The Amount Of Water On Earth

[Boerseun]

Imagine this:

 

There's no water on Earth. It's all gone. You're standing on what used to be the shore, now it's just a barren, dry and dusty wasteland stretching out before you where the sea used to be.

 

Next to you is a pipe leading into the sea. It's a massive pipe, over 1 kilometer in diameter, and where it comes from is anybody's guess. But it terminates on the shore, right next to you, and it delivers water at a speed of 1 kilometer per second. That's a hell of a lot of water - one cubic kilometer of water is being pumped into the emptiness of what used to be the sea, every second. How long do you think you'd have to wait before the sea fills up to the point where you're standing?

 

No. You're wrong. Whatever number you though of, is wrong.

 

It will take 46 YEARS. 46 Years of delivering a cubic kilometer of water per second, every second, to fill up the sea. That's a hell of a lot of water, and kinda puts some perspective on the cavalier methods proposed for terraforming planets.

 

Sorry - not really a science-related thread, but heck...

[Eclogite]

You were right about me being wrong. In a very (very) quick mental calculation I came up with a figure of one hundred and fifty years. So I was in the right order of magnitude erring on the side I suspect you expected most people to avoid.

 

It made ponder - again - why most people don't do rapid arithmetic estimates when faced with this type of quantitative topic. It seems to be superior to guessing.

[Qfwfq]

Before continuing after:

No. You're wrong. Whatever number you though of, is wrong.

I did a bit of "at least" reckoning with one upward rounding to "as much as a billion" square km of surface and figured at least a km average depth, for a final estimate of 30 or more years. Before shifting my eyes back to your post I thought gosh, maybe it could turn out as much as a century or more but no, I had come close enough it seems.

[Moontanman]

Terra forming a planet is indeed a daunting task, providing water to a planet will make Terra forming a very long difficult task, probably thousands if not hundreds of thousands of years. Of course you could just deliver water in the form a deorbiting comet like objects and directing them to collide with your new planet... of course there is a lot more to it than just providing water...

[maikeru]

Imagine this:

 

There's no water on Earth. It's all gone. You're standing on what used to be the shore, now it's just a barren, dry and dusty wasteland stretching out before you where the sea used to be.

 

Next to you is a pipe leading into the sea. It's a massive pipe, over 1 kilometer in diameter, and where it comes from is anybody's guess. But it terminates on the shore, right next to you, and it delivers water at a speed of 1 kilometer per second. That's a hell of a lot of water - one cubic kilometer of water is being pumped into the emptiness of what used to be the sea, every second. How long do you think you'd have to wait before the sea fills up to the point where you're standing?

 

No. You're wrong. Whatever number you though of, is wrong.

 

It will take 46 YEARS. 46 Years of delivering a cubic kilometer of water per second, every second, to fill up the sea. That's a hell of a lot of water, and kinda puts some perspective on the cavalier methods proposed for terraforming planets.

 

Sorry - not really a science-related thread, but heck...

 

Love that thought! It always seems so easy, but actually is nothing short of an absolute nightmare. I was thinking this a few nights ago when I read Moontanman's link on Japan's idea for "floating cities" in the sea.

 

http://scienceforums.com/topic/22716-green-float-concept-a-carbon-negative-city-on-the-ocean/

 

While not exactly terraforming, what we have been doing with the earth is a sort of terraforming, by making the Earth's surface more habitable for us and inhabitable for just about everything else.

 

If we can achieve major projects here on earth, such as controlling global warming, cleaning seas, massive reforestation or restoration of deserts, degraded agricultural lands, etc., I will consider us having a much better shot at terraforming other planets than our own. (But currently few give a damn.)

[Boerseun]

It's just that the scale is staggering... think of it: Look outside and see if you can imagine a cubic kilometer of anything. Look down the street to a point about a kilometer away, and imagine that line extending upwards and sideways, too. That's a hell of a lot of water, every second.

 

But nobody can picture a km³ as flowing out of a pipe, every second. So, imagine a ton of water, 1,000 liters, flowing into the sea every second. That's more like it - it's kinda close to what you'd see flowing over an average sluice. Maybe slightly more or slightly less, but pretty much ball-park. Now - if a pipe like that were to fill the ocean, it would take 46 billion years. A constant flow of 1,000 liters per second will take almost three times the age of the known universe to fill the ocean.

 

There be lotsa water in da sea, mon.

[Tormod]

Very cool thought experiment. Who'd have thunk it. Water, water everywhere!

[Qfwfq]

I must have been even dumber than usual yesterday and forgot to hit the submit button. :doh:

 

Look outside and see if you can imagine a cubic kilometer of anything.

Over here, in favourable contions from a place above most roof and tree tops, I can see the mountains up north of here and also some nearer hills. They aren't cube shaped but the volume of many of them is more than one cubic kilometre.

 

But nobody can picture a km³ as flowing out of a pipe, every second.

According to estimates, totalling the discharge of all rivers into the seas and oceans, it averages something more than a million cubic metres per second (with the Amazon alone contributing about 20%). So with that amount of flow out of the tube it would take some 40 millenia or so.

[CraigD]

Does water evaporate at the same rate?

No. Evaporation depends on lots of factors, and is only one of several ways water can be removed from an land area.

 

I'm wondering how long it took to form present deserts.

Land can become desert fairly quickly once its average rate of water gain - precipitation rate and surface and sub-surface inflow - is less than its rate of total water loss – a combination of evaporation, transpiration by plants, and runoff (“evapotranspiration”) – or the process can take several thousand years.

 

For example, the Aral Sea and its coastal regions went from being productive fishing grounds and green land to a salt desert in about 15 years, due to diversion of its source waters for irrigation, arguably the worst present-day man-made ecological disaster.

 

A much slower transformation took place in many areas of the present day Sahara desert, which were much like the present day Nile valley until around 6000 BC, gradually becoming like they are today by around 2400 BC.

[Moontanman]

All the water on the Earth if combined into a sphere would be 860 miles in diameter, this picture is the size of that sphere compared to the Earth.

 

[Qfwfq]

860 miles in diameter

That would make the time a bit more than 43 years, not far from the OP's 46.

[Mr. Scientistic]

All the water on the Earth if combined into a sphere would be 860 miles in diameter, this picture is the size of that sphere compared to the Earth.

 

Very interesting... :rolleyes:

 

Well, There's a whole lot of water on Earth! Something like 326,000,000,000,000,000,000 gallons (326 million trillion gallons) of the stuff (roughly 1,260,000,000,000,000,000,000 liters) can be found on our planet. This water is in a constant cycle -- it evaporates from the ocean, travels through the air, rains down on the land and then flows back to the ocean. ­The oceans are huge. About 70 percent of the planet is covered in ocean, and the average depth of the ocean is several thousand feet (about 1,000 meters). Ninety-eight percent of the water on the planet is in the oceans, and therefore is unusable for drinking because of the salt. About 2 percent of the planet's water is fresh, but 1.6 percent of the planet's water is locked up in the polar ice caps and glaciers. Another 0.36 percent is found underground in aquifers and wells. Only about 0.036 percent of the planet's total water supply is found in lakes and rivers. That's still thousands of trillions of gallons, but it's a very small amount compared to all the water available. Can't you believe how much water is in the ocean than the water we drink! :)

 

The rest of the water on the planet is either floating in the air as clouds and water vapor, or is locked up in plants and animals (your body is 65 percent water, so if you weigh 100 pounds, 65 pounds of you is water!). There's also all the soda pop, milk and orange juice you see at the store and in your refrigerator… There's probably several billion gallons of water sitting on a shelf at any one time! Hmmm... ;)