The History of Geology


[ Birds chirping ] [Katelyn Salem:] “If you don’t know history,
then you don’t know anything. You are a leaf that doesn’t know
it is part of a tree.” This quote is from one of the greatest philosophers
of ancient history…Michael Crichton. And I think it does a good job of explaining why we’re about to take
the two most boring school subjects, history and geology,
and squish them together. With that, let’s start
where every great story starts, [ Angelic ahhs ]
the Bible. Actually, people were writing about
geology long before the Bible.
[ Banjo music plays in the background ] In the 4th century BCE, Aristotle hypothesized
that the Earth changed very slowly. Slowly enough that it couldn’t be observed
during a single lifetime. Aristotle’s successor, Theophrastus, later
wrote a book following Aristotle’s theories called “On Stones,” in which he described, among other things,
[ Lighter sparks up ] how various rocks and gems [ Fire roars quietly ]
reacted when heated up. In the 1st century CE, Pliny The Elder wrote
what might be considered the first encyclopedia set,
called “Natural History.” In books 36 and 37, he describes
a number of minerals and gems, and even details a hardness test
for telling fake gems from real ones depending on whether they can
be scratched with a steel file or not. People may have been studying rocks for much of recorded history
[ Angelic ahhs ] but for the history of modern geology,
we need to start with the Bible. [ Waves crash ] In the book of Genesis,
the Bible describes a great flood, which God uses to reset creation,
ridding the world of evil men, and allowing a select few moral
and just humans to repopulate the Earth. By the 1600s, the prevailing theory
was that proof of the great flood could be found
in the Earth’s strata. Strata are the Earth’s distinct layers of
rock or soil. Like, this one might be all granite,
while this one might be sandstone. But the Biblical story didn’t fit
with the theories of some. In 1666, Danish anatomist Nicolas Steno
was dissecting a shark. He noticed that the shark’s triangular teeth
resembled things known as “tongue stones,” which were sometimes found embedded
in rocky formations. [ Dragon roars ]
People believed these stones to be the petrified tongues
of dragons or snakes. And actually, our old friend,
Pliny the Elder, 16 centuries earlier, thought the stones fell from the sky
during lunar eclipses. [ Soft, echoey chanting ] But Steno instead thought, “If tongue stones look an awful lot
like these shark teeth… maybe they ARE shark teeth!” He believed that maybe, over time, the actual
structure of the shark’s teeth was replaced by minerals, keeping the teeth in the
original triangular shape. But then, how were the teeth
getting embedded into rocks? [ Rocks clack against each other ] Steno wondered if perhaps dirt and minerals
in bodies of water would settle to the bottom
to form horizontal layers over time. [ Squirtle squeaks ]
New layers would form on top of old layers, trapping whatever remained underneath. To test his theory, he began studying cliffs
in Italy, which led him to formulate three basic principles
which geologists still use today. The first is The Principle of Superposition. This explains that if a sequence of rock
has been undisturbed, the oldest layer will be on the bottom,
and the youngest layer will be on top. Easy peasy. The second is The Principle of Original Horizontality. This explains that all strata form horizontally. It’s worth noting that we’ve since
discovered minor exceptions, such as the way sand accumulates
on sand dunes. Thanks to gravity, deposits generally don’t [ Blow dryer turns on ]
form slopes greater than 45 degrees. We can use this principle to conclude that
these layers, of Bow Fiddle Rock in Scotland, were probably tilted by an earthquake
or uplift or…some other force. The third principle is
The Principle of Original Lateral Continuity, or TPOOLC, for short. [Dwayne:] Ahem. [Katelyn:] (Dejectedly) Yeah, you’re right. No one calls it that. Anyway… The Principle of Original Lateral Continuity
explains that strata form as unbroken, continuous layers of rock
that will eventually thin out to nothing, or end at the edges of a basin
if they happen to be filling one. Strata that are no longer connected
must have been fractured by a force, or separated by erosion, like you can clearly see
at the Grand Canyon in Arizona. Using these three principles,
we can understand the relationships between a rock layer’s age
and its position in the rock record. The study of that relationship
is known as stratigraphy. Now, with Steno’s contributions to
our understanding of stratigraphy, he’s sometimes thought of
as “The Father of Geology,” or sometimes “The Father of Paleontology,”
for his revelations about fossils. However, most people consider
the “The Father of Geology” to be a Scottish farmer of the 18th century
by the name of James Hutton. In 1788, Hutton visited Siccar Point,
where he found nearly vertical layers of greywacke, covered with horizontal layers of red sandstone. He reasoned that the only way
something like this could have happened was over a huge length of time,
[ Rock scrapes ] allowing the grey rock to be tilted or eroded
[ Sand clatters ] before the red rock settled on top. Hutton thought these layers in the ground
came from “materials furnished from the ruins of former
continents” and that, every day, the same processes that
are eroding away large bodies of rock are also building
up mountains. He called this process The Great Geological Cycle,
[ Angelic ahhs ] and hypothesized that it had been happening
endlessly, forever. Unfortunately Hutton’s theory
wasn’t made popular until after his death, when Charles Lyell published
the book “Principles of Geology.” His theory originally became known
as uniformitarianism, an alternative to the Bible’s theory of catastrophism, where the Earth was formed by catastrophes
like the flood. It followed the notion that the same geological
processes that are happening now probably happened the same way in the past. Thus, we can figure out what happened then
by looking at things now. The name uniformitarianism eventually fell
out of favor, since, you know, almost nothing about the
Earth is uniform. The term actualism was taken up instead,
[ A harp is strummed ] since geologic time can be explained
through actual processes that actually happen. Actualism has had a huge impact on science, extending even beyond the reaches of geology. [ Low, slow motion impact ] Charles Darwin himself used the concept of
actualism to understand that, much like the Earth, life itself was also changing slowly over
time. [ Tribal music swells ] Without a developed understanding of geology,
Darwin could not have written “On The Origin of Species.” Speaking of “origins,” I hope you’ll join
us next time, as we explore the origin of… well… everything! [ Fiddle music ] [ Birds chirping ]

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