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(Dean
Fikar/Moment/Getty Images) |
Few
geological puzzles are as confusing as the Grand Canyon's 'Great Unconformity'
puzzle: more than a billion years of missing rock layers that weren't deposited
and piled like the rest of the geological record for some reason. It's as if
those years didn't exist.
In 1869,
geologist John Wesley Powell was travelling down the Colorado River when he
discovered this unusual gap. We'd be able to date those layers later. Rocks
that are 1.4-1.8 billion years old exist close to rocks that are only 520
million years old in certain areas.
According
to geologist Barra Peak of the University of Colorado Boulder, there are
"wonderful lines." There are rocks that have been pressed together at
the bottom, which can be seen plainly. The layers are stacked vertically. Then
there's a cutoff, followed by these lovely horizontal layers that produce the
buttes and peaks that we identify with the Grand Canyon.
What
happened to the rest of the rocks?
According
to a new study, the Grand Canyon's geological history is more complex than
previously assumed, and that different areas of the site may have changed in
different ways over millennia, causing some rock and silt to be washed away to
the ocean.
According
to geologist Rebecca Flowers, also of the University of Colorado Boulder,
"we have new analytical technologies in our lab that allow us to decipher
the history in the missing window of time across the Great Unconformity."
This is
something we're undertaking at the Grand Canyon and other Great Unconformity
sites across North America.
Thermochronology,
which uses a series of chemical analysis techniques to quantify the heat stored
in rock when it was produced, is the foundation of these new methodologies. The
amount of heat emitted corresponds to the amount of pressure exerted on
geological formations.
The
researchers' findings show that the gaps in the geological record were caused
by a series of modest but substantial faulting episodes. These would have
occurred around 633 to 750 million years ago, during the cataclysmic breakup of
the supercontinent Rodinia, a chaotic period in Earth's tectonics that may have
prevented rock layers from settling in a more regular manner.
The
western half of the Grand Canyon has undergone significantly different geologic
contortions than the eastern half, which tourists are most familiar with,
according to samples gathered and evaluated by the researchers.
Peak
claims that there isn't a single block with the same temperature history.
Basement
rock, for example, appears to have come to the surface in the western half of
the canyon 700 million years ago; in the eastern half, the same layers of stone
are buried behind several kilometres of sediment.
The
discoveries aren't nearly enough to put an end to the Great Unconformity's
mystery, but they're a step in the right direction – and the researchers
believe the same techniques may be used at other sites in the United States
where comparable geologic contortions have been detected.
What is
undeniable is that the Grand Canyon continues to inspire awe, not just because
of its natural beauty, but also because of the way it depicts our planet's
geological history over billions of years.
According
to Peak, "there are just so many things there that aren't present anywhere
else." It's an incredible natural laboratory.
Read More
Here.
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