 You are clear for launch. And with that, shut down your visors, O2 on, and prepare for ignition to O2. You can copy that, and, um... Let's reach off again. Alright, so in this lesson, we're going to start looking at the physical geography of the Earth. And when we begin to look at physical characteristics, we find there is a lot to it. There are oceans, there's mountains, there's rivers, there's weather and climate and vegetation, and so much more. To help explain these physical characteristics, we can use something known as the four Earth systems. The four Earth systems are atmosphere, lithosphere, hyersphere, and the biosphere. Now, just by looking at these terms, we can see they have all one thing in common. They are described as spheres. Now, normally we think about a sphere as being a shape like a ball. But the word sphere here means a section of the world that is unified by a particular characteristic. However, if you want to think about it, it's just basically a ball or a circle that we're putting all these characteristics into. That would work too. And we're also going to see that not only does each sphere have its own subcomponents, but all of these spheres interconnect with each other. So let's begin by looking at the atmosphere. The atmosphere describes the envelope of gases that surround the Earth. In the very word, atlas actually means vapor or a gas. So if you look at this footage from the International Space Station, you can actually see the atmosphere surrounding the Earth. And you can also see that the atmosphere has different layers. Now the highest layer is the exosphere, which is anywhere between 600 to 6000 miles above the Earth. Now as we go down from the exosphere, we go to the thermosphere, the mesosphere, and then we get down to the stratosphere that is anywhere between 9 and 30 miles above us. But the stratosphere is incredibly important because 90% of all the ozone gases in the atmosphere is found in the stratosphere. And why this is important because it is ozone, which actually absorbs and scatters ultraviolet radiation from the Sun. And without this ozone layer, there would be no life on Earth. Then there is the troposphere, which is what we live in, stretching from the ground to about 9 miles high. Now while this is the thinnest layer, it also contains 75% of all the atmosphere's mass. Now all together, all the gases in the atmosphere actually weighs an incredible 5 million billion tons, but it's distributed around the entire Earth. Now the average weight actually pressing down on you is 15 pounds for every square inch of your body. But you don't notice it because, well, it's normal for us. We've always had that around us. Now the atmosphere's importance is pretty easy to understand, as each breath you take, you're inhaling and exhaling this atmosphere. And without the atmosphere, we would not have the oxygen we need to live. But only 21% of the atmosphere is actually oxygen. 78% is nitrogen. This is why scuba divers may get something called decompression sickness or what is normally known as the bins. See, as a diver descends, the nitrogen they breathe dissolves into the muscle tissue as the water pressure increases. But unlike oxygen, the body doesn't use up this nitrogen. So when the diver comes back up to the surface, these nitrogen bubbles will expand kind of like a soda pop when you open it. This can cause pain, brain damage, and even death. While well-trained divers know how to avoid this from happening, it points to the fact that most of our atmosphere is actually made up of nitrogen. Now the remaining 1% of the atmosphere is made up of other gases, such as argon, helium, methane, and carbon dioxide. Carbon dioxide is the reason there is about 720 gigatons of carbon in our atmosphere, even though it represents only 400 of a percent of the atmosphere's gases. It is this carbon from the atmosphere that is the backbone of all life on Earth through something known as the carbon cycle. Now the carbon cycle is this transfer of carbon between the atmosphere, animals, trees, rocks, and the oceans. When we breathe, we exhale carbon dioxide about one kilogram a day. Trees and plants will pull in carbon dioxide from the atmosphere through photosynthesis, and then they will use this carbon to be able to create glucose in order to grow. The oceans also absorb carbon dioxide, where marine plants such as phytoplankton will turn this carbon into organic matter. Now people and animals may eat the plants, which reintroduces carbon into our bodies. Also, when trees and plants die, they will slowly begin to decay and decompose, returning carbon to the soil. Now this gives fertility to the soil, which allows it to be able to absorb moisture and provides the minerals that plants need to be able to grow. Now some of the carbon from the decaying plants and animals on the land on the oceans will become covered by more and more and more soil. Now speed forward several million years, and this process might find the carbon be hundreds if not thousands of feet below the surface. Now together with chemical reactions, pressure, and heat, this carbon now becomes fossil fuels such as oil and coal. Today's oil comes from 300 million years ago, and the result of the deposition of marine animals such as the phytoplankton that we talked about earlier. Now when we burn these fuels, we release this carbon into the atmosphere and the carbon continues. In fact, it is the burning of fossil fuels that most scientists believe is the reason why carbon dioxide levels in the atmosphere have increased since the industrial revolution and may be a contributing factor to the warming of the earth. Now the atmosphere describes the gases above the earth, but what about the ground itself? Litho in the term lithosphere comes to the word which means rock. So when we talk about the lithosphere in terms of the four earth systems, we're talking about all the rock in the world. This includes the earth's core, the mantle, and the rocky crust that we live on. It also includes the soil from which trees and plants grow. The crusts in upper mantle create continents and oceanic plates which move around and create the world's mountains and volcanoes through something known as plate tectonics in which we see both new crusts being created and old crusts being forced down below the earth's surface. The new crust is created by the spreading of the ocean floors and by volcanoes. In fact, an estimated one billion tons of new crusts are created each and every year, but about the same amount of crust is forced back down to the mantle by a process known as convergent subduction. This is a process that is shaped and reshaped the earth's surface for 3.2 million years. Then there are the oceans and all the earth's water in what is described as the hydrosphere with hydro meaning water. But the hydrosphere doesn't just describe the water we find in oceans and lakes, it also describes the water we find frozen in the glaciers and the water vapor we find in the atmosphere. In fact, this exchange of water between the hydrosphere and the atmosphere forms the water cycle. See, the water evaporates from the oceans and lakes and lives into the atmosphere as water vapor. This water vapor will condense and fall to the ground as rain or snow. Rainwater either flows off into rivers flowing back into the lakes and oceans or it percolates into the soil where it provides the moisture for plants to grow. They'll plants grow and give off water vapor through transpiration and along with the water vapor that is evaporated from oceans and lakes, the cycle continues. The water cycle. Now of the earth's over 300 million cubic miles of water, there is less than 3% that is actually fresh water. And of that fresh water, nearly 70% is trapped in the glaciers in the polar ice caps. So of all the water in the world, less than 1% is actually usable by us, which has made water an extremely important resource, which countries and nations have actually fought over before. Last is the biosphere, which comes from the Greek word bio, which means life. This includes all the life in the world to include the tiniest of microbes to the largest whales in the ocean. It also includes us. In the three previous systems, I described how each has a cycle. Well, within the biosphere, we have the actually, there's something called a life cycle, which biologists define as a serious changes in life of the organism. Think about the cycle of a caterpillar turning into a butterfly. This is an example of a life cycle. But just as we've seen in other earth systems, the biosphere is interconnected with the other three systems. Animals are part of the carbon cycle through the exhaling of carbon dioxide and plant photosynthesis. Plants give off a water vapor as part of a transpiration in the water cycle. And while the biosphere does not play a part in either the creation or enter the earth's crust, it does play a vital part in the creation of soil. Through the deposition of organic material, we get soil as fertility. But probably the most important thing to understand is the biosphere is dependent upon these three other systems for its survival. Without oxygen or ozone in our atmosphere, we would not be able to survive. We are dependent upon water to drink even for agriculture. The lithosphere not only gives us the soils we need to be able to grow our crops, but we mine its resources out of the ground to be able to build our societies. And as humans, we also have a profound impact upon each of these other systems. We can overuse and deplete these resources such as water. And through the pollution, we can have long lasting impacts to both the atmosphere and the hydrosphere. Together, the four systems are integrated and impact each other in major ways. And in this course, we'll talk about how the interaction of these earth systems have all had an impact upon the regions of the world. So until next time, keep on learning.