# Where does water come from? **URL:** \ **Category:** Factual Questions\ **Created:** [November 29, 2008, 6:13pm UTC](https://boards.straightdope.com/t/where-does-water-come-from/474946 "2008-11-29T18:13:32Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![A\_Dodgy\_Dude](https://avatars.discourse-cdn.com/v4/letter/a/a87d85/32.png) [@A\_Dodgy\_Dude](https://boards.straightdope.com/u/A_Dodgy_Dude)\ **Post date:** [November 29, 2008, 6:13pm UTC](https://boards.straightdope.com/t/where-does-water-come-from/474946/1 "2008-11-29T18:13:32Z")
Or, more specifically, where do water molecules come from? Astronomy shows on the Discovery Channel and the Science Channel always say water came to earth by way of comets and inside meteorites and when the primordial earth cooled down enough, it began to rain. And it rained “for millions of years” and that’s how the oceans were formed. When I turn on the kitchen faucet, the stuff that comes flowing out is more than 4./5 billion years old? Is it really that difficult to get a couple hydrogen atoms to stick to an oxygen atom? ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [November 29, 2008, 6:35pm UTC](https://boards.straightdope.com/t/where-does-water-come-from/474946/2 "2008-11-29T18:35:29Z")
It’s not difficult at all. All you have to do is burn some hydrogen. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [November 29, 2008, 6:43pm UTC](https://boards.straightdope.com/t/where-does-water-come-from/474946/3 "2008-11-29T18:43:34Z")
In order: _Or, more specifically, where do water molecules come from?_ Water molecules come from the combination of hydrogen and oxygen. _When I turn on the kitchen faucet, the stuff that comes flowing out is more than 4./5 billion years old?_ The majority of the water on the surface of the planet is \>4Byr. Water started to condense from hydrogen and the primordial atmosphere sometime between 100Mya and 400Myr after the initial formation of the Earth in the [Hadean](http://www.ucmp.berkeley.edu/precambrian/hadean.html) period. Since the geologic record only goes back to the beginning of the [Archaean](http://www.ucmp.berkeley.edu/precambrian/archaean.html) period, and all existing strata show indications of the presence of liquid water, it is impossible to determine when water formation occurred. Some small fraction of additional water has accrued over the years from interplanetary sources, but the majority of existing water condensed from the original materials. _Is it really that difficult to get a couple hydrogen atoms to stick to an oxygen atom?_ No, it’s really pretty easy, and quite difficult to accomplish the reverse. However, this requires having free or loosely bound oxygen to begin with. Free diatomic and triatomic oxygen is pretty common here on the modern planet Earth (thanks mostly to photosynthetic life) but pretty rare elsewhere in the cosmos. Oxygen tightly bound into some solid oxide or organic molecular species rarely gives up to the weaker covalency offered by diatomic hydrogen, and in fact the spontaneous, non-energetic formation of water typically requires a larger molar concentration of oxygen in some convivial state than hydrogen in their resultant proportions of 1:2. Stranger ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [November 29, 2008, 6:44pm UTC](https://boards.straightdope.com/t/where-does-water-come-from/474946/4 "2008-11-29T18:44:23Z")
> [@A\_Dodgy\_Dude](#): > > Or, more specifically, where do water molecules come from? > > Astronomy shows on the Discovery Channel and the Science Channel always say water came to earth by way of comets and inside meteorites and when the primordial earth cooled down enough, it began to rain. And it rained “for millions of years” and that’s how the oceans were formed. > > When I turn on the kitchen faucet, the stuff that comes flowing out is more than 4./5 billion years old? > > Is it really that difficult to get a couple hydrogen atoms to stick to an oxygen atom? I don’t understand your question. On the contrary, hydrogen and oxigen have such affinity for each other than once a water molecule is formed it is very difficult to separate. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 29, 2008, 7:45pm UTC](https://boards.straightdope.com/t/where-does-water-come-from/474946/5 "2008-11-29T19:45:37Z")
The atoms are ancient(, but the molecules probably aren’t billions of years old. Plants break apart water in the process of photosynthesis, and animals (and plants) produce new water from food and atmospheric oxygen in respiration. And even without biological action, water molecules just sitting around in a container (say, the ocean) will occasionally swap atoms between them. So for any given water molecule, it’s probably fairly recently that that particular oxygen atom combined with those particular hydrogen atoms. ---
**Author:** ![Wiltshire](https://avatars.discourse-cdn.com/v4/letter/w/ea5d25/32.png) [@Wiltshire](https://boards.straightdope.com/u/Wiltshire)\ **Post date:** [November 29, 2008, 9:08pm UTC](https://boards.straightdope.com/t/where-does-water-come-from/474946/6 "2008-11-29T21:08:34Z")
> [@Chronos](#): > > The atoms are ancient(, but the molecules probably aren’t billions of years old. Plants break apart water in the process of photosynthesis, and animals (and plants) produce new water from food and atmospheric oxygen in respiration. And even without biological action, water molecules just sitting around in a container (say, the ocean) will occasionally swap atoms between them. So for any given water molecule, it’s probably fairly recently that that particular oxygen atom combined with those particular hydrogen atoms. It’s a pretty dynamic equilibrium, in fact. “_A randomly selected water molecule will dissociate within approximately 10 hours_”. (according to [http://en.wikipedia.org/wiki/Self-ionization\_of\_water](http://en.wikipedia.org/wiki/Self-ionization_of_water)) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 29, 2008, 10:25pm UTC](https://boards.straightdope.com/t/where-does-water-come-from/474946/7 "2008-11-29T22:25:45Z")
Ah, good, I was hoping a chemist would show up to quantify that. ---
**Author:** ![Wiltshire](https://avatars.discourse-cdn.com/v4/letter/w/ea5d25/32.png) [@Wiltshire](https://boards.straightdope.com/u/Wiltshire)\ **Post date:** [November 30, 2008, 2:01pm UTC](https://boards.straightdope.com/t/where-does-water-come-from/474946/8 "2008-11-30T14:01:13Z")
I’m not a chemist, though. Just your average smart-ass. 😃