I clearly remember my high school science teachers telling me that water vapor is a by-product of all sorts of chemical reactions, yet when I watch The Science Channel and The Discovery Channel do shows about the history of the earth, they always say the earth’s water came from comets.
Why is it that comets are the source of our water and not the quintillions and quintillions (and quintillions) of chemical reactions over the last 4.5 billion years?
1st Law of Thermodynamics
and I believe the OP should read “Don’t drink water, fish fuck in it.”
Yes! they not only poop in it, they fuck in it too. That is why the ocean tastes salty. Well, there are other reasons involving rocks and rain.
That’s one theory. It’s probably the most likely, but I don’t think it has been proven yet.
So here’s the deal. If you look at the outer solar system, there are a bizillion little ice balls out there, some bigger than others. So it’s likely that ice balls and other types of space dust all collapsed together due to gravity and formed the Earth.
But here is where it gets complicated. Fairly early in the formation of the solar system, something roughly the size of mars slammed into the Earth. Needless to say, this wasn’t a happy time for the Earth. The end result of this collision was that whatever crust had been forming on the surface of the Earth was completely obliterated, and a bunch of stuff thrown into orbit around the Earth that eventually formed the moon.
And this gets us to the big question. Did the Earth manage to hang on to all of that water that it had during its formation, or was most of it blasted into space during this collision? If the Earth managed to hang on to its water, then most of it didn’t come from little ice balls like comets slamming into the Earth. But if most of the water got blasted into space, then the water did have to come from little comet ice balls. Otherwise, we wouldn’t have any water.
If you look at ice balls throughout the solar system, there is a fairly common ratio of normal water and “heavy” water (deuterium, a heavy isotope of hydrogen since it has both a proton and a neutron, combined with oxygen). Since heavy water is, well, heavier (duh, way to go Captain Obvious), it doesn’t float off into space quite as easily. If you look at the ratio of heavy water to normal water in the Earth, those ratios imply that while some of the Earth’s water would have had to have come from outside sources (comets, etc), quite a bit of the Earth’s water must have survived the impact that formed the moon.
Yes, but where did the hydrogen and oxygen in those chemicals come from originally? Most likely it came from water, which came from either the formation of the Earth or from comets (or both). That water got split up and the hydrogen and oxygen went on to combine with other elements. So yes, there are quintillions of chemical reactions that can produce water, but the hydrogen and oxygen atoms that are in those chemicals originally came from water.
If you didn’t have all of that water on the Earth to start with, you wouldn’t have all of those chemicals that you can have reactions with to make water vapor.
I am missing the relevance.
From time to time, electrolysis occurs. It might not happen a lot, but over billions of years, might not the comet water have mostly gone away that way? If so, could we then say that almost all current water on earth came from hydrogen reacting with oxygen?
P.S. I see the point, in the last post, that the hydrogen and oxygen often came from water. Then, I presume it often came from someplace else.
All water in the universe has originally come from hydrogen reacting with oxygen.
Put the proposition another way.
If on the neonatal Earth there existed 2xH2 and 02 molecules in proximity would the available forces on Earth been sufficient to form 2x H20?
The conventional theory is no. But this recent paper in Nature suggests yes.
But whichever the case the number of H and O atoms is unchanged, “merely” their form.
Deleted.
I had tried to ask a question about icy comets to satisfy my 5 year old son’s curiousity but I see his question has been answered.
Thanks, Straight Dope! And particularly @engineer_comp_geek
Presently, the most abundant element on Earth is oxygen. Most of that, of course, is bound up in rocks and sand. At the time of The Collision, its energy might have been enough to break out a lot of that oxygen, allowing it to combine with stuff from the solar wind. Like hydrogen.
Water can be produced in reactions between many different compounds that contain hydrogen and oxygen.
No, iron.
Oxygen is the most abundant element in the atmosphere, oceans and crust.
Essentially, we live on the thin unstable crust of solidified slag on the outside of a ball of molten iron.
Sleep tight!
+1
Canoeing across lakes, I will dip my hand in and scoop a drink of water. Of course I once then paddled by a dead rabbit floating. Big lake, little carcass. No off taste. But off putting.
There’s also this incident.
People are funny about that kind of thing.
Water quality in the Sierra Nevada is studied extensively, and the evidence is that the best water quality is found near the surface of the still water of high altitude lakes (better than streams), probably because of the sterilizing effect of intense UV. So you’re right that contamination from a dead rabbit in a large lake is unlikely to be significant.
Sierra water tests yield good news
Large amounts of poop is the problem. The worst contamination is found in areas frequented by grazing cattle and pack animals.
I thought free hydrogen generally escapes the planet? Since it is the lightest element it floats away to the top of the atmosphere and then the solar wind pushes it off into space. If so, where does all that oxygen find hydrogen to make water?
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I don’t think that’s accurate.
Fish do reproduce in water. But most fish don’t fuck.
I believe in most fish, the female lays eggs, either in a nest or on the seabed, and the male sprays semen in the area, some of which fertilizes the eggs. But no actual fucking, by inserting a male body part into a female body orifice.
Whales & porpoises do fuck, but they aren’t fish.
You are, of course correct.
But the “squirt in general direction” reproductive strategy employed just makes the premise worse.
No, but there might be enough to form 1x H2O
Whoa man, fish are freaks 