Ground-penetrating radar could help archaeologists spot otherwise
invisible ancient footprints, suggests a recent experiment at White
Sands National Monument, New Mexico. Tracks left behind in layers of hardened mud and sand at the site record where humans crossed paths with giant sloths
and mammoths during the last Ice Age. But some of the tracks appear
only when conditions are just right—usually after a rain—which makes
them difficult to study. Archaeologist Thomas Urban of Cornell
University and his colleagues used ground-penetrating radar to spot
these so-called ghost tracks. The radar images also revealed layers of
compressed sediment beneath mammoth tracks, which could reveal
information about how the now-extinct woolly giants strode across the
Pleistocene world.
Invisible ink
To test the method, Urban and his colleagues pulled a radar antenna
across the pale gypsum sands of the former lakeshore, pacing out a grid
pattern over a site where, 12,000 years ago, a human and a mammoth
crossed paths. Excavations at the site had already revealed “ghost
prints” left by a person who walked north, and then back south, for
about 800 meters (2,625 feet). Sometime in the past, the prints filled with sediment and then got
covered by a layer of fine gypsum sand, so they’re usually invisible
from the surface. But the sediment filling the tracks holds more
moisture than the sediment around them, so when there’s just the right
amount of water present, the tracks stand out dark on the pale ground.
They appear and vanish again like a message written in invisible ink. Archaeologists already knew one location along the trackway had about
27 ghost prints. When Urban and his colleagues put their radar to the
test, the images revealed 26 of the prints—and the images were detailed
enough to calculate the length of the person’s stride and estimate their
stature. It turns out that the sediment filling the tracks also
reflects radar signals differently than the surrounding material, making
it possible to detect otherwise invisible tracks...MORE
Issues of concern to people who live in the west: property rights, water rights, endangered species, livestock grazing, energy production, wilderness and western agriculture. Plus a few items on western history, western literature and the sport of rodeo... Frank DuBois served as the NM Secretary of Agriculture from 1988 to 2003. DuBois is a former legislative assistant to a U.S. Senator, a Deputy Assistant Secretary of Interior, and is the founder of the DuBois Rodeo Scholarship.
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