Earth's water: where did it come from?

PlutonianEmpire · Post #1by **PlutonianEmpire** » 21.10.2007, 22:21

A few weeks ago I saw on the history channel a special, "how the earth was made", and IIRC, it mentioned the formation of our oceans, and made me think of the question. how did earth go from a dry rock world to one with ovedr 70% ocean?

maybe it came from that one body that crashed into earth and created the moon?

then of course, how did THAT body get enough water to give us water vapor?

Hungry4info · Post #2by **Hungry4info** » 21.10.2007, 23:42

Comets delivered water I believe. The water originated from the outer solar system.

MKruer · Post #3by **MKruer** » 21.10.2007, 23:57

I think you are confusing area with mass. Though the earth surface is covered by 70% water, water only accounts for a fraction of the earths over all mass.

"The mass of the oceans is approximately 1.35?—1018 metric tons, or about 1/4400 of the total mass of the Earth, and occupies a volume of 1.386?—109 km??." http://en.wikipedia.org/wiki/Earth

On top of that, water is not that hard to make considering the a systems composition. Namely Hydrogen and Oxygen. H2O, two very abundant elements generated is stars.

This might interest you as well.
http://space.newscientist.com/article/d ... space.html

ajtribick · Post #4by **ajtribick** » 22.10.2007, 16:29

An interesting question related to this is how much water is contained within the Earth: there might be fairly large amounts in the mantle (possible example is the Beijing anomaly)

BobHegwood · Post #5by **BobHegwood** » 22.10.2007, 21:16

Hungry4info wrote:Comets delivered water I believe. The water originated from the outer solar system.

You know, I keep hearing that on the Science Channel and other places,
but I have trouble believing it.

Wouldn't there have to have been either an ENORMOUS number of comets
hitting the Earth in the past, or a few VERY large ones to do this trick?

Confused - as usual - Brain-Dead Bob

Post #6by **selden** » 22.10.2007, 21:36

Enormous numbers. And big ones.

Look at what they did to the Moon!

BobHegwood · Post #7by **BobHegwood** » 22.10.2007, 21:47

selden wrote:Enormous numbers. And big ones.

Look at what they did to the Moon!

Comets? Asteroids I can understand, but Comets? Don't know why I
thought this, but I thought that comets were in far fewer supply than
asteroids. This is incorrect?

Thanks Teacher. I'll leave you alone for a while now, I PROMISE...

Post #8by **selden** » 22.10.2007, 22:01

fewer does not mean few.

Presumably most of the damage still visible on the Moon was indeed done by protoplanetary bodies similar to what we now label asteroids of various sizes, but there would have been lots of protoplanets with high water content, too.

tony873004 · Post #9by **tony873004** » 23.10.2007, 00:24

I believe the problem with comets is that the water has the wrong isoptotes: too much heavy water. Asteroids would be more likely.

Hungry4info · Post #10by **Hungry4info** » 23.10.2007, 13:27

There is heavy water in our oceans, though in low concentrations. Also, there may not seem to be many comets now, making the idea that comets delivered water to the planets seem unlikely. But remember, the early solar system had a lot more comets. Since then, many have impacted planets, and the impact rate goes down over time. Indeed, comet impacts still occur these days (SL9).

BobHegwood · Post #11by **BobHegwood** » 23.10.2007, 14:41

Hungry4info wrote:Also, there may not seem to be many comets now, making the idea that comets delivered water to the planets seem unlikely. But remember, the early solar system had a lot more comets. Since then, many have impacted planets, and the impact rate goes down over time. Indeed, comet impacts still occur these days (SL9).

No kidding...

Believe me, I understand everything you're telling me here, but your
explanation of "the early solar system had a lot more comets" makes no
sense to me. I'm certain that the early solar system had a LOT more
asteroids too, but you can still go outside almost any night and see small
asteroids entering the Earth's atmosphere. In fact, I saw one three
nights ago over my home in Germantown, Ohio.

Sorry, I don't really know WHY this explanation bothers me, but it does.
Feel free to hit me over the head with your baseball bat anytime you
like. :lol:

Fenerit · Post #12by **Fenerit** » 23.10.2007, 14:45

Just a thought: if the protostellar matter follow in part all the stellar element-burning phases, during the planets condensation the excess of H2 will escape from the rest of the elements, mixing itself with the O2 layer. In this frame I do not believe that the presence of water has been a rapid process; rather it may be a slowest process, according with the cooling of the planet. For Mercury and Venus the H was in excess over the O2 whereas for Mars the contrary: was the O2 in excess over the H. For the first nothing rest of both (just the H2), for the second the result is a generalized so-called "greenhouse effect" and for the third the red color.

Post #13by **selden** » 23.10.2007, 14:59

Bob,

If you don't understand why it bothers you, I don't think we can help make it not bother you.

Maybe it would help if you read some of the papers written about the current theories of planetary formation.

Like maybe this one:

arXiv:0706.1239 [ps, pdf, other]
Title: Water vapour and hydrogen in the terrestrial-planet-forming region of a protoplanetary disk
Authors: J.A. Eisner

http://arxiv.org/abs/0706.1239

BobHegwood · Post #14by **BobHegwood** » 23.10.2007, 15:10

selden wrote:Bob,

Maybe it would help if you read some of the papers written about the current theories of planetary formation.

Oh Hell... There you go being logical again. Thanks Selden. Will go look
as soon as I get everything else on this new PC working correctly.

Take care, Bob

BobHegwood · Post #15by **BobHegwood** » 26.10.2007, 13:32

The ONLY thing I understood about that paper was:

"The observed water vapor is likely produced by the sublimation of
migrating icy bodies, and provides a potential reservoir of water for
terrestrial planets."

However, this paper supports the conclusion that comets accounted for all
of the Earth's water not at all...

Certainly they may account for SOME of the water, and I don't have any
problem with that. Its just that the Earth's VOLUME of water staggers the
imagination when you think about it. In my opinion, either a VERY large
series of comets brought the water to Earth, or - more likely - the water
came about as a by-product of the hydrogen and oxygen in Earth's early
life coming together somehow.

I KNOW I'm gonna catch hell for saying these things since I don't know
BEANS about the scientific theories - or terminology - but that's what I
think. So there...

Thanks, Brain-Dead

Fenerit · Post #16by **Fenerit** » 26.10.2007, 15:23

There is more, Bob. My skepticism about the icy comets hits is similar as the your, since it's as "to explain the unknow with the more unknow" (my quick traslation of Galileo's words, I apologize for the uncorrectness of the translation in terms of English language); that is: it's not completly sure how the comets also become and/or hold the ice during the early stage of the SS!

BobHegwood · Post #17by **BobHegwood** » 26.10.2007, 21:18

Well, thanks for NOT yelling at me anyway. <grin> I'm certain that
someone will fulfill my expectations here shortly though. Hee, hee.

I know I'm not a scientist, but I do like to understand things, and I'm afraid
that all the official explanations make no sense to me so far. <shrug>

Take care, Bob

MKruer · Post #18by **MKruer** » 26.10.2007, 22:47

Bob,

Think of it this way,

Go out side and pick up a rock, a typical rock will contain about 0.1% water. All the oceans on the planet only account for 1/4400 the mass or 0.000227% of the mass.
Through the process of planet forming, chemical and thermal exchanges converted the raw elements into water. It was literally pulled out of the rocks. This does not limited the chance that comets brought some water to the planet, but still the bulk of water is terrestrial in origin not extraterrestrial.

BobHegwood · Post #19by **BobHegwood** » 26.10.2007, 23:26

MKruer wrote:Bob,

Think of it this way,

Go out side and pick up a rock, a typical rock will contain about 0.1% water. All the oceans on the planet only account for 1/4400 the mass or 0.000227% of the mass.
Through the process of planet forming, chemical and thermal exchanges converted the raw elements into water. It was literally pulled out of the rocks. This does not limited the chance that comets brought some water to the planet, but still the bulk of water is terrestrial in origin not extraterrestrial.

Well, THAT at least makes some sense to me... Thanks VERY much for the
understandable explanation. See? I'm not hard to please. Your line of
thinking agrees with my instincts - whatever THAT means.

Can we hear from the other side now? I'd REALLY like to know why
scientists (at least the bulk of them) keep insisting that the Earth's
oceans came from comets...

Thanks, Bob

MKruer · Post #20by **MKruer** » 27.10.2007, 00:36

Bob

You might be interested in this; particularity the Hadean period.

http://en.wikipedia.org/wiki/Geologic_time_scale
http://en.wikipedia.org/wiki/Hadean
http://en.wikipedia.org/wiki/Abundance_ ... l_elements

My main problem with the extraterrestrial origin of water is that where did it (the extraterrestrial water/ice) come from? Water is two Hydrogen and Oxygen elements that form H2O. Both elements are widely available in the interstellar medium (space). On a percentage basis, based upon element in the universe the Earth should have many times the amount of water then it does but it doesn?€™t. By mass, Earth would be 60% water.

So in my not so humble opinion the question should not be ?€?where did water come from??€