[Rockhounds] Does The Great Unconformity equal Snowball Earth?

[Kreigh Tomaszewski]

When the famed explorer John Wesley Powell
<https://www.usgs.gov/staff-profiles/john-wesley-powell?qt-staff_profile_science_products=3#qt-staff_profile_science_products>
bumped,
splashed and thrashed his way down the Colorado River in 1869, he
discovered one of the most striking geologic features on Earth. Not the
Grand Canyon — although that too is a marvel — but a conspicuous boundary
between the sunset-colored sediments of the upper walls and the dark,
jagged rocks below them.

Powell had learned to read the layers of desert rocks like pages in a book,
and he recognized that the boundary represented a missing chapter in
Earth’s geological history. Later, researchers realized it was more like an
entire lost volume, spanning roughly one-fifth of Earth’s existence, and
that a similar gap existed in many places around the world.

“There must have been some sort of special event in Earth’s history that
led to widespread erosion,” said Steve Marshak
<https://www.geology.illinois.edu/people/smarshak/>, a geologist at the
University of Illinois at Urbana-Champaign who studies what has come to be
known as the Great Unconformity.

New research <https://www.pnas.org/cgi/doi/10.1073/pnas.1804350116> suggests
it was something special indeed. Scientists propose that several freak
episodes of global glaciation scoured away miles of continental crust,
obliterating a billion years of geologic history in the process.


https://www.latimes.com/science/sciencenow/la-sci-sn-snowball-earth-geology-20190103-story.html