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Antipodes

I've messed around a bit with the map I found of antipodes on Wikipedia to produce this, outlining the northern hemisphere bits:



The only parts of the continental USA with land antipodes are a small patch in Montana, opposite Kerguelen Island (which also straddles the border into Canada), and two small patches of Colorado which are opposite the remote Île Amsterdam and Île Saint-Paul. Parts of the far north of Canada and Alaska, and most of Greenland, are antipodal to the coast of Antarctica.

The only parts of Europe with land antipodes are the parts of Spain and Portugal opposite New Zealand (which also grazes Morocco), and Svalbard, which has antipodes in Antarctica.

Africa contains the antipodes of a number of Pacific islands: Hawai'i, and everything from French Polynesia to Vanuatu and New Caledonia.

South America contains the antipodes of parts of eastern Asia: most of eastern China (with Mongolia mapping onto the tip of Argentina and Chile), Taiwan, sothern Vietnam, Cambodia, the Philippines, Malaysia, Brunei, and most of Indonesia.

It's not much, is it?

Comments

( 6 comments — Leave a comment )
tortoise
Jan. 9th, 2010 06:18 pm (UTC)
The interesting question to me, and one I've never seen explicitly answered, is how the the total area of antipodal land corresponds to what you'd expect if land was randomly distributed over the globe.

It's presumably quite a bit less, given that the Pacific Ocean essentially takes up an entire hemisphere, but I've never seen any numbers that would let me determine exactly how much less...
del_c
Jan. 9th, 2010 06:38 pm (UTC)
Earth is about 29% land, so a purely random chance of antipodal land should be about 29% of the land, or about 8.5% of the total planetary area.

But we're only 180 million years from the most recent "all one continent" period, so it's closer to nothing than it is to eight percent.
tchernabyelo
Jan. 9th, 2010 09:05 pm (UTC)
Given how widely distributed the land has become since then, however, I am not sure that's an adequate explanation. There's obviously a big mismatch in the amount of land area per hemisphere, which will lead to a reductoin in the possible antipodean land, but it's interesting that the predominant area of land in the north (i.e. the latitudes with most land/least sea) happen to correspond neatly with the areas in the south that are almost entirely ocean. And the way that on the above map North America fits neatly into the Indian Ocean while Africa pushes up into the Pacific, while Australia settles itself nicely into the Atlantic, is really qite impressive.

It is possible that it's merely coincidental, but I do wonder if there is some physical effect to do with plate tectonics, gravity, or something of that ilk which actually does militate against antipodean land?
del_c
Jan. 9th, 2010 11:21 pm (UTC)
I wonder if you're being misled by the projection of the sphere on to a rectangle, into thinking the land has stretched "right round" the globe longitudinally, when it hasn't? The apparent stretch of west to east is actually quite a compact land mass, when seen from above and not from the side. The closest thing to stretched right round the former Pangaea has achieved is in the axis of its South American/Antarctic and Australasian extremities, not in the east-west axis. Apart from those two extremities, the globe divides neatly into a land hemisphere and a water hemisphere.

Admittedly, the fact that the stretched extremity of Australasia hits the narrow Atlantic in its bulk component, Australia, while only the Indonesian islands end up on the Amazonian bulk of America, is a bit of bad luck, but it's only bad luck. The lack of antipodal land that you're struggling to explain by physical means is just simple spherical statistics, no physics involved.
[edited to add my mashup of the two hemispheres]


Edited at 2010-01-09 11:48 pm (UTC)
nwhyte
Jan. 10th, 2010 10:22 am (UTC)
Pondering this: if the 29% of land was distributed randomly across the globe, then you would have 29% of 29%, ie 8.4% of the earth's surface would be land with land antipodes.

It's obviously a lot less than that (that would be almost exactly the combined area of the Americas).

That wikipedia link says that 7/8 of the land - ie 25.4% of the earth's surface - is in the 'land hemisphere', and the rest - ie 3.6% of the earth's surface - is in the 'ocean hemisphere'. If those were randomly distributed within their respective hemispheres, then the land with land antipodes would be 2*25.4%*3.6% = 1.8% of the earth's surface, roughly the area of China or the USA. I haven't calculated from the map (which would be rather tricky anyway) but I think that is about right, or if anything the real ficure is slightly more than that calculation would suggest.
applez
Jan. 10th, 2010 07:23 am (UTC)
For Sale
One partially-dug hole "to China"

Accepting bids now.
( 6 comments — Leave a comment )

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