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All of Earth's water in a single sphere (2019)

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Re: All of Earth's water in a single sphere (2019)

#181

Post by morepork »

rmah wrote: post #30

Just a few quick calculations to make it more relatable... They say the smallest sphere of freshwater lakes and rivers amounts to 93,113 cu km. There are 1 bil cu m per cu km. With a global population of 8.2 bil people, that comes to 11,355 cu m per person. That's a 22.5 meter wide/deep/tall cube (or about 7 or 8 stories tall building). If we use the sphere that includes groundwater, 10,633,450 cu km. Then we end up…

It's interesting to consider that there's about 26,000,000 km^3 of ice in the Antarctic ice sheet, which would give you a much larger ~150 m^3 cube of ice per person. That's not including the Greenland ice sheet or any sea ice.

Re: All of Earth's water in a single sphere (2019)

#182

Post by TheRealPomax »

The problem with this sphere is that people are terrible at understanding the mind boggling scale represented by "height" here. It looks like a tiny drop that "fits on the US". Instead it has a diameter of 860 miles. That's a ball of water that reaches all the way to outer space...

...and then keeps going for another 800 miles.

Re: All of Earth's water in a single sphere (2019)

#183

Post by dredmorbius »

hn_throwaway_99 wrote: post #178
dredmorbius wrote: post #159

NB: The infographic and articles are based on a 1993 publication. More recent research, from about 2017, suggests that there's about as much water in Earth's mantle as in all the oceans, so we either need another drop roughly the volume of the first, or the second drop should be greatly expanded. See: "There’s as much water in Earth’s mantle as in all the oceans" (2017) https://www.newscientist.com/article/2133963-th…

Does any of that water, though, ever make it onto the Earth's surface? I'm guessing not, or only miniscule amounts over geologic time through volcanism. For all intents and purposes, I think only counting "surface" water is more useful and intuitive. It's essentially any water that can participate in the hydrologic cycle on Earth, and that water locked beneath the crust doesn't really "matter" for what I think the in…

The fundamental problem with complex phenomena is in defining the domain(s) of interest.

If we want to talk about the total amount of H2O around, on, or in the Earth then inclusion makes sense.

If we want to talk about water interacting with the surface environment (atmospheric, sea, ice cap, fresh, and subsurface aquifers and tectonic water), then splitting those into distinct categories probably also makes sense. In which case we can also show the subsurface water.

How much mantle water does make it to the surface over time is a good question. I've no idea though I'd suspect that some does through geothermal and tectonic activity. The more interesting question might be how we'd determine this (all but certainly through isotopic composition), and if a net flux could be determined.

Over geological time, additional reservoirs of water are significant simply because surface water boils off into space over time, with estimates I've seen of up to 25% of Earth's original allotment having done so over 4.5 billion years or so. As the Sun eventually grows warmer, this rate will increase. At the same time, tectonic activity will slow.

Note that there's a fair bit of water transport through the lower crust / upper mantle as oceanic plates subduct under continental plates, with the water absorbed into the oceanic plates playing a major role in volcanism at those plate boundaries, e.g., along the "Rim of Fire" surrounding the Pacific basin.

Re: All of Earth's water in a single sphere (2019)

#184

Post by sfink »

stavros wrote: post #180
Intralexical wrote: post #114

Earlier quoted context omitted.

"Squirt with a spray bottle" is a nice euphemism for throwing asteroids at. https://en.wikipedia.org/wiki/Origin_of_water_on_Earth#Aster...

They mean in terms of the ratio of water to rock.

Well, the spray bottle was more to spread the water out into a thin layer as opposed to something like crashing an icy asteroid in at one spot.

I have a mental image of a gigantic cosmic being grabbing the Earth, wiping off the wet stuff with a rag, and bowling it at Proxima Centauri.

Re: All of Earth's water in a single sphere (2019)

#186

Post by sfink »

AnimalMuppet wrote: post #56
dylan604 wrote: post #44

Earlier quoted context omitted.

> They are polynomial I don't think this word means what you think it does. Or I don't. Exponents are just the number the value is raised. Squaring a value just uses an exponent of 2 where cubing uses an exponent of 3. Polynomials are x^2 + x + 1 type of equations. But admittedly, it has been 30+ years since I've thought about them at that level, so maybe I'm the one with fuzzy groking

"Polynomial" meaning x^n. "Exponential" meaning e^x. Exponentials eventually grow much faster than polynomials, no matter what the exponent is. I mean, look, in v = x^3, the "3" is an exponent. But it's not an exponential function because the variable isn't in the exponent.

> Exponentials eventually grow much faster than polynomials, no matter what the exponent is.

Since we're being pedantic, that last clause should be: "as long as the exponent is greater than 1."

Re: All of Earth's water in a single sphere (2019)

#187

Post by syndicatedjelly »

mistercow wrote: post #152

I think it’s important to keep in mind that if you did this same visualization on a planet with ten times Earth’s radius, but the same ocean depth and water distribution, then the water blobs would seem even smaller in comparison to the planet. I’m just not sure it’s a particularly useful illustration to compare the volume of water on a planet to that of the planet itself.

Why is this confusing? We aren't comparing planets by amount of water they have. I thought the goal of this visualization was just to make a point - the amount of fresh water in rivers and lakes appears to be the size of a large metropolis in radius. Seems like a cool way to show scale of water resources

Re: All of Earth's water in a single sphere (2019)

#188

Post by sfink »

asadm wrote: post #104
srameshc wrote: post #99

We always talk about how scarce freshwater is but this image reprenstation has made it difficult to imagine how much supply do we have for an ever growing human population, the growing demand for water and how long will it last.

Does water leave earth when used?

It's more extreme than that, it stops existing.

The comment you're replying to is about fresh water. Which becomes non-fresh when it mixes into seawater or waste or pollution. No need to leave the Earth.

Admittedly, it's probably better to talk about the cycle, since non-freshwater will be automatically converted back to freshwater via solar energy. But the rate can be slowed—eg, dump a bunch of toxic stuff in one place, it'll drain to a river, now everything from that point and downstream is no longer freshwater. Or pump up enough groundwater. Or inject toxic crap down where the groundwater lives.

We're quite good at reducing the total amount of freshwater available.

Re: All of Earth's water in a single sphere (2019)

#190

Post by ClumsyPilot »

DiggyJohnson wrote: post #145
FredPret wrote: post #31

Earlier quoted context omitted.

"Groundwater" is a little ambiguous - H2O in the mantle is also "ground water", no?

No, it’s completely inaccessible. Unless you are just playing word games, then sure.

Geologically it probably isn’t. If all surface oceans disappeared, some of that water would likely come out to the surface and form new bodies of water, over millions of years.
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