THE GHOST BENEATH
THE WILD WEST
FROM TOP: KARIN SIGLOCH/UNIV. OF MUNICH (LMU); PE TE MCBRIDE/GE T T Y IMAGES
Today the crust is composed of eight major
tectonic plates—the vast, irregular slabs of rock
whose movements shift continents and sculpt
mountains. One hundred fifty million years ago,
the Farallon Plate covered more than one-third
of the earth’s surface. But at a rate of about
an inch a year, the plate plunged beneath the
western edge of North America, down into the
mantle. The seismic image above, created by
geophysicist Karin Sigloch of Ludwig-Maximil-ians University of Munich and based on data
collected by EarthScope seismometers, depicts
where the remains of that plate lie now. Color-coded layers represent depth intervals of about
120 miles; at its deepest, the plate is 1,000
miles underground. Sigloch’s study bolsters
the theory that the Farallon Plate ground
against the underside of North America and
drove up the ranges of the Rockies, including the Elk Mountains in Colorado, shown at
right. “By studying images of this plate deep
underground,” Sigloch says, “we can learn
about conditions at the surface tens of millions
of years ago.”
