Age of Water

Factual Questions
21

[QUOTE=Khadaji]
I had a high-school science teacher who was fond of telling us that in any glass of water there were so many molecules of water that at least one of them had had to have passed through our favorite movie star at one time. He thought this would somehow seem cool to us…
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My teacher had a similar story, but involved breathing at least one molecule that had been exhaled by Julius Ceaser as he said, “Et tu, Brute?”

22

Anything which respires (animals all the time, and plants some of the time) produces water. Plants, when they photosynthesize, consume water. These processes, like the biological CO[sub]2[/sub] cycle, are balanced (in fact, any imbalance in the one will also be an imbalance in the other, since they involve the same chemical reactions).

Now, the atoms that the water is made of are very old indeed. The oxygen atoms all predate the Sun (and are hence at least 5 billion years old), having been formed in some previous-generation star which died and contributed some of its material to the proto-solar nebula. The hydrogen atoms, meanwhile, were the first things (given a common understanding of “thing”) to form in the Universe, and so date back over 13 billion years.

23

[QUOTE=twickster]
Layperson’s question here. Occasionally I’ll see a drop of water on the tip of a leaf of my pothos (houseplant). Since said leaf is a couple of feet from the roots of the plant (which is, obviously, where I water it), I’ve never been clear where it came from. Is this a byproduct of photosynthesis?
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[QUOTE=Christopher]
No, photosynthesis consumes water.
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[QUOTE=twickster]
So where does that water come from?
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[QUOTE=Tahssa]
Probably from the moisture in the air.
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If you’re seeing an actual drop, it could very well be guttation, as noted above.

However, plants do indeed give off significant amounts of water via transpiration. The water is in the form of vapor, though. Plants draw water from the ground and put it into the air. This has a significant effect on the climate in areas with heavy vegetative growth.

Rather than moisture on plant leaves coming from the air, then, the converse is the case. The moisture in the air can be often be largely due to transpiration from plants.