 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... All right, Mr. Ruchoff here. And in this lesson, we're going to learn how this picture is related to this one. And yes, that really is me. To give you a clue, it's all about how the continents in the mountains of the world have been created. So let's start by taking a look at the Earth. Now, some people have called our world the Big Blue Marble. And if you look at a picture of the Earth from space, it does kind of look like a blue marble. But I'm going to suggest the Earth is really like a baseball. Now, we'll talk about how the Earth is like the outside of a baseball in a few moments. But how the Earth is really like a baseball is we start looking inside. See, if we take a baseball we cut in half, we see it kind of looks like this. The center of the baseball is made up of cork with a little bit of rubber around it. The outside of the baseball is a thin layer of cowl hide. But most of the baseball we see is made up of tightly wrapped cotton or wool cords that are in between that cork's center and the cowl hide outer portion. Now, if we cut the Earth open, we see much the same thing. In the middle of the Earth is the core. And it's not made of a cork of rubber, of course, instead of made up of iron. Now, the core has two parts. It has the outer core and the inner core. They're both made up of iron, but the inner core is a solid iron and the outer core is molten iron due to the intense heat it's under. Now, the reason the inner core is still solid is because the enormous amount of pressure that it is under actually prevents it from being able to melt. Then we see there's an outer layer like the cowl hide of our baseball. The Earth's outer layer is called the crust and it's made up of solid rock. This is the part we sand on and we see pretty much every day. It is also the thinnest part of the entire Earth. In relationship to the rest of the Earth, the crust is about as thick as the skin of an apple is to the rest of the apple. Now, the thickness of the crust really depends whether it's part of the land or part of the ocean floor. See, the immense weight of the oceans presses down on the oceanic crust, making it only about four to five miles thick, but it's very, very dense. The continental crust, however, doesn't have the weight of the oceans pushing down on it, so it's much less dense, but it's much thicker anywhere between about 20 to 25 miles thick. But just like a baseball is mostly those tightly wrapped cotton wool cords in the middle, the Earth is made up of a layer called the mantle. Now, like the core, the mantle has two parts. The lower mantle and the upper mantle. Together, they make up 84% of the Earth's volume. And while the core is made up of iron, the mantle is made up of solid rock. So those are the basic components of the Earth, but let me now introduce you to a guy by the name of Alfred Wegener. And quite frankly, the reason why I even have this lesson is because of him. Wegener was a German meteorologist who studied the polar regions of Greenland. Now, despite not being a geologist, Wegener developed a theory that is essential to understanding the Earth's continents today. See, Wegener was a curious guy and thought it was interesting that the continents almost seemed like they fit together like a jigsaw puzzle. Now, he's not the first one to saw this, but Wegener was the first person actually found evidence to show that they actually did, at one point, fit together. See, he found that Africa and South America both had rock formations that did match up whenever you move the continents together. They learned of discoveries of fossils of the same prehistoric animals of plants that were found on several continents, even though they were a thousand miles apart. And once again, when you move the continents together, the fossil evidence came together. This led to a history that the continents move and at one point were all one large supercott known as Pangaea. What Wegener proposed is what we now know as the theory of continental drift. And what was the reaction of the rest of the scientific community? In short, they thought he was crazy. See, part of the problem was Wegener wasn't a geologist, so all the geologists thought that he was kind of muscling in on their action. And what made matters worse is the geologist demanded that Wegener explain what made these continents move and he couldn't do it. So what happened is the geologist used this against him to be able to discredit his theory. And unfortunately, Wegener died when he was 50 years old and he never got to see his theory accepted like it is today. But Wegener's theory gained traction when a geologist named Harry Hess joined the Navy during World War II. Hess commanded the supply ship USS Cape Johnson, which was equipped with a new piece of technology, Sonar. Sonar is kind of like a radar for water using sound waves instead of radio waves. The Navy used Sonar to alert ships of enemy submarines, but Hess realized his ship Sonar could also map the floor of the oceans. What he discovered was the earth really is like the outside of a baseball. See, when you look at the baseball, the distinctive feature is the stitches that hold the seams of the baseball's outer cover together. And what Hess discovered was that the earth also has seams that divide the oceans, and more importantly, they divide the crust of the earth into plates, tectonic plates. Now, research continues through the 1960s and discovered that the ocean floor nearest these seams were much younger than the ocean floor furthest away from these seams. This gave solid evidence supporting Hess's idea that the ocean floors were spreading, and this explained Wegener's idea of continental drift. For the spreading ocean floors pushes against the rest of the continents causing them to move. So what causes the ocean floors to spread? The answer is convection. And what is convection? Well, maybe the best example of convection is a lava lamp. A lava lamp is made up of a mixture of water, wax, and a light bulb at the bottom of the lamp. The light bulb will heat up the wax with both causes the melt and then to rise to the top of the lamp. At the top of the lamp, this wax is going to cool, and it's going to begin to drop back to the bottom where it's heated up again, and the cycle continues. This is convection, and we see it not only in lava lamps, but we see it in our atmosphere, in our oceans, and even in the mantle. The portion of the upper mantle below the tectonic plates is known as the asthenosphere, and while it is solid rock, it's solid kind of hollow, silly-putty solid due to the 4,000 degree temperatures that the upper mantle is under. So this very hot rock or magma will rise up, but it's stopped by the crust, which is hard rock. This leaves the magma nowhere else to go but to spread underneath the crust, but while it does so, it begins to drag the crust because of friction along with it, breaking and separating the crust. Where the crust breaks open, magma will fill in and be cooled by the ocean water and become new crust. This explains why the youngest crust is always by these ocean seams. This is the process that forces all the earth's plates to be in constant motion, and is with this continental drift caused by the spreading of ocean floors that creates landforms such as mountains. We call this theory that these moving plates create landforms, plate tectonics, after the word tecton, which means carpenter in greek. Now there are three major ways that the plates of the earth move. They can move away from each other, as we see in the middle of the oceans, we call this divergence. They can move towards each other and collide, we call this convergence, and they can move alongside each other, which we call transforming plates. Now we've already seen that diverging plates are created through magma convection. The longest of these divergent boundaries is actually underneath the Atlantic Ocean, and something which we call the middle Atlantic Ridge. Now not only does the mid-Atlantic Ridge run through the middle of the Atlantic Ocean, but it also runs through Iceland. So literally one part of Iceland is moving west, and one portion of Iceland is actually moving east. On land, a divergent boundary will create what is known as a rift valley, when the area between these two diverging plates drops. And the longest rift valley is the Great Rift Valley in Africa. In this picture, my wife and I are in Tanzania, and the Great Rift Valley is behind us. Now due to the plumes of magma that push up and create new crusts, volcanoes are common near rift valleys. This is why the Great Rift Valley is home to a great number of volcanoes. In fact over 60 volcanoes are in Ethiopia alone, and in Tanzania you have Mt. Kula Majaro, which is the tallest mountain in Africa. Now most landforms are created by convergent plates, and there are two major ways that these plates will come together and collide based upon what type of plates are involved. Remember how I told you that the crust under the seas is denser but thinner than the crust of the continents? This difference between oceanic continental plates changes what happens when plates collide. If you have two continental plates collide, they will fold up on each other, much like what happens if you take a towel on a table and you push the ends together. We call this convergent folding. And convergent folding has created some of the world's tallest mountains in the world, including the Himalayas in Asia that includes Mount Everest. The Himalayas were created when the Indian continental plate collided with the Asianic plate. But it's also important to understand that this process is continuing today. This means that Mount Everest is still growing just under a half inch every year due to this convergent folding. Now if you invite an Oceana plate to the party, you get what is called convergent subduction. Because Oceana plates are much denser, when they collide, it's going to force one of those plates down below the other and into the mantle. And it doesn't matter if you have two Oceana plates or an Oceana plate on the continental plate, if you have just one continental plate colliding, it's going to be convergent subduction. Now something happens when a plate is pushed back down into the mantle. Now due to friction, water and carbon being pulled in the mantle and it trains your pressure, some of this mantle is going to melt, rise to the surface, and create a volcano. This is why in areas where there are Oceana plates colliding with other plates, you're often going to find volcanoes. The Caribbean Islands, for example, is an example of such a subduction zone. But the largest subduction zone in the world is the Ring of Fire. No, no, no, not that Ring of Fire. This Ring of Fire. The Ring of Fire surrounds the entire Pacific Ocean and includes the western coast of North and South America and the eastern portions of Asia. And all there are over 400 active volcanoes in the Ring of Fire. In fact, 75% of all volcanoes are in the Ring of Fire, as is 90% of all the earthquakes. And what is an earthquake? Well, press your hands together as hard as you can. And while keeping the pressure, move one hand up and one hand down. At one point, what's going to happen is your hands are going to slip. And essentially, that is an earthquake. An earthquake is a sudden shift of the Earth's plates. The strength of earthquakes are measured by using something called the Richter scale. This is a logarithmic scale, which means that a 4 is actually going to be 10 times as powerful as a 3. Now a 4 on the Richter scale might knock a book off a bookshelf, a 6 will start to damage buildings, and 9 can completely level a city. The strongest earthquake in history happened in 1960 when a 9.6 earthquake hit Chile, which by the way, is in the Ring of Fire. Now because of the immense pressure on the crust, the Earth's crust is sometimes going to break, kind of like how concrete is going to break in the summer because of the expansion of the heat. These cracks in the crust are called faults, and this is where earthquakes occur most. Now probably the most famous fault line in the United States is the San Andreas Fault in California. It is a transformed plate where the Pacific plate is moving north, and the North American plate is moving south. Whenever these plates slip, California has an earthquake. The San Andreas Fault has become so famous it actually had its own movie. In fact, this is a poster from the movie and as I look at that poster I start wondering, do you think this actually could happen? The answer is no. See this actually shows a divergent boundary where the plates are moving away from each other and what we already said, the San Andreas Fault is a transformed boundary. So what this really means is, despite his name, you probably should not take your geology lessons from the rock. Now we know that earthquakes can be devastating on land, but if an earthquake occurs underneath the ocean, then it can create what is known as a tsunami. Now tsunamis unfortunately are common in subduction zones. They are caused by when a subducting plate begins to drag down the other plate. Now pressure is going to build up, and eventually this other plate is going to shift quickly upwards. When it does so, it's going to displace the water above the earthquake, creating a wave of energy that's going to travel as quick as a jet plane. This wave now in the middle of the ocean may only be a couple inches high, but as this wave comes closer to the shore, there is less water to displace the energy, which creates a higher and higher wave, which can be completely devastating. For example, in 2004, a 9.1 magnitude earthquake in Indonesia created a tsunami that killed nearly 230,000 people in Asia and even in Africa 5,000 miles away. Then there is something called hotspots. See, the Hawaiian islands are in the middle of the Pacific Ocean, thousands of miles away from a subduction zone. They are not caused by plate tectonics, they are actually caused by hotspots. Now there are about 40 hotspots around the world. These areas are where there is a plume of very hot mantle that will rise up and will actually burn a hole into the crust. Now as they do so, they're going to create a mound, and this mound eventually becomes an island such as the Hawaiian Islands. However, while the hotspot does not move, the crust above it does. So this hotspot is actually going to create many different islands or an archipelago, that is unless you're Iceland. Iceland has the distinction of not only being formed by a hotspot, it is also over the Mid-Atlantic Ridge. So while Iceland does expand east and west by about two centimeters every year, it remains over this hotspot. Hotspots are not only found in the ocean, but they're also found in land. Americans Yellowstone National Park is actually over a hotspot. This was the reason for the geysers such as Old Faithful and a great deal of volcanic activity. In fact, Yellowstone is actually what is called a supervolcano, an active supervolcano. It has had huge eruptions in history that has spewed volcanic ashes far as Texas. Fortunately, scientists don't think it's going to erupt for several more hundred years. So we talked about the composition of the Earth, Wigner's Continental Drift, and how plate tectonics creates landforms. So how does this picture relate with this picture? Well, in this picture, I'm standing in Thingvalir, Iceland, which is where the Atlantic Place is actually separating. In fact, everything to my right in this picture is moving to west, and everything to my left in this picture is moving east. And as we have explained, it is plate divergence seen in this picture that creates the mountains, what which we see in this one, which is Mount Everest. Spreading oceanic plates causes the continents to move, creating landforms through plate tectonics. All right, more to learn in future lessons, but until then, keep on learning.