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Couldn't believe this statistic


starman1969
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Just thought I'd look up how much of the world's population lives in the southern hemisphere, out of interest.

According to Wikipedia it's around 10-12%. Does this percentage of people realise how lucky they are?

They seem to get all the best stuff down that way as well, it's not fair. The weather in most of the places is pretty good too.

I think we deserve a free invite to Australia or somewhere.

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To be fair the Southern hemisphere has only 19% of the Earths land mass and much of it inhabitable.

Quite odd that, really. And you'd think the weight of all that land on top would cause the planet to tip upside down. Antarctica must be very heavy.

James

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Fascinating stuff. Bit off on a tangent, but that reminded me of the illustration showing the entire world's water can be contained within a sphere with a radius of 693 kilometres, of which only 0.77% is liquid fresh water! Less water, in fact, than is estimated to be on Jupiter's moon Europa (on the left in this image).

water_on_earth_vs_water_on_Europa_400w.jpg

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I find that impossible to believe. In fact, I'll go so far as to say that diagram's wrong.

Well, the total volume of a sphere is 4/3 pi r3. A radius of 693km would give a total volume of about 1.4bn km3 (just under). Wikipedia gives a figure for the total volume of water on Earth to be 1,338,000,000 km3, so certainly that looks to be in the right ball-park. To me the scale of the sphere relative to North America looks about right, too.

Give us some evidence to the contrary, by all means. I'm willing to be persuaded by a sufficiently compelling argument.

James

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Quite odd that, really. And you'd think the weight of all that land on top would cause the planet to tip upside down. Antarctica must be very heavy.

James

Well I have no idea of the numbers and density's involved but maybe it's because the surface area of the planet only represents a very small fraction of the overall mass?

Plus I guess Antarctica is kind of a polar opposite.

As soon as I hit submit I thought, hang on.....duh @ me.

It's OK, we knew what you were getting at. :)

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Well, the total volume of a sphere is 4/3 pi r3. A radius of 693km would give a total volume of about 1.4bn km3 (just under). Wikipedia gives a figure for the total volume of water on Earth to be 1,338,000,000 km3, so certainly that looks to be in the right ball-park. To me the scale of the sphere relative to North America looks about right, too.

Give us some evidence to the contrary, by all means. I'm willing to be persuaded by a sufficiently compelling argument.

James

I generally work by the rule that if James is saying it's right, it probably is. :D

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I once read ( do not know if its true ) that the depth of the worlds oceans can be compared to immersing a table tennis ball in water then removing it and the water covering the ball would represent the depth of the worlds oceans on the same scale ( I know what I mean !! )

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I once read ( do not know if its true ) that the depth of the worlds oceans can be compared to immersing a table tennis ball in water then removing it and the water covering the ball would represent the depth of the worlds oceans on the same scale ( I know what I mean !! )

I can understand what you mean. Maybe the illustration above is accurate. Very surprising.

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it would depend on the depth of water - I dont think on the scale of things land mass would matter too much as i think the deepest of oceans is about 7 miles and the mount everest about 5.5 miles.

The earth is about 8000 miles diameter- so about 0.3 % max uneven land mass

99.7% the same size circle with evenish weight. so we probably wouldn't keel either way :smiley:

However if John Prescott was to go to ozzy the whole dynamic would change and we would fly off into outer space :grin:

Edited by Pig
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The Mariana Trench is about 10km deep. If we said that the average depth of water is therefore 5km (almost certainly an overestimate, I feel), that water covers seven tenths of the planets surface, treat the Earth as a sphere and accept that the amount of fresh water is tiny compared to the oceans then it's possible to calculate an approximate upper limit for the amount of water on the planet just by taking the volume of 7/10ths of a 5km thick shell at the surface of the Earth. That works out as 1.8bn km3.

Looking up the accepted figure for average ocean depth on Wikipedia and using that instead reduces the figure to 1.36bn km3, so the image of that sphere of water does look about right to me.

James

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For what it's worth, I don't think Ken is wrong to express some disbelief here. That seems like a tiny amount of water and it's sensible in such cases to attempt some sanity checking on the data.

It struck me whilst I was just out feeding the chickens that scientists consider that the wide availability of a polar molecule in liquid form at "normal" temperatures may be an absolute requirement for life to exist. It may well be that were it not for that little bubble of water not only would we not exist, but Earth might be just another barren lump of rock.

James

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If someone could work out how to turn all the atmosphere into a liquid and show you the even smaller size of that sphere I'd suspect it'd be a real eye opener. In geological scales we really do exist in an impossibly small sliver of an environment. So incredibly fragile and yet from within so mindblowingly diverse.

There is no doubt in my mind that life finds a way in every single possible place that it can. I'd expect there to be life everywhere where the conditions are right -and I suspect that the conditions that we have on earth are not the only means of life support. All you need is an energy source and tidal forces on moons around gas giants are likely to be far more prevelant than water planets near appropriate suns.

Edited by Stargazing00
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There is no doubt in my mind that life finds a way in every single possible place that it can. I'd expect there to be life everywhere where the conditions are right -and I suspect that the conditions that we have on earth are not the only means of life support. All you need is an energy source and tidal forces on moons around gas giants are likely to be far more prevelant than water planets near appropriate suns.

I'm broadly in agreement that "life will find a way". I believe the reason that liquid water is considered pretty much a necessity however is because it is a polar molecule and the energy differential across the molecule can allow chemical reactions to take place in liquid water that probably could not happen otherwise. My understanding is that the belief is that you need not only an energy source, but also the ability to create an energy differential effectively "on demand" and polar molecules allow that to happen. There are other polar molecules (ammonia?) but there may be other chemical and physical properties of water that make it a more viable choice.

Brian Cox covered some of this in his recent "Wonders of Life" series though I'm sure I've seen it explained better elsewhere.

James

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