All right, let's get started with some science. Geography is the study of the Earth, the
whole Earth and everything related to it: our relationship to space,
the rest of the solar system, climate, rocks, vegetation, animals, people. Where people are concerned,
we get into more detail: where people are, their culture, their politics. This is a huge topic. It is so huge — well, it does cover
everything about our planet — it is so huge that institutions, textbook authors,
everybody, divide it into two halves. Half of this dealing with
the physical environment, we call physical geography; the half
dealing with humans we call human geography. This pie chart from Chapter 1 in your textbook
shows this split. Here in the middle is geography, the environmental half, and the people
half; human geography, physical geography. As we move out from the center we come into
the various subdivisions of physical geography up here: mathematical geography, climatology,
geomorphology, biogeography, soils geography. And of human geography down here:
social geography, economic, historical, cultural, and political geography.
As we move outwards towards the edge, these subdivisions of geography resolve
themselves all the way into specific disciplines of their own, a number of which are subjects that
you can take here at Long Beach City College. Astronomy, for example, is
a discipline we have here, geology, biology. Pedology, no. And similarly in
the human half, out here we come to sociology, economics, history, anthropology, and poli sci. So geography, and the halves of geography:
physical and human geography, are generalizing subjects. Out here we are less generalizing,
we're going into more depth and detail on specific topics. This class is Physical Geography,
so we concern ourselves with this half of the pie. We also have classes here at City College
that address that half of the pie there. We don't call them human geography at Long
Beach City, we just call these classes geography, and these ones we call physical geography, and that's where you'll find them
listed in the Schedule of Classes. So Physical Geography — which is what we're studying —
deals with the processes and features that make the Earth's
physical surface the way that it is. Detailed specialties within
Physical Geography include: Meteorology — this one's probably the
most misleadingly named science there is. What do you think meteorology is all
about? Meteors, other space rocks? It isn't. Meteorology is the weather. Climatology, obviously, is climate. How,
how weather and climate are the same and how they differ is something we'll be talking
about in detail as soon as we hit Chapter 4. Geomorphology — this is a bit of a mouthful.
Whenever you come to a big multi-syllable word like this, the way to handle it is to break
it down: geo=Earth, morph=shape, ology=study. Earth-shape-study. Geomorphology deals with,
literally, the shape, the features, of the Earth. Hills, valleys, mountains, canyons and so on. Biogeography is pretty obvious:
bio=life, geography of living organisms. Soil science — can't get much simpler
than that: understanding the soil. Hydrology — what does that deal with?
Well, hydr=water. Now you might think that hydrology would deal with all the water on
the Earth, but there's so much water in the ocean that we separate off the ocean
and make it a topic of its own. And what about this one? We separate off ice. Ice
sheets and glaciers. So what's left for hydrology? Basically fresh water: water
that you might consider drinking, and indeed hydrologists are much in demand: they are scientists who work for water
companies, water utilities, all over the world. How do we go about studying Physical Geography?
Well, Physical Geography is often described as the spatial science — spatial: s-p-a-t-i-a-l
— because it deals with space, area, where things are, and so we have a
series of themes in Physical Geography. These begin with location: how do you locate
yourself on planet Earth? And once you've done so, how do you specify that location? Much of Chapter
2 in the textbook deals with this issue. Once you're able to specify locations, we move on to
characteristics of places. What is it like at a particular place on Earth? And once we understand
the characteristics of a bunch of places, we can start to put together spatial distributions and
patterns. Where on planet Earth is the rainforest, for example? Then we move up to more
complex, and less well understood themes. Spatial interactions. Let's see,
for example, the El Niño phenomenon — which I'm sure you've heard of — involves
ocean currents in the southern Pacific. How does that influence weather in North America
and other places around the world? — spatial interactions. And the last major theme is Earth
changes: how does the Earth change over time? There are big dramatic changes, like volcanic
eruptions, ice ages; there are small scale, more subtle changes, like a river gradually
changing its course, as it erodes its banks. We used just to have to worry
about nature's processes, causing changes to the Earth. Now we have
to add human-induced changes, such as, what is currently probably the biggest issue
on the planet: human-induced climate change, which is already affecting us, and will continue
to affect us all, more and more, in the future. Why would we want to study Earth? —
apart of course from to get a grade. Well Earth is where we live and so far, despite
some pretty intensive exploration efforts, Earth remains the only place
basically that we can live. So what part of Earth are we talking about?
If we're thinking about where we can live, are we interested in like the deep interior of
the planet? No, we're interested in basically the surface, more or less. Hence the subtitle of this
class: Physical Geography — Earth Surface Study. To get an appreciation for the Earth's
surface, I'd like us to do a little comparison. Let's compare the surface of the
Earth with the surface of someplace else. Where else, other than planet Earth, have we
actually been to? — people, tramping around, studying. Well, that would be the Moon. So let's compare the Earth with the Moon, and look at some important features. First of all, rocks. Earth is composed of rocks. Is
the Moon composed of rocks? Yes, it is. And you know, after we spent an incredible amount
of money and effort sending people to the Moon, they picked up rocks from the Moon,
they brought them back with them, and what did we find? Basically, the rocks on
the Moon are the same as the rocks on the Earth. Well, why is that? Rocks are made of minerals, and we have exactly the same minerals on the
Moon that we do on Earth. Minerals are the natural compounds that common elements
make when they chemically bond together, and when they bond together they make the
same kind of things wherever they are. So same minerals lead to the same rocks. Where the rocks of the Earth
appear at the surface, they form landforms: hills, valleys,
mountains, plains, canyons, cliffs, beaches. We have a wealth
of landforms here on Earth. Do we have landforms on the Moon? Yes, we do.
Are they the same landforms that we see on Earth? Well, not so much. What's the most prominent
landform that we see on the Moon? I think you'll all answer that one: craters. And what forms those craters?
Here on Earth, craters are common in the tops of volcanoes: they're the hole that stuff
erupts out of when the volcano blows its top. Is that the major reason for the craters on the
Moon? No, it's not. The craters on the Moon are what we call impact craters: they're formed when
something — a rock coming from space — slams into the surface and throws
rock out in all directions. Do we have impact craters like
that here on planet Earth? Yes, we do. How common are
they? Well, they're not. You can probably think up three or four that you know about, maybe. Geologists know of a couple of dozen or so. What about the Moon? It's covered in them
— thousands of them. Why the difference? I wish I could ask you this
question to your faces, and discuss your answers with you,
but in the circumstances we can't. However, a very popular response to that
question is this: "The Earth's atmosphere burns them up." Hollywood movies, unfortunately,
have given us all seriously the wrong idea. You know those disaster movies: let's see, there's
"Armageddon", where Bruce Willis saves the planet, and around the same time there was "Deep Impact", where nobody saves the planet,
it gets creamed at the end. These movies involve this rock coming
towards us, and through the two-hour movie, every now and again the camera looks
up there and there's that rock. It's gradually getting bigger and bigger
and bigger, flaming its way towards us. Why is it flaming? Well
it's hot, it's burning up — which is what happens in the atmosphere.
Now, that rock is traveling at a speed of somewhere around 20,000 miles an hour.
The atmosphere is about 10 miles thick. At 20,000 miles an hour, how long does it
take to travel through 10 miles of atmosphere? Well, blink and you missed it, right? So should the rock be flaming towards us
for two hours in the movie? Of course not! Totally absurd! Doesn't stop Hollywood from
doing it. Looks good. Even this image here, from a reputable weekly news magazine, is
equally absurd. The atmosphere is that thin blue fuzz next to the planet, and way out there
in space, here's this rock flaming its way along. Ridiculous. Yeah, your incoming rock spends
maybe a second or two in the atmosphere. How much rock can you melt — vaporize —
burn off in that time? Not a whole lot. What that means is that little itty
bitty rocks — pebbles, sand grains — it's tiny things. They burn up completely,
yes, vaporized in the atmosphere. Anything bigger than that is going to hit
the ground. It'll be melted around the edges, but it's going to hit the
ground. So, in other words, things that are so small that they couldn't make
a crater do burn up in the Earth's atmosphere. Anything that's big enough to make any
kind of hole in the ground does just that. Yes, it's more complicated than
that: some of the big ones, as they're coming in, explode, and
land as a bunch of smaller fragments. There was that famous example
over Russia, just a few years ago. The explosion gave off roughly
the energy of an atomic bomb, and damaged roofs, windows, and
buildings, for I think 100 miles or more. A chunk of it crashed into this frozen lake,
blowing a large hole in the ice. Divers went in and retrieved a big chunk of the meteorite
itself. if you're interested in pursuing this topic further, you'll find, right after
this video ends, I've placed an optional link to one of the many Youtube videos showing what
it actually looked like, as it was happening. But basically, anything that's big enough to hit
the ground is going to do so. So forget that one. Another proposal I've heard is: "Well, the Earth
has more gravity than the Moon." Obviously it does, it's bigger. More gravity ought to
pull in more objects: that ought to mean that the Earth gets hit more than the Moon,
not less. So that argument doesn't work. Then there's — oh yeah, it's a good one —
"three-quarters of the earth is covered in ocean, so you wouldn't see craters there." Fair
enough. Is that . . . is the argument here, that all the incoming rocks from space
aim for the ocean and avoid the land? Because if they hit randomly, there still
should be lots and lots of craters on land. None of these arguments work. So what is the real scoop? Let's take a look
at some of the real craters here on Earth, and talk about them.