The right images
bring abstract ideas to life.
On May 19,
I accompanied some geologists to Pinewood Lake west of Loveland, Colorado.
Sporadic rain and chill air dulled the greens of spring growth. Normally blue
skies were slate gray. At one point we detoured off the dirt trail, traversed a
meadow, and made a U-turn hook that forced us to climb down a couple of feet of
exposed vertical slabs of rock. We had just crossed what geologists refer to as
the “Great Uncomformity.” Above an extension of the vertical rock strata lay
many layers of red, pebble strewn, compressed soils from a time on our planet
when dragonflies the size of pigeons darted between alien, green-trunked trees
soaring skyward to bottle brush tops covered in spores.
In
geologist’s terms, uncomformities are places where layers of rock come together
that are very different in age, as measured by radioactive dating techniques or
recognized stratigraphy. Angular uncomformities are such junctures where the
layers are at odd angles to one another—sometimes as much as 90 degrees. When
geologists see this, the image can strike them a mental blow because of what it
implies: stretches of time laid bare that are so vast as to shatter human
comprehension.
James
Hutton (1726-1797) saw such a feature in England. It consolidated in a flash
what he already suspected: that the Earth was a tremendously old planet—much
older than what Biblical scholars proposed. He went on to write a two-volume
work, Theory of the Earth, which
crystalized this conclusion for others. (I write about this in more detail in
my book, The Restless Earth: Fossils,
Chelsea House, 2009.)
The
following information helps make the image of rock layers lying at right angles
to one another so powerful. The oldest of the vertically oriented rocks at this
site can be dated at 1770 to 1670 million years old (1.7 billion years). This
age predates all life more complicated than single cells. The vertical rocks
were originally deposited as ocean sediments at a time when dry land was a
sterile desert. Over time, they were crushed to rock; then partially melted.
Imagine the vast stretches of time to form layered muds and sandstones
accumulating millimeter by millimeter, and then imagine the additional eons
necessary to compress everything to a semi-molten sludge. And THEN imagine the
slow heave of forces that twists everything upright: old ocean beds stood on
end.
But that’s
only part of it.
Imagine the
forces of wind, water, and time scouring a billion years away to dust, carrying
it somewhere else to settle. Then a new, slow cycle of deposition begins—piling
up 300 million years of forests and dragonfly wings—until the dinosaurs die and
mammals build their empires on the ashes left behind.
Now, two
temporal dynasties of dirt lie at right angles to each other, with a monumental
gap eroded to oblivion between them. THAT is the Great Unconformity. That is
what humbled Hutton and every geologist since. They become mesmerized by
temporal vistas exposed at the intersection of angled eternities.
The Great Unconformity. Photo by Herb Saperstone
