The recent History Channel special "Life After People" examined the
physical mechanisms by which human civilization -- specifically, 20cen
architecture -- would decay after our sudden vanishment. It did not
address what non-architectural remnants would *persist* for future
civilizations to discover, or structures specifically *designed* to
survive.
<http://www.history.com/minisites/life_after_people>
ObSF, one of the talking heads was David Brin.
SUMMARY
The described failure modes include things that a non-specialist
wouldn't think of. For instance, salt crystals (such as sulfates
deposited by rainwater) growing inside concrete; moisture infiltrating
reinforced concrete and rusting the rebar, causing it to expand;
windows shattering when the seals grow old, and no longer compensate
for thermal movement in the metal frame; copper lightning rods
corrode. Plus such things as plants, termites, and mussels clogging
the cooling-water intakes of Hoover Dam.
Many things collapse because they were designed for regular human
maintenance. Protective paint on steel; pumps for tunnels that lie
below the water table. The same can be said of living organic beings,
of course.
We conveniently have an example of "post-occupancy city" in the form
of the area around Chernobyl.
Once the skyscrapers of Manhattan collapse, they'll become new
vegetation-covered hills. The narrator didn't specifically say so,
but the implication is that the rubble piles are so massive that it'd
take X decamillenia for ordinary agents to erode them.
Wooden houses collapse, due largely to the depredations of termites.
The narrative didn't address things that would survive *inside* the
houses, which I expect would include: granite countertops, stone and
ceramic tile, ceramic bathroom fixtures; and on a shorter time scale,
plastic plumbing and stainless-steel cookware. Obviously toilet
manufacturers should start molding humanity's great literature onto
the unused undersides of commodes. :)
In a one-story with no cellar, these artifacts would stay basically
where they were put (short of bears shoving them around). A two-story
would have a jumble of fallen second-story plumbing. A house that
collapses into its own cellar might make a better archeological site,
since it would soon fill with silt.
IN SCIENCE FICTION
ObSF, human explorers often encounter alien artifacts that have
withstood untold ages. How? Either they're so huge that the elements
can't wear them down, they're built somewhere that doesn't *have*
erosion, they're composed of astonishingly strong materials, or
they're self-maintaining.
(The Stargate team sometimes encounter gates that have succumbed to
erosion or volcanic eruption, but usually they're sitting unencumbered
the middle of a meadow, the foundation perfectly level. In the
Pegasus galaxy, most of the gates are still in use, but back home
they're usually forgotten relics on abandoned Goa'uld colonies.)
If we were actually interested in building maintenance-free structures
that last a long, long time, and cost was no object, what would we
use? Stainless steel? Diamond slabs? Would it work to simply coat
steel and concrete with impermeable diamond instead of paint? As an
unmatched thermal conductor, is diamond immune to destructive thermal
stresses? Would it be safe fom everything short of volcanic bombs and
crowds with hammerS?
SEE ALSO
_Motel of the Mysteries_, 1979, David Macauley.
<http://www.amazon.com/Motel-Mysteries-David-Macaulay/dp/0395284252>
Yucca Mountain nuclear waste repository
<http://www.ocrwm.doe.gov/>
The Long Now Foundation
<http://www.longnow.org/>
The Svalbard Global Seed Vault
<http://en.wikipedia.org/wiki/Svalbard_Global_Seed_Vault>
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