Starship Asterisk*

ro_star wrote:this really helps visualizing how little water there is in fact on the earth and how easy it is to pollute it all - most of it is saltwater, and billions of people have no access to fresh drinking water - so if we don't take care of the water we have, to keep it fresh and unpolluted, there is even the risk that a similar civilization with more technical knowledge may one day send an automated probe to remove the water from earth because they happen to need it since they polluted theirs; that's why we should set an example and keep it clean

I hope that last sentences was tounge-in-cheek: We should keep our water clean because it tastes better that way. Any civilization advanced enough to send an automated probe our way to get our water would neither need to nor want to do that. In fact, they would probably send us a machine to purify ours for our use as a gesture of good will. But maybe I'm being overly optimistic here. My glass is half-full.

The problem with Earth's fresh water supply is that it is mostly inaccessible. It just isn't available where it is needed most. If all our surface water someday instantly becomes poluted (or otherwise made non-potable), I wonder how long it would take for natural processes to fix things: What is the global rate of evaporation and condensation? (Compared to the total volume of the Earth's water?) Anyone know?

Chris Peterson wrote:

drollere wrote:
a sphere 1400 kilometers in diameter of water. ok ... now let's calculate how much trash, garbage, polluted runoff and sewage is dumped into it each year by 7 billion humans. maybe you can tint it brown in proportion. blue is much too optimistic.

That works out to each person on the planet having their own little cube of water about 600 meters on a side.

http://en.wikipedia.org/wiki/Water_use wrote:
<<The water footprint of an individual refers to the sum of his or her direct and indirect freshwater use. The direct water use is the water used at home, while the indirect water use relates to the total volume of freshwater that is used to produce the goods and services consumed.

The average global water footprint of an individual is 1,385 m³ per year[: a cube of water about 11 meters on a side].

The average consumer in the United States has a water footprint of 2,842 m³ per year[: a cube of water about 14 meters on a side].

flash wrote:
What is the global rage [sic] of evaporation and condensation? (Compared to the total volume of the Earth's water? Anyone know?

http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29 wrote:
Approximately 505,000 cubic kilometres of water [i.e., 1.3% of all the fresh water] falls as precipitation each year; 398,000 cubic kilometres of it over the oceans and 107,000 cubic kilometres over land. Given the Earth's surface area, that means the globally averaged annual precipitation is 990 millimetres, but over land it is only 715 millimetres.

Chris Peterson wrote:

neufer wrote:Note that both here and in today's APOD no one bothered to remove the snow & ice fields.

That bothered me instantly when I first saw this image a few days ago. Most of the icy areas have been more-or-less fudged out to an acceptable degree, but it hurts to see Greenland represented the way it is. It should look like northern Canada. Granted, the amount of water tied up in the Greenland icepack wouldn't visibly change the size of the water sphere, but leaving it white really detracts from the image, IMO.

Greenland isn't white, it's colored the same as the continental shelf. The deserts of North Africa appear whiter to me.

That's a great graphic. I wonder how big would be the ball of all the crude oil ever pumped out of the earth combined with all the assumed reserves? Quite tiny on this scale I would imagine.

bystander wrote:Greenland isn't white, it's colored the same as the continental shelf. The deserts of North Africa appear whiter to me.

It looks like icepack to me. Not white in absolute colors, but white within the sort of shading used. You can see the non-glaciated coastlines of Greenland. In any case, coloring Greenland the same as continental shelf is still wrong. It should look like northern Canada, being made of continental crust.

I never saw this image before APOD posted it. I love it and have shared it widely today. If anybody can point me to an answer to the following questions, I'd be grateful:

1. How did such a tiny amount of water come to cover 70% of the planet's surface? Why not 25% or 50% or 90%?

2. How much has the water coverage of the Earth varied over geological time? What portion of the surface was covered by oceans 2 billion years ago, or half a billion years ago?

ruprecht147 wrote:I never saw this image before APOD posted it. I love it and have shared it widely today. If anybody can point me to an answer to the following questions, I'd be grateful:

1. How did such a tiny amount of water come to cover 70% of the planet's surface? Why not 25% or 50% or 90%?

Fundamentally, it's a consequence of the flatness of the Earth's surface and the total amount of water. The flatness results from our relatively high gravity, which limits how high mountains can get, and how deep valleys can get (with the highest spots representing thick continental crust, and the lowest representing thin oceanic crust). It's uncertain where the water came from- whether it was part of the protoplanet or was delivered later.

2. How much has the water coverage of the Earth varied over geological time? What portion of the surface was covered by oceans 2 billion years ago, or half a billion years ago?

That is unknown. The ratio of land to sea is determined by the ratio of continental crust (which is old) to oceanic crust (which is young). Oceanic crust recycles much faster than continental crust. The continents move about in what is called the supercontinent cycle, but it is uncertain if the ratio of continental to oceanic crust has changed much in several billion years. During the first billion years of Earth's existence it was probably covered only with oceanic crust, in which case the planet was probably covered with a single ocean.

Chris Peterson wrote:

neufer wrote:Note that both here and in today's APOD no one bothered to remove the snow & ice fields.

Granted, the amount of water tied up in the Greenland icepack wouldn't visibly change the size of the water sphere, but leaving it white really detracts from the image, IMO.

I am often overwhelmed by the sheer volume of knowledge that’s available. I was curious about the letters I M O. So, I Googled “IMO” and the responses were numerous. One in particular gave 41 meanings of IMO and then stated that it had 136 more! A few, with some stretch of the imagination, might have something to do with astronomy but, rather than reading all 177 and then guessing, I thought I would simply ask what did you mean by your “IMO”?

Chris Peterson wrote:

ruprecht147 wrote:1. How did such a tiny amount of water come to cover 70% of the planet's surface? Why not 25% or 50% or 90%?

Fundamentally, it's a consequence of the flatness of the Earth's surface and the total amount of water. The flatness results from our relatively high gravity, which limits how high mountains can get, and how deep valleys can get (with the highest spots representing thick continental crust, and the lowest representing thin oceanic crust). It's uncertain where the water came from- whether it was part of the protoplanet or was delivered later.

So it sounds like more water would mean a larger area covered by oceans, and less water would mean a smaller area? Somehow I'm thinking the answer might be more complicated. Generally, the idea that Earth's oceans originated from impacts by icy asteroids (or maybe comets) seems widely endorsed by astronomers these days -- Sean Raymond has done a series of articles on that topic. The trick seems to be figuring out how we got exactly as much water as we did.

Mactavish wrote:I am often overwhelmed by the sheer volume of knowledge that’s available. I was curious about the letters I M O. So, I Googled “IMO” and the responses were numerous. One in particular gave 41 meanings of IMO and then stated that it had 136 more! A few, with some stretch of the imagination, might have something to do with astronomy but, rather than reading all 177 and then guessing, I thought I would simply ask what did you mean by your “IMO”?

An extremely common Internet term, In My Opinion. Sometimes seen as IMHO, but I'm not humble enough to use that one <g>.

ruprecht147 wrote:So it sounds like more water would mean a larger area covered by oceans, and less water would mean a smaller area? Somehow I'm thinking the answer might be more complicated.

The ratio of continents to oceanic basins is determined by tectonic processes. While it's true that more water would mean larger oceans, and less water would mean smaller ones, the changes would be relatively small unless you look at very large changes in water volume. Even with less water, the ocean basins will still be full, just not as deep. And with more water, the coastlines would move in a bit, but not far- the oceans would get deeper. Mainly you'd see the shifts along the boundaries between oceanic and continental zones.

Mesas, flat-topped elevated structures, are common on Mars. It is fascinating to think that the Earth's continents are slightly like the mesas on Mars: They rise, often quite abruptly, from the bottom of the sea, and then they flatten off until they suddenly slope abruptly down to the bottom of the sea again.

It is good for us that the Earth has its giant mesas or continents. We would have had to be dolphins if the continents hadn't been there, and then we would have lacked hands, which would have made it difficult for us to build any real civilization.

Maybe we wouldn't even have been dolphins: If the Earth had never had continents, it might have been useless for the creatures of the ocean to develop lungs.

We might all have been sharks, or octopuses.

Ann

neufer wrote:

alter-ego wrote: FYI, a conservative average H₂O content ≈1% within the sphere of air, so its water contribution is minor (as you would think) compared to the surface water.

Average H₂O content ≈0.4% within the sphere of air.

I read that too, and I picked the larger number as a conservative (high) estimate. To quote the same article:

[b][color=#0000FF]http://en.wikipedia.org/wiki/Atmosphere_of_Earth[/color][/b] wrote:Air also contains a variable amount of water vapor, on average around 1%.

It's really not important what the exact number is, just that its small. In fact, I wouldn't bet on a number. The "above illustration" link has this detailed graphic: Dang, I'm feeling thirsty all of sudden.

alter-ego wrote:

neufer wrote:

alter-ego wrote: FYI, a conservative average H₂O content ≈1% within the sphere of air, so its water contribution is minor (as you would think) compared to the surface water.

Average H₂O content ≈0.4% within the sphere of air.

I read that too, and I picked the larger number as a conservative (high) estimate. To quote the same article:

[b][color=#0000FF]http://en.wikipedia.org/wiki/Atmosphere_of_Earth[/color][/b] wrote:
Air also contains a variable amount of water vapor, on average around 1%.

It's really not important what the exact number is, just that its small. In fact, I wouldn't bet on a number. The "above illustration" link has this detailed graphic: Global Water Distribution.JPG

Dang, I'm feeling thirsty all of sudden.

Mid-latitude air at the ground may be around 1% water vapor on average
but globally water vapor is ≈0.4% within the sphere of air.

The atmosphere has a mass of about 5×10¹⁸ kg.

0.4% of that is 2×10¹⁶ kg which amounts to just
0.00142% of the 1.4087 ×10²¹ kg of total water.

(Approximately 50.5×10¹⁶ kg water [i.e., 25 times the average atmospheric content] falls as precipitation each year.)

Is the water droplet drawn to scale wrt to the Earth's size? If only this much volume of water is there on the Earth (even if it saline) then its scary. I always thought 70% of Earth is water, but I understood from this APOD that 70% surface of area of Earth is water, and not volume. Is my understanding correct? Wish you guys had quoted some numbers for comparision and understanding.

abhagwat wrote:Is the water droplet drawn to scale wrt to the Earth's size? If only this much volume of water is there on the Earth (even if it saline) then its scary. I always thought 70% of Earth is water, but I understood from this APOD that 70% surface of area of Earth is water, and not volume. Is my understanding correct? Wish you guys had quoted some numbers for comparision and understanding.

Your (new) understanding is correct. To scale, all the water on the Earth is nothing more than a film on the surface (on a standard 30 cm globe, the oceans are less than a tenth of a millimeter deep- around the size of a human hair).

APOD Robot wrote: All the Water on Planet Earth

Explanation: How much of planet Earth is made of water? Very little, actually. Although oceans of water cover about 70 percent of Earth's surface, these oceans are shallow compared to the Earth's radius. The above illustration shows what would happen if all of the water on or near the surface of the Earth were bunched up into a ball. The radius of this ball would be only about 700 kilometers, less than half the radius of the Earth's Moon, but slightly larger than Saturn's moon Rhea which, like many moons in our outer Solar System, is mostly water ice. How even this much water came to be on the Earth and whether any significant amount is trapped far beneath Earth's surface remain topics of research.

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I wondered how much atmosphere earth got.

The effective volume (8.2 kilometers up) of earth's atmosphere is about 4.2 billion cubic kilometers,
the actual volume (100 kilometers up) where the Karman limit is, 51 billion cubic kilometers.

Earth water volume is approximately 1.3 billion cubic kilometer.

We got less water than air...do not pee when you are in water!

Moonlady wrote:I wondered how much atmosphere earth got.

The effective volume (8.2 kilometers up) of earth's atmosphere is about 4.2 billion cubic kilometers,
the actual volume (100 kilometers up) where the Karman limit is, 51 billion cubic kilometers.

Earth water volume is approximately 1.3 billion cubic kilometer.

Unlike water, the volume of the atmosphere is strongly dependent on its temperature and pressure. So comparing volumes is like comparing apples and oranges, unless you find a way to normalize things. The total mass of water is several orders of magnitude greater than the mass of the atmosphere. If you compressed the atmosphere into liquid, its volume would be much less than that of all the Earth's water.

It's not such a simple comparison.

Chris Peterson wrote:

Moonlady wrote:I wondered how much atmosphere earth got.

The effective volume (8.2 kilometers up) of earth's atmosphere is about 4.2 billion cubic kilometers,
the actual volume (100 kilometers up) where the Karman limit is, 51 billion cubic kilometers.

Earth water volume is approximately 1.3 billion cubic kilometer.

Unlike water, the volume of the atmosphere is strongly dependent on its temperature and pressure. So comparing volumes is like comparing apples and oranges, unless you find a way to normalize things. The total mass of water is several orders of magnitude greater than the mass of the atmosphere. If you compressed the atmosphere into liquid, its volume would be much less than that of all the Earth's water.

It's not such a simple comparison.

Thanks Chris, sure you are right that elements comparing in different states like solid, liquid, gas and plasma is not correct and mass cant be calculated that way too.
I thought (unprofessional) I could somehow add to this day's picture which shows earth solid and water liquid, a size of atmosphere gas volume as it is in the condition of each
elements, a condition that is in real life, so how big would be a globe of atmosphere-layers, or in comparison in cubus, would it be less or more than water...do I make sense?!
I hope your hair does not stand right now!

@Moonlady:

http://asterisk.apod.com/viewtopic.php? ... 64#p175560
http://asterisk.apod.com/viewtopic.php? ... 55#p175582

http://www.sciencephoto.com/images/imag ... =690550330

And THIS Tiny Sphere is All the World’s Water *That We Can Use*

[i]Credit: Jay Kimball, 8020Vision[/i]

---

A few days ago, we wrote about a remarkable graphic released by the USGS, showing all the water on Earth—freshwater, saltwater, water vapor, water in plants and animals; all of it—rolled into a sphere.

That sphere was only 860 miles in diameter, fitting comfortably between Salt Lake City and Topeka, Kansas, on a map. It was striking, especially considering that the water available for humans use in our daily lives is only a very small fraction of that; the vast majority of the Earth’s water is saltwater, and most of the freshwater is tied up in glaciers.

How big would a sphere of just the freshwater available to humans be? Reader Jay Kimball of 8020Vision, his interest piqued, went ahead and made such a graphic:

That sphere—the sphere representing the freshwater available to humans—has a diameter of just 170 miles. Head to his blog to see the math.

ro_star wrote:...there is even the risk that a similar civilization with more technical knowledge may one day send an automated probe to remove the water from earth because they happen to need it since they polluted theirs; that's why we should set an example and keep it clean

ro_star, you have been watching too much 'V'. Taking our water is much harder than taking water from an Oort cloud object. Not only do you have to fight off the pesky humans but you have to lift the water out of a double gravity well; the Earth's and the Sun's. Any civilization in need of water can find plenty in the outer reaches of most solar systems as icy worlds. Compared to the energy required to drag water between stars, melting ice is child's play. Remember Pluto didn't cease to exist when it got demoted from planet status. It became the type object for a whole class of icy worlds. There are approximately a trillion ice worlds beyond Neptune.

[quote="ann']It's not having huge amounts of water that counts. It's having the right amount of water that counts, and having it in the right phase states - solid, liquid and gaseous - and having it where it can serve as a lubricant for the forces of plate tectonics and volcanism, and having it as a catalyst for life.

[/quote][/quote][/quote][/quote][/quote][/quote][/quote]

ann, I like you analogy about how water works with respect to life. What life needs is not water volume but surface area. Life lives on surfaces because life captures energy and once life forms a surface it denies energy to any life beyond that surface. Life particularly likes to exist on planar boundaries between two different resource rich zones (e.g. sky with light above, soil with water and nutrients below). So you are correct that life doesn't need more volume of water. But I think you are wrong about needing the right phase states. Life needed liquid water to get started but life is young; complex life on Earth has only existed for 600 million years. We puny humans think that is a long time but in cosmic terms it is a blink of an eye. 400 million years ago, desert plants would have been a laughable idea, and flower-forests (angiosperms, the last great advancement in plants) have only been around for about 100 million years. We may think that ice forests are a laughable idea now but life will find a way to make them eventually and then vacuum forests and then the huge surface area of the outer icy worlds of Sol will be open to them.

My guess is when the solar system was still very young, the Earth collided with a third body the size of that ball - which I expect would make for a tremendous collision - that a) broke off a huge chunk of it and created our moon and b) was mostly water ice (like some moons of Jupiter or Saturn) which melted because of Earth's proximity to the Sun and voilà there's our oceans. Of the other rocky planets, Mars wasn't hit by the same 'fortune' and Venus and Mercury are way too hot (and Mercury too small) to keep it.