that it rained for a million years to create the oceans.

My cousin told me, he heard on a science program that Earth's water came from meteorite impacts.

What is true?

Many years ago, PBS aired a series called Miracle Planet. That series delt with the formation of the universe, solar system, and planets as I recall. Anyway, in one of the episodes, they demostrated how by adding heat to meteroite material water would begin to vaporize and then cool and condense into liquid form. The source water was trapped inside the meteorite material. It was postulated that as meteorites and other space stuff fell to the surface of the forming earth, the water was released due to the heat. Before there was sufficient gravity and atmosphere, the water vapor would simply return to space. Later, it began to get trapped in the forming atmosphere where later it condensed and rained down onto the earth surface.

The demonstration of releasing trapped water from space debris by the addition of heat sure made it appear like a plausible explanation.

[HydrogenBond]

One of the reasons water was speculated to come from comets, is comets are also needed to form the earth's supposed iron core. Without comets and because the earth is mostly oxygen as oxides, the iron core would have never phase separated from a starting cloud of ingredients. In other words, if one starts with iron plus oxygen one gets iron oxide. To form metallic iron one needs a reduction potential. Simple gravity will not separate out the iron, only iron oxide would settle in the core, not iron.

An abundance of hydrogen or carbon on the forming earth could provide this reduction potential but the amount of water or CO2 left on the earth should be much higher than observed, since the core is 10,000 times bigger than the oceans. The work around this practical constraint was to use comets to get the iron into the core very quickly before oxidation. The water became a bonus. Now the bonus is not considered correct. Comets for the core remains due to lack of challenging data. It is a theory needed to protect another theory.

Another conceptual problem with the comet theory is that the earth should not have been the only planet or moon formed by comets. There should be far more uniformity in all the rocky planets and their moons. All should have iron cores and all should have water. Venus has plenty of CO2 which is more volatile than water. I guess Venus was bombarded by specialty CO2 containing comets. To assume only the earth was in the path of a particular comet composition is absurd. It really came down to needing fresh absurdity to get politians to cough up resources. The hope was to slip it by common sense long enough to get resources, until data proves otherwise. This allows double the resources to disprove absurdity bringing us back to square one.

[Tormod]

Well, the comet theory isn't entirely dead. The Deep Impact project last summer proved that comets can contain immense amounts of water. It spouted water for days after the impact.

There was also (to the scientists' surprise) water ice on the surface:

http://www.nasa.gov/mission_pages/de...water_ice.html

A chief scientist said (early this year):

Originally Posted by Chief Scientist

"Understanding a comet’s water cycle and supply is critical to understanding these bodies as a system and as a possible source that delivered water to Earth," she said. "Add the large organic component in comets and you have two of the key ingredients for life."

Which shows that the water-from-comets idea is far from passe, nor is the life-from-comets idea dead.

Edit: The "death-from-comets" theory is still alive, too.

I do agree with HydrogenBond that life may well have come about on Earth without the help of matter from comets. Some have speculated that comet impacts may have caused impact fragments to blast into space and carry life between the planets (ie, we could all be Martians ).

[ezguine]

Hello, a response to a very old post.
I believe that earth's water is the ashes of a former atmosphere consisting mostly of hydrogen which at some point was ignited and the whole atmosphere flashed into flame. The resulting compound from the chemical reaction is today's water. Just thought I'd throw my late opinion out there after coming across this post on Google