Hacker News Reader

Comment by daveslash | Hacker News Reader

I know that truth can be stranger than fiction, but am I the only one a little hesitant to believe that underneath the U.S. alone is a reservoir that is three times the volume of all the oceans combined?

EDIT: I didn't mean to imply that this exists only under the U.S. and nowhere else. I meant to imply "so far, the existence of this reservoir has only only been confirmed under the U.S.; the rest of the world is unknown at this point".

View on HN

This image will give you more idea of how much water there is on the surface in terms of spherical volume.

http://water.usgs.gov/edu/pictures/full-size/global-water-vo...

The title says fresh water

There are three spheres.

1. All water (largest sphere)

2. All of Fresh water.

3. Fresh water in lakes and rivers.

Reference: http://water.usgs.gov/edu/gallery/global-water-volume.html

3D space is infinitely larger than 2D space :)

The deepest point in earth's oceans is 12 km or so, and the average is ~4km. Now, imagine this discovered reservoir is 400 km "deep". It means it will have 3x the volume of all oceans even if its surface area is 30 times smaller.

Drill baby, drill!

It's not a continuous mass of liquid water either, though. It's mostly rock with water in between the grains.

It is not between the grains. It is in the crystal structure of the grains as OH-.

From the article:

  Sure enough, they found signs of wet ringwoodite in 
  the transition zone 700 kilometres down, which 
  divides the upper and lower regions of the mantle.

From wikipedia:

  The transition zone is part of the Earth’s mantle, and 
  is located between the lower mantle and the upper 
  mantle, between a depth of 410 and 660 km.

So, if our planet is roughly 12,000 km in diameter (6,000 km to the center), then this region of depth represents a 100-200 km thick shell where pockets of water may exist. But let's max it out, and try to find the volume ((4/3) * (pi r^3)) using very rough, round numbers to get an upper ceiling.

Hypothetically, if it were a continuous shell of pure, fresh water encapsulating the entire inner mantle and core, and if it happened to be 200km thick, with an inner surface at 600 km deep (the shell's floor starts at a radius of 5,400 km) and an outer surface at 400 km deep (the shell's ceiling stops at a radius of 5,600 km), the intervening space could collect possibly a volume close to 76 billion liters of water.

Compare this to a hypothetical scenario, where our planet's rocky crust has a radius of 5,995 km, and is completely covered in one giant ocean of water 5 km deep (think Water World with Kevin Costner) for a total diameter of 12,000 km, this huge ubiquitous ocean would only contain 2 billion liters of water.

So, in a world of perfect spherical maximums, rounded to the nearest billions in liters, this subterranian zone could contain 38 times the water we currently observe on the surface of the earth.

You dropped some zeros. A billion liters is a cube 100 meters on a side, more like a drop than an ocean.

Wait, you're right. I think I dropped about maybe 4 zeroes off the exponential notation. Strike the "billion" and make it like 10^11th or 10^12th power. Either way, I think the ratios still work.

...and oh yeah, by the way, my units were the wrong order of magnitude; should've been kiloliters (not just liters), on top of the exponential notation.

It makes perfect sense when you plug the numbers. They're talking about a thin layer of extremely dry, hot rocks in the earth's mantle. Something like 1-2% water by weight [0] in ringwoodite -- about 35-80 grams/liter. (Liquid water at the surface is >1,000 grams/liter). The catch is, it's a staggering volume: the earth's mantle is ~3,000 km thick, and the comparatively "thin" layer they're looking at, the transition zone, is ~250 km [1] -- this compared to the oceans' depth of ~4 km [2].

    "The water storage capacity of the upper and lower
    mantles is less than 0.2 wt%. The transition zone has a
    storage capacity of approximately 0.5–1 wt% due to a
    water solubility of about 1–3 wt% in wadsleyite and
    ringwoodite, which are the major con- stituents of the
    transition zone. Thus, the transition zone may be a
    major water reservoir in the Earth’s interior."

[0] http://mon.univ-montp2.fr/claroline/backends/download.php?ur...

[1] https://en.wikipedia.org/wiki/Transition_zone_%28Earth%29

[2] https://xkcd.com/1040/

The Earth is huge and the oceans cover only a tiny sliver of the surface. Doesn't really surprise me.

They said they only have evidence underneath Earth. Whether it's under other countries is still under investigation. To emphasize my point, note how he states that if this water were all to rise to the surface, then only the mountain tops would be visible.

The earth is covered by 71% water.

http://www.universetoday.com/65588/what-percent-of-earth-is-...

Yes, but a surface is only two dimensions, and we're measuring a volume (three dimensions). The average depth of Earth's oceans is a paltry 4.3 km.

Got it. Misread what was said.

Tiny sliver? There is approximately 2.4 times more water on the surface of earth than there is land: http://www.wolframalpha.com/input/?i=earth+surface+covered+b...

Except the water is almost entirely less than 5 miles deep, which is a sliver when we're talking about something with a radius 1000 times that.

"So far, Jacobsen only has evidence that the watery rock sits beneath the US. He now wants to find out if it wraps around the entire planet."

Right. I didn't mean to imply that the water is only under the U.S. I meant to say that under the U.S. there is 3 times the volume of the world's oceans. That seems like an awfully large amount of water for an area that comprises around 2% of the Earth's surface. If this rock wraps around the entire Earth evenly, that suggests that there is 150 times the volume of water of all the Earth's oceans 700 kilometers down. The idea that the oceans, which cover 70% of the surface and may be miles, deep only make up .007 of the volume of water on Earth blows my mind.

EDIT: 2% = 1/50th of the surface. 3-oceans * 50 = 150. (1 * all earth's oceans) / (150 * all earth's oceans) =~ 0.00666...

Volume of oceans = 1,335,000,000 km^3 [1] Volume of earth = 1.08321e+12 km^3 [2]

So oceans only occupy 0.00123% of the Earth's volume. There's a lot of room below us.

[1]: http://ngdc.noaa.gov/mgg/global/etopo1_ocean_volumes.html

[2]: http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.htm...

You cannot linearly scale volume under a surface in a sphere by the surface difference. If Earth was a cylinder - then you could ;)

So it will be significantly less than 150 times more than surface oceans. Still huge probably.

'Merica

If you're going to do it right it's actually 'Murca' these days. You have to get the southern accent fully in.

That's a TEXAN accent, pilgrim.

Reply on news.ycombinator.com