Hey folks, Dr. Chapman here. Today we're
going to talk about Canyonlands National
Park and connections to salt, nuclear weapons, and the age and composition of the Earth.
Canyonlands National Park is one of the
many parks and monuments on the Colorado Plateau.
It's located at the confluence
of the Green River and the Colorado River.
The park contains many spires and
and buttes and canyons, but it also
contains a very curious feature called
Upheaval Dome. For decades scientists
have debated what created this feature
and there's two main hypotheses.
The first one is a salt diapir and the
second one is an impact structure.
Salt has a very low density relative to other types of rocks and if salt becomes
buried beneath heavier and denser layers
of rocks, it can actually start to flow or
maybe even rise up through the layers of
rocks like a blob pushing its way up
through a lava lamp.  This blob type
structure we call a diapir. It can be
made out of salt or magma or any other
type of material. In physics we call
diapirs Rayleigh Taylor instabilities
because having a low density layer
beneath a layer of higher density
material creates a density instability.
Salt diapirs are not uncommon and in
some places on Earth they're just
everywhere like the Gulf of Mexico where
salt diapers are a common exploration
target for oil and gas where the oil and
gas becomes trapped on the margins of
the diapirs.  Salt diapirs are common
in the Canyonlands National Park area
too. There's a thick layer of salt that
formed from the evaporation of an
ancient inland sea about 300 million
years ago in the Pennsylvanian period.
The salt layer is called the Paradox
Formation. In Cataract Canyon, within
Canyonlands National Park, the Colorado River has eroded down deep enough to actually
intersect this salt layer and it's
dissolving the salt in the river water
and excavating it and carrying it away.
Where the salt has been excavated the
rocks overlying that salt have collapsed
and dropped down and there's a feature
within Canyonlands National Park called
the Grabens.
Graben is actually a geology word
referring to a
block of rock that has dropped down
between two extensional faults or normal
faults. One of the criticisms of the salt diapir
model for Upheaval Dome is because no
salt has been found in the core of the
dome structure. One possibility is that
a salt diapir passed through this area
and continued up to the surface and just
left no salt behind. But other scientists
are skeptical. The alternative hypothesis
for the origin of Upheaval Dome is an
impact structure. For many years the main evidence supporting this idea was just
the shape of upheaval dome. But in 2008
the hypothesis got a big boost with the
discovery of shocked quartz and shistovite.  Shocked quartz is a type of
quartz that forms under high pressure
and it was originally discovered during
nuclear bomb testing. Shistovite is a
high-pressure polymorph of quartz.
Polymorph sounds like some sort of
sci-fi alien race, but just describes a
mineral with the same chemical
composition but the atoms are arranged
in a slightly different manner.
The polymorph most people are familiar
with is diamond. Diamond is a polymorph of graphite. Both are made of carbon,
but in diamond the carbon atoms are
packed more closely together just like
in shistovite, the silicon and oxygen
atoms are packed more closely together.
Shistovite was first discovered at
Meteor Crater in Arizona. Meteor Crater
is not a national park or monument, it's
privately owned, but you can still go
visit it. Meteor Crater is kind of square-ish
shaped. We're not exactly sure why it has
a square shape, but geoscientists have hypothesized it has to do with fractures
and joint patterns within the
surrounding rock. Geologists estimate
that meteor crater formed 50,000 years
ago from the impact of a 50 meter wide
meteorite. Most of this meteorite
vaporized on impact but it did leave
some fragments behind and these
fragments have been studied for over a
century. Meteorites hitting the earth
might seem like a rare occurrence, but
it's happening all the time. Every day
over a hundred thousand kilograms of
mass is added to the earth by the
addition of space dust and small meteors
hitting the planet. Meteor strikes were
much more
in the early history of the earth and
the earth actually formed by the
clumping and accretion of space dust
into clouds and rotating disks and then
planetesimals and then finally planets
but they're all essentially made of the
same thing that meteors are made from and meteorites are made from.
So meteorites actually tell us the
composition of the Earth and tell us
what the earth is made of. If we could
take the entire Earth, grind it up, stick
it into a blender mix it up, and analyze
it  - we'd have the composition of a
meteorite. Meteorites come in three main
flavors or types. The first type is
called chondrites it's what I just
described a mishmash of the entire Earth
as a whole and is a snapshot of the very
early Earth when all the elements were
still jumbled up. In fancy geochemical
diagrams you'll often see data plotted
relative to chondrites, which is a way of
plotting something relative to the
composition of the entire Earth. The
other meteorite flavors are rocky
meteorites and iron meteorites which form from the differentiation of chondrites.
Differentiation is what happens when you
leave a bottle of salad dressing too
long in the bottom of your refrigerator.
The lighter oil rises to the surface and
the heavier vinegar falls to the bottom.
So these two substances differentiate
from one another. Differentiation is how
the layers of the Earth formed. Denser
elements like iron and nickel sank
towards the center of the Earth and
formed the Earth's metallic core. Less
dense elements started to rise to the
top and formed the rocky mantle and
eventually the crust. The least dense
elements became the atmosphere. The
meteorite that formed Meteor Crater in
Arizona was an iron nickel meteorite and
is most similar in composition to the
Earth's core. And you can buy pieces of
it on the internet. Before the internet
existed, a geoscientist named Clair
Patterson in the 1950s analyzed pieces
of the Arizona meteorite, at that time
called the Canyon Diablo meteorite, and
he used them to calculate the age of the
Earth to be 4.5 billion years old. A
number that has remained more or less
unchanged
ever since. Hey thanks for watching, check out some more videos and share them with
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Take care.
