This is a follow-up to the threads in early Feb08 about the History
Channel's "Life After People" special, and the similar one by National
Geographic shortly after. The programs examined how quickly ordinary
human structures (of wood, steel, and concrete) would last if not
maintained. But it only looked at things *exposed to the elements*.
What about structures underground?
Consider the gold vault of the Federal Reserve Bank of New York.
It's 80 feet below street level (but also 50 feet below sea level,
which may mean it's vulnerable to flooding), and rests on Manhattan's
bedrock because it's so heavy. How heavy? It contains around 8000
tons of gold. The three-story bunker is made of steel-reinforced
concrete. The entrance is a 90-ton steel cylinder (airtight and
watertight when closed) set in a 140-ton steel and concrete frame.
<http://www.newyorkfed.org/aboutthefed/index.html>
<http://www.newyorkfed.org/education/addpub/goldvaul.pdf>
Alien archeologists aren't going to notice underground vaults with a
visual survey -- but a gravimetric scan will certainly(?) find this
"mascon." Granite has a density of ~2.75 g/cc, steel ~7.8, and gold
19.3.
(Offhand, I'm not sure of the "resolution" of satellite-based doppler
gravimetry, or of the portable units used by geologists.)
And even if the vault *does* corrode, the gold won't. (Not a lot of
aqua regia in groundwater.) Finding neatly stacked square blocks of
gold, stamped with unintelligible but repeating symbols, would be a
good sign of intelligence.
And moreover, even after the vault (and all the other foundation
pilings in the city) *do* corrode, they'll still leave an atypical
elemental signature in the soil (at least until the site gets
resurfaced to a depth of 50 feet by mega-glaciers and vulcanism), if
the alien archeologists are the type to sift everything looking for
potsherds and bone fragments.
(And we can invert this situation: instead of one of those SF stories
where the human explorers find a largely-intact alien city of
cyclopean megaliths, they have to perform a painstaking search for
fragments and traces, probably starting around coasts and fossil river
deltas.)
Thoughts?
--
** Phillip Thorne ** pethorne@[EMAIL PROTECTED]
**************
* RPI CompSci 1998 *
** underbase.livejournal.com ***************************
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