Origin of water on the earth?

[bdewoody]

I watched a program over the weekend speculating on the source of all the water we now have on earth and I went awawy more confused than before. Long held theory was the source was comets, but after inspecting water from only one comet (Haley) they have ruled out that source. Something about the ratio of heavy hydrogen atoms in the water molecules not matching. Then they proposed the water was here all along, condensing on the rubble that eventually formed the earth, but again inspection of water contained in metorites suggested that the hydrogen ratio didn't match. So then they went on to propose the collision with the object that created the moon might be the source. My question is why can't it be a mix of all the theories? And why are they spending so much money to find out anyway?

 

[UFmbutler]

And why are they spending so much money to find out anyway?

Because if we can determine which mechanism is primarily responsible, we can then estimate the likelihood of water being present on other planets outside of the solar system similar to Earth. It's unclear how big of a difference in the probability there would be between say, the comet mechanism and the large collision mechanism, but it is a significant part in figuring out how likely life has formed on other planets.

 

[ZenGalacticore]

I saw the same program, and it was damn interesting!

The gist is that the water in comets is too heavy-ie, too much heavy hydrogen in ratio to O atoms.

We now speculate that most of the familiar H20 molecule-water on Earth was captured in the aggregation of the Earth from the get-go.*

Don't you just love it when old theories are shattered!! Or at least viably questioned and challenged?

More interesting still because we have known about "Heavy Water" for a while now.

 

[greddytalon]

I don't see how it could have been here all along. When Earth was a fireball, there was no atmosphere that could have allowed for condensation...so my guess is also the moon forming event. It is very interesting indeed though!

 

[ZenGalacticore]

Maybe the water was captured inside the aggregating Earth at different phases of its formation. Later on, as the planet began to cool-relative to its former temperatures- the water vapor escaped via volcanic activity.

Digesting all that I've read about Earth's formation over the years, the gist is that that first 400 or 500 million years or so was a very to-and-fro, back-and-forth, complicated process. It would start to cool off, perhaps condensation would form and it would begin to rain in places, then another object would strike in the 'busy' early solar system, and the planet would heat up and start boiling frenetically all over again.

 

[aphh]

Water is a molecule, remember? 2H2 + O2 = 2H2O. So water didn't exist, it was formed in a bang, where hydrogen atoms collided with oxygen atoms violently.

You put hydrogen and oxygen in the same space and give them a spark, you have instant water (and a very big bang too).

My theory is there was sufficient amount of both elements in the athmosphere of the early earth. Lightning strikes provided the spark and water was created. When water was created, this helped cool down the athmosphere and Earth over time.

What if comets only brought either hydrogen or oxygen, other element being here already, and water was formed in the collision?