Good day everyone. This is Professor Rood and I will be lecturing on chapter one
today;
An Introduction to Physical Geology
So what is geology?  It is the science
that studies the earth, and there are two
main branches; physical and historical
geology. This course focuses on physical
geology which encompasses studying
Earth's materials as well as the
processes occurring at Earth's surface
and within Earth, what we call
external and internal processes.  If we
look at examples of external processes,
we can look at this picture here and
what we see is that water is running
down the Grand Canyon and eroding rock
away. That is an external process. In this
image we are seeing lava being erupted
out of a volcano, Mount Etna. Now this lava
formed deep within the earth so rock
melts, magma forms, deep within the earth
In this case it was later erupted at the
Earth's surface, in which case we call it
lava. Historical geology is the other
main branch within geology and we look
at the evolution of Earth overall as far
as evolution of life as well as
evolution of events, geologic events, such
as when mountain ranges were formed,
where lithospheric plates were located
at various times in the past.
So the earth can pose some issues for
people.  We have what are called natural
hazards such as volcanic eruptions,
floods, tsunamis, earthquakes and
landslides. Now these natural processes
become hazardous when people live in
these areas where these events occur.  Here is a picture of Japan, and what is
happening here after the great
earthquake, a tsunami formed and rushed
onto the land, and in fact, most of the
damage in this case was not from the
ground shaking but from the tsunami that
was generated as a result of an
earthquake out in the ocean. Another important aspect of geology are the resources that
come from Earth. Everything that we have
in front of us has been extracted from
the earth. We drink water from the earth;
soil, we use soil for growing various
crops. We mine minerals, and we get a lot
of energy from the earth, such as fossil
fuels; coal and oil for example. A little
bit of history here. In the mid sixteen
hundreds James Ussher was an arch bishop
and his thought was that the earth was
approximately 4,000 years old.  So all of
the landscape that he saw on earth he
thought had to have happened very
rapidly due to the young age of the
earth in his view.  This idea is called
catastrophism.  Later on, 1795, James Hutton,
known as the father of modern geology,
developed a concept called
Uniformitarianism. Uniformitarianism is
often stated as "the present is the key
to the
past," and what that means is that
processes that are operating at the
Earth's surface today and forming
different landscapes for instance also
are the same processes that operated in
the geologic past. Looking at a picture
of the Grand Canyon, we have more than
one and a half billion years of Earth
history represented in this area. At the
very bottom are two billion-year-old
rocks, the vishnu schist, and the uppermost
layer is 270 million years old. The rest
of the material that is younger than 270
million years old has been removed
through erosion. So if we accept
uniformitarianism as an explanation of
what we see and the processes operating
at the Earth's surface, then we accept
that the earth is very old, much older
than 4,000 years, and in fact, has been
determined to be 4.56 billion years old.
That's what we call a great time, or
immense time, or deep time. This is an
image of the geologic time scale and
what I want to point out here are how we
divide up time in geology. So the
largest amount of time is what we call
an eon.
There are four eons; the Phanerozoic,  the
Proterozoic, the Archean, and the Hadean. These 3 eons here, the Hadean, Archean and Proterozoic
are commonly lumped
together and referred to as the
Precambrian.  So eons represent the
greatest amount of time.  Eons can be
subdivided into smaller time units
called Eras.  The three Eras of the
Phanerozoic are the Cenozoic, Mesozoic,
and Paleozoic. Now these Eras have a
certain meaning if we can take apart
what the prefix to the word is. Paleo
means ancient. "zoo" is life. So Paleozoic
is ancient life. That is the era of
ancient life. Mesozoic, "meso" being middle,
is middle life, and then finally Cenozoic, "ceno" means recent
So this is the era of
recent life.  Eras can be subdivided
into Periods, and so this the whole list
of different periods. Most of us
have heard of the Jurassic because of
movie Jurassic Park, but all these names
have a history behind them that
we will look at more closely in our
geologic time chapter. The numbers here
that are represented, are in millions of
years. So this tells you what the time
constraint is for a certain period or
era or eon.
And last, periods can be subdivided into
epochs, and epochs just for the Cenozoic era
are shown here. So summarizing, eons
represent the greatest amount of time
followed by eras, periods, and then epochs
are the smallest.
So the next section that we're going to
discuss is the scientific method
and that will be introduced in our next
video
