We are entering the era of geography, an era when geographical thinking is essential for
making sense of a globally interconnected world, a bold claim for a discipline that
is defined more by a perspective than by a particular topic.
But it's an integrated perspective that can help us understand everything from the movement
of the tiniest grain of sand, to the clashing of continents, to the rise and fall of nations,
to the trekking of hurricanes, to the distribution of material wealth across the globe.
I am Alec Murphy, and I'm going to show you how this much ignored subject in 20th century
America, rose to a position of prominence in the 21st century.
This is the story of physical geography, making sense of planet Earth.
In this fifth program, layering the planet, we will employ a geographic perspective to
look at Earth, not just as a sequence of layers from the inner core to the uppermost reaches
of the atmosphere, but as a set of layers that are coupled, always interacting with each other.
A classic story of the interaction of layers took place here at the John Day Fossil Bids
in Central Oregon.
During the Cenozoic era, known as the Age of Mammals and Flowering Plants, large and spectacular
volcanic eruptions took place.
They sent so much ash into the atmosphere that when it settled back down, it killed and
buried many plants and animals living in the area.
This opened the way for the arrival of new plants and animals, a new ecosystem formed.
As the volcanic action grew, it produced the Cascade mountain range, which cooled and
dried the climate to the east.
Eventually, the ash turned into sedimentary rock, rock seen today as these bad lands.
Rock that through the force of water is eroding away, producing new soil and reshaping the
landscape.
The event that triggered it all, massive volcanic eruptions, those eruptions were caused by plate
tectonics.
The movement of one of Earth's oceanic plates diving under the North American plate.
This example introduces all the major spheres studied by physical geographers.
The present day bad lands form part of the lithosphere.
The volcanic ash spews into the atmosphere.
The devastating impact of the volcanoes affected the biosphere.
The fallen ash became a new soil layer of the petosphere.
And the present day sedimentary layer is once again combining with plants and the hydrosphere
to modify the lithosphere and the petosphere.
And as I like to point out, humans are increasingly getting involved as well, altering the character
of all of these spheres.
So not only are these various spheres of the planet interacting today, but as we've just
seen, the interaction can take place on enormous timescales and over great distances.
Less than 200 years ago, it seemed obvious to most everyone that the surface of the planet
was one continuous layer, with bumps and dips of force, but still like a skin stretching
over the globe.
It was a layer that sometimes dropped down miles to the floor beneath the oceans.
That all changed with the discovery of plate tectonics.
With the discovery that the surface is actually carved up into a variety of massive plates,
some continental and others oceanic.
Furthermore, these plates are on the moon.
And we now know the Earth is made up of three main shells, the very thin brittle crust that
we're all familiar with, the mantle below the crust, and the core at the very center.
Although the core in the mantle are about equal in thickness, the core actually forms
only 15% of Earth's volume, whereas the mantle occupies 84%.
The crust makes up the remaining 1%.
A layer of rock, 5 to 25 miles thick.
It is primarily made up of igneous rock, such as these granites found in the Sierra Nabata's.
For every rock type, there is a process that produced it.
The origins of igneous rock lie below the hard and brittle crust.
Here temperatures are so great that minerals exist in a molten liquid state called magma.
When cracks appear in the crust, magma is forced upwards by internal pressures.
Igneous rocks are formed from magma, magma that very slowly cools, solidifies, and commonly
crystallizes within the crust.
Over time, erosion can expose some of these solidified igneous blocks.
Perhaps the most spectacular example of this process is Devil's Tower in Eastern Wyoming.
Of course, when magma is extruded onto the surface of the Earth, it cools more rapidly,
producing the volcanoes and lava fields that are found throughout the world.
The least common crustal rock type are sedimentary rocks.
Rocks that have been formed by the buildup of sediments and minerals layer upon layer
either in the ocean or on land, such as those found in the Badlands at John de Fossel beds.
The second most common rock type, making up the crust, is Metamorphic rock, which is
the most frequently found rock type in the Appalachian Mountains.
Sedimentary rocks become metamorphized when they are subjected to heat and pressure, usually
related to mountain building.
Metamorphized sandstone, silkstone, shale, and limestone are found throughout the Appalachian
mountain range.
And in places, their original sedimentary layering is clearly visible.
It is out of these three rock types that virtually every land formation has been shaped and formed
over time by a wide variety of forces, unvarying and time scales.
However, every landform visible on the planet today was created after the Great Extinction
Event that killed most dinosaurs 65 million years ago.
It is not surprising that the lithosphere has its greatest impact on the petosphere.
The surface layer commonly called soil, soil that is as dynamic as the shifting sands
of Northern Africa.
As the exposed crust breaks down, it can be ground into increasingly fine bits and interact
with the biosphere, mostly plants.
One of the results, soil.
A classic example of soil development is observable in this lava field.
We can see the process through a sequence of older and older rocks.
Starting with the most recent eruption, there is nothing but exposed lava.
Older eruptions over time begin to show some plant growth.
And the very oldest lava now has pockets of significant soil, which supports a variety
of plants.
Soil is the uppermost layer of the land's surface.
It's relatively loose, it's largely derived from the lithosphere, and it's what plants
depend on for nutrients, water and physical support.
Earth can contain a wide variety of matter, minerals, all kinds of rock types, organic
material living in dead, and water.
By the early 19th century, Earth scientists began to recognize that different combinations
of these factors were critical to agricultural production.
And perhaps even more importantly, soils had to be managed to enhance and maintain agricultural
productivity.
Soils, like every other geographical phenomenon, are constantly changing.
What are the soil types, and what is their distribution?
Dr. Patricia McDowell is an expert on soil types.
In the US, we classify soils into about 10 or 12 major soil orders, and each individual
type of soil is controlled by its environment.
What's the climate?
How much water is available, how cold or how hot is it?
That drives weathering, that drives biological processes in the soil.
What kind of vegetation grows on it?
And so, when we think about soils, there's a large range of distinct soil types ranging
from the spodasols of the conifer forests of northern North America and Asia to the mollasols,
the rich prairie soils of the Great Plains that developed under grasslands for thousands
of years, to the rittasols of desert areas where there's always a lot of evaporation.
That controls how minerals and other products, other chemical products are distributed through
the soil.
But as we have just seen, the production of soil is interconnected not only with the
lithosphere, but also with three of Earth's other spheres, the biosphere, life, animals,
plants, and microorganisms, the atmosphere and its associated climates, and the hydrosphere,
the dynamic movement of water.
It has been said that we live on a watery planet.
Indeed, over 70% of Earth's surface is covered by water.
While fresh water makes up less than 3% of the water in the world, its impact on Earth's
other geographical spheres is enormous.
Water is a major component of the atmosphere.
Along with temperature, defines the climates of the world.
Water is essential for all land plants and animals.
And to a large extent, it defines the life-carrying capacity and agricultural potential of all
the continents.
And water has enormous, erosional, and depositional potential.
In its solid state, in the form of glaciers, it carved the magnificent peaks of the Grand
Tetons and deposited the hilly drumlands in the Upper Midwest.
In its liquid state, it shaped the Grand Canyon, produced the delightful waterfalls of the
Appalachians.
And on a timescale of days, not millions or even thousands of years, historic flooding
took place in Nashville and Central Tennessee on the first two days of May 2010.
In 48 hours, over 13 inches of rain fell.
It turned the Swollen Cumberland River, a dark brown in color.
The torrential rains and the river were carrying away Tennessee's precious topsoil.
Topsoil that would eventually be deposited in the Delta of the Mississippi River.
This whole process of storms, flooding, rivers moving to the sea, is all part of the hydrologic
cycle.
The hydrologic cycle is a geographical model that describes the storage and movement of
water between the biosphere, atmosphere, lithosphere, and the hydrosphere.
Interestingly, ancient people seem to have understood, in a simplified way, how the hydrologic
cycle works.
It was written in one of the Old Testament's oldest books.
Let me quote from Job, chapter 36, verses 27 to 29.
For he draws up drops of water, which distill as rain from the mist, which the clouds drop
down and pour abundantly on man.
Indeed, can anyone understand the spreading of clouds, the thunder from his canopy?
No interaction between the planet's various spheres is more important to life and human
life in particular than the hydrological cycle.
The day starts with a bright blue sky.
By mid-afternoon, water is evaporating from the surrounding ground and lakes.
In the sky, clouds are forming.
Early evening, a thunderstorm starts.
Rain falls.
Water fills nearby streams.
This is the movement of water molecules, some of which will eventually reach the ocean.
There, some of those same water molecules will once again evaporate into the atmosphere,
and the process continues anew with the formation of new clouds.
Each year, 16 million events like this occurred, and at any given moment, 2,000 thunderstorms
are happening across the globe.
The water on our planet forms a closed system, that is, the same finite amount of water molecules
has been here for eons.
Scientists like to say that most of these water molecules are in storage.
99% are in oceans, lakes, and streams.
Locked up in glaciers are held in underground aquifers.
The remaining 1% is in the atmosphere.
Water is constantly circulating from one storage area to another through the hydrological cycle.
One way to view that thunderstorm is to recognize that not only is it transforming water from
one state to another, but it is transporting water from one place to another.
Over time, this cycle of evaporation and precipitation reaches a dynamic global balance.
This balance does not hold true for individual places, however.
In some places, such as deserts and oceans, evaporation generally exceeds precipitation.
So there are other places on the continents that get the extra portion of precipitation.
More or less precipitation dramatically affects the biosphere, the layer of life that extends
from the depths of the oceans to the upper reaches of the atmosphere's troposphere.
The biosphere is the part of the Earth that contains all life, and it's easy enough to
think of that in terms of the surface of the Earth, the layers where we see animals and
most of the vegetation and microbial life and so on.
But the biosphere goes far beyond the surface skin of the Earth.
There are not only flying things in the air, like birds, but microorganisms extend miles
up into the atmosphere.
At the same time, there are places on the Earth that contain biota that we wouldn't
even realize, for example, in the boiling springs of Yellowstone or deep within rocks.
Microbial life has been found hundreds of feet below the Earth, and perhaps more we really
don't know.
The ocean too is part of the biosphere.
If you look at the shallow seas of the world, that is an area rich with life where sunlight
can penetrate and drive biological processes.
But even at the deepest parts of the Earth, there are living things.
When they descend it down to the bottom of the Marianas Trench to the deepest parts of
the Earth's oceans, there were living things there.
The environmental sciences are a 20th century undertaking.
Geographical approaches are an important part of this undertaking, as can be seen in the
work of Russian botanist Nikolai Vabilov, who collected over 50,000 species of wild
plants from all over the planet.
He had a keen eye for noticing the geographic patterns of plants in their natural setting.
In 1920, he drew on his identification of these patterns to categorize eight zones with
different plants, which he termed biomes.
So biomes really represent one of the central organizing ideas in biogeography, in that
they bring together species adaptations.
They bring together large-scale patterns of climate and soils and geology and how those
are expressed in the types of organisms that you find in those areas.
Although Vabilov's eight groupings prove to be too crude for modern environmental studies,
he is considered to be the father of biomes, or as they are sometimes called, ecosystems.
The major biomes are as follows.
The tundra, a polar and high-altitude biome characterized by long cold winters, a short
growing season, and an absence of trees, coniferous forests, communities of evergreen pine trees,
forming a huge band across North America, Europe, and Asia, each with a short growing
season in highly acidic soils.
But deciduous forests are dominated by broadleaf deciduous trees, such as maples and oaks.
They have moderate precipitation with well-defined seasons of cold and warm.
Grasslands are treeless and dominated by grasses with a mixture of forms that over time have
produced highly fertile soils, forming the agricultural red baskets of the world.
Deserts, covering about a fifth of the world's land area, are places where evaporation exceeds
rainfall, soils are poor and nutrients, and the climate has warm or hot daytime temperatures
year-round.
Mediterranean scrub or chaperral, these low-lying plant communities, such as short bushy trees
and shrubs, are largely found along coastal regions and characterized by hot summers and
moderate winters.
Tropicals, the world's largest biome with the greatest biodiversity.
Today the tropics are divided into many subtropical environments that are warm all year-round,
often with an abundance of rainfall.
Rock, soil, water, air, life, the five major spheres of planet Earth.
But it would not be unreasonable in the 21st century to include an additional sphere—humanity.
Human activity has now become a unique and powerful force of interaction with the other
five spheres.
It has become the job of geography to connect them all.
Over the past few decades, the understanding of how the various spheres of the Earth—the
biosphere, hydrosphere, lithosphere, the atmosphere—connect with one another has increased dramatically.
One of the ways that we've increased this understanding is by observing the world as
people haven't been able to do before.
For example, we have satellites above the Earth now that are able to monitor the pulses
of life around the world across large areas, how it interacts with the distributions of
water and the changes in the atmosphere.
That satellite system, that network of satellites, allows us to find areas where there are problems
or where there are biological hotspots or where there's rapid change.
The study of biogography, in many ways, is a study of interconnections amongst all of
the different parts of the Earth's environmental cycles.
It brings together and requires us to consider climate patterns at a broad range of different
scales.
We also need to understand something about the geologic history.
That influences everything from the soils that are present.
Increasingly, one of the things that biogographers also have to understand is the fact that people
have had on the areas and the types of plants and animals that you have there.
Traditionally, that might have meant just understanding current influences.
So, some of the things that I study, for instance, are patterns of land use, forest fragmentation,
how those types of uses have impacted the organisms that you have in those areas.
There is, however, really a broader understanding that past land uses and past activities have
also shaped the things that we see today.
So, if you go, for instance, to forests in New England, it's one thing to study and understand
the types of plants that you find there based on current patterns, soils, climate, and human
activities.
But there's an imprint that really goes back from the centuries of land use that you've
seen in those areas.
If we imagine that our world is made up of different spheres, atmosphere, gases that
we basically exist in that support us, the hydrosphere, the water that we rely on, and
the lithosphere, the land under our feet, the soil that we use to grow our crops.
If we imagine that that's the way that the earth can be conceptualized.
Obviously, as science increased, as the amount of information we have, the technologies we
have increased, we began to sort of silo, we began to sort of specialize, so atmospheric
scientists worked on the atmosphere.
Hydrologists worked on the hydrosphere.
Soil scientists, pedologists, geomorphologists, geologists worked on the lithosphere.
And there was a time period, particularly I think during the 20th century, where we became
very, very fragmented.
And geography tried to keep it together in the face of demands for high degrees of technological
knowledge in order to tackle problems in those spheres.
What I've seen in the last 10 to 20 years is movement back towards a more comprehensive
earth systems approach that realizes you can't really study any of these satisfactorily
in isolation.
And we need tools then, and we need thinking that takes that very high level of information
about the atmosphere, coming from atmospheric scientists or from geographers who are climatologists
and working in meteorology, and can integrate that with the very, very precise and difficult
to obtain information that the hydrologists are producing, or the most recent biological
work from the geneticists that can bring that together again.
And with earth systems sciences, that approach is sort of really taken off.
And geography, because at the same time we've been developing spatial analytic tools, geographic
information systems, remote sensing, which is so important in a way of integrating that,
we've been able then to sort of come back into the fold in helping to pull that all
together.
Every place on earth's surface is a product of the physical and human elements found there.
But no place can be understood simply by cataloging the rocks, soils, waters, plants, and animals
that exist there.
Each of these components is part of a larger system that is most constantly changing and
interacting with all the planet's spheres, including the human sphere.
How every place on earth came to be the way it is is one of the most fundamental geographical
questions.
Answering that question requires considering how the characteristics of individual places
are shaped by larger processes we have just explored in this program.
We also saw how scale, both temporal and spatial, became a core geographical concept for understanding
these processes.
In the next program, I will show you how dividing earth's surface into regions can both help
us understand how geographical forces are shaping our world and be useful for grasping
where we are headed in the twenty-first century.
Thanks for watching Physical Geography, Making Sense of Planet Earth.
I'm Alec Murphy.
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