Rocks, Minerals, and the Earth's Structure
Rocks. They’re so common that we take them for granted, and they’re so annoying too. We kick them away when we trip over them, and then use them to hold picnic blankets in place. But what we don’t realize is that they are so important for us on Earth, and they’re responsible for the Earth’s structure! Yep, the planet that we live on is pretty much made up of....rocks!
Well, more specifically, it is made of minerals, which are solid inorganic substances that are naturally formed in nature. Rocks are simply mixtures of different minerals, volcanic glass, and organic matter, which are the remains of living and once-living things. But how were these rocks formed, to create the world that we live in today? The rock cycle can show us that, but before we get to the rock cycle, let’s discuss the three main types of rocks.
First, there are igneous rocks, rocks that are formed by cooling magma. One common example of igneous rocks is granite. Then, we have metamorphic rocks, rocks that get hot and then become so soft that they can even be deformed with intense pressure, and a common example of this is marble. Last but not least, we have sedimentary rocks. These rocks are formed when sediment is compacted and cemented together. Sedimentary rocks can include sandstone, or limestone. Most of the rocks on the Earth’s surface are sedimentary, while most of the rocks in the inner layers are either igneous or metamorphic.
Now, the rock cycle shows us how each of these three types of rocks can transform into one another.
Firstly, igneous rock turns into sediment, loose pieces of rocks, minerals, living things, through weathering and erosion. Then, under large amounts of pressure, sediment can compact and can cement into sedimentary rock. Meanwhile, heat and pressure from the Earth can squeeze and deform sedimentary rock into metamorphic rock. Then, metamorphic rock can be melted away by the hot temperatures deep inside the Earth to form none other than magma. And once magma rises close to the Earth’s surface, it is cooled and hardened...back into igneous rock!
The cool part about this cycle is that it can even occur backwards! We’ll start with igneous rock again. With heat and pressure from inside the Earth, it can be melted back into metamorphic rock. Then, the metamorphic rock can undergo erosion, which is breaking down, and compacting, which means to be compressed back together, into sedimentary rock. And then with melting and cooling, sedimentary rock will form igneous rock once more.
This shows that the cycle can continue again and again and again, as many times as necessary, and in any order. Another important note about this cycle is that matter changes and forms, but it is not created or destroyed. This is known as the law of conservation of matter, a very important concept in science that will be referenced multiple times.
So yeah, next time you kick that useless rock for tripping you, consider that it was once maybe an igneous rock or a metamorphic rock below the surface of the Earth, which would tell us a lot about the pressure and temperature inside the Earth. Rocks do have more of a story to tell than we’d think, and maybe they’re not entirely useless after all.
Layers of the Earth
On the surface of the Earth, we see grass, trees, perhaps mountains and buildings, and the whole wide world that we know. But the history of this planet and even some of our stories all lie in the layers below the surface. So, let’s look at all of the layers of the Earth, to figure out this history.
First, we’ll go into sedimentary rock, which we touched on in the previous lesson.
Sedimentary rock is formed layer-by-layer, with the oldest layer on the bottom, and the other layers piling on top of it in chronological order. These layers are called strata.
According to the principle of superposition, as these layers accumulate and strata get formed overtime, rock at the bottom will ALWAYS be older than rock towards the top. Scientists use the locations of layers relative to one another to date rocks, strata, and fossils, called relative dating. That’s why when archaeologists find artifacts, they are able to date which time period the artifacts came from!
Now, all of these sedimentary layers are a part of the Earth’s surface and the topmost part of the crust. Most rocks on the Earth’s surface are made of silicon, oxygen, and small amounts of aluminum, iron, and other elements. However, as you dig further down, the layers become very different. You can think of it like a peach!
First, we have the Earth’s crust, which is the outermost layer of the Earth, like a peach’s skin. The crust is mostly soil and rock. It’s the thickest between landmasses and the thinnest under the ocean. The crust can be 70 kilometers deep at some points!
Then, we have the mantle, Earth’s largest layer, just below the crust...just like the flesh of a peach. It is made of hot gooey magma that slowly circulates in gigantic convection currents. These convection currents are forces that drag the crust around.
After this, we have the outer core, which is just below the mantle, and is similar to the flesh of a peach right outside its pit. The outer core is mostly molten iron and nickel, and the liquid outer core gives Earth its magnetic field.
And then...the inner core. The innermost and hottest portion of the Earth. The pit of the peach. This portion is mostly solid iron and nickel, and is hotter than the outer core. And...by “hotter than the outer core”, I mean 9,392 degrees fahrenheit! However, the inner core of the Earth still manages to stay solid. This is because of the intense pressure from all directions that it faces, forcing atoms to stay as closely packed together as possible.
Yeah, the Earth is far more complicated than just the surface. There are so many layers to it, just like a peach! We now know about the stories that each and every layer tells, but what is the importance of having all of these layers? Why are they there? We’ll find out in the next lesson.
Oobleck Layers Of The Earth
Cornstarch (at least 1.5 tbsp per person)
Water (at least 1 tbsp per person)
Plastic cups (at least 1 cup per person)
Plastic spoons (at least 1 per person, for stirring)
Procedure (for each student):
Add cornstarch and water into a plastic cup. Mix cornstarch and water until the mixture is consistent. You have successfully created oobleck!
Swirl the plastic cup around and let the oobleck move around. Does the oobleck appear solid or liquid?
Take a piece of the oobleck and roll it between your fingers. Does the oobleck appear solid or liquid?
Leave this piece of oobleck on the palm of your hand, and tilt your palm downward, letting the oobleck roll to your fingers. Does the oobleck appear solid or liquid?
Put all the oobleck back into the cup. Poke it and punch it. Does the oobleck appear solid or liquid?
Experiment with the oobleck for a few more minutes, and come to a conclusion about what state of matter it fits into (solid, liquid, or gas). What can this experiment tell us about the state of matter of the asthenosphere inside the Earth?
Tectonic Plate Motion: Part 1
As we all know, the Earth is split up into various oceans and seven continents. Each continent has so much diverse terrain, such as mountains, valleys, canyons, and cliffs. So, let’s look into how all of these interesting places were created.
All the action happens in the lithosphere, which is the Earth’s crust and the layer of the mantle directly connected to the crust. The Lithosphere is broken up like an eggshell into large parts called tectonic plates. These plates move around, on top of the inner layers of the mantle, with the help of convection currents and gravity.
In fact, mountains, earthquakes, and volcanoes are all caused by lithospheric plate activity, or tectonic plates that haven’t had a smooth relationship. Let’s talk a little bit about these phenomena.
First, we’ve got fault-block mountains. When plates move away from each other, they create faults, or rock layers that are pulled apart. These pulled apart rock layers cause large blocks of rock to tilt and separate completely, forming mountains with sharp, jagged, parallel ridges above wide, flat valleys. Some examples of this are the Teton Range and the Sierra Nevada, two beautiful mountain ranges.
Next, there are folded mountains. When plates move towards each other, collide, and squish together, they form folded mountains. The Appalachian Mountains and the Himalayas are two prominent examples of folded mountains. You’ll notice that these mountains have peaks that are less jagged, and a little more rounded, and this is how you can differentiate them from fault-block mountains.
Last but not least, we have volcanic mountains. When the lava from a volcano cools, it creates a layer of hardened lava on top of the volcano. These layers keep piling up and piling up, until the volcano forms a cone-shaped mountain. Some examples of volcanic mountains include Mt. Kilimanjaro, Vesuvius, and Mount Fuji, some of which are notoriously dangerous.
So the next time you visit a national park, you’ll be able to identify all that messy, destructive action that happened, to create the beautiful place that it is today. In the next video, we’ll discuss some more of the consequences of tectonic plates moving in different ways. See you then!
Tectonic Plate Motion: Part 2
The last lesson covered the mountains and the various types of terrain that can be formed by tectonic plates...but now, we’ll take a closer look at what exactly happened at their boundaries, to form mountains, volcanoes, valleys and more! So, what could happen with tectonic plates that...don’t really have a smooth relationship? There are three possibilities: divergent boundaries, convergent boundaries, or faults.
Firstly, there could be a divergent boundary, or plates moving apart, and this could have different outcomes with oceanic plates (plates that contain oceans at their surface), and continental plates, which contain land at their surface.
With oceanic plates, magma from the mantle will get pushed up as plates move apart. When it comes in contact with the outside air, it will harden, forming a new crust to fill the gaps between these two plates. However, the new magma is less dense than the surrounding area, which means that it will lift up and form ridges of igneous rock in the seafloor.
Meanwhile, with continental plates, as these plates move apart, they will form rift valleys, or areas of the Earth where the land looks torn apart. An example of a rift valley would be the East African rift. Looks pretty cool, doesn’t it?
Next, we have plates colliding, or convergent boundaries. In the case of two continental plates colliding, massive earthquakes can occur along these boundaries, and these earthquakes often go extremely deep into the crust. However, when an oceanic and continental plate collide, the oceanic plate sinks into the mantle, and the rock around this area melts to form magma. Then, magma rises, and layers of magma pile on top of each other, as described in the previous video, to create none other than a volcano.
The third type of boundary is a fault, which occurs when plates slide past each other. This creates enormous fractures in the rock bed, like large cracks, and also causes earthquakes. During earthquakes, rocks get strained from rubbing against other tectonic plates. They build up potential energy from getting stuck on each other, and then release all this potential energy. This causes vibrations that move outward like a ripple effect, which then creates an earthquake.
Now that we know about all of these boundaries that have shaped our Earth’s terrain, it is also important to note that these plates are not only responsible for all the mountains, earthquakes, and volcanoes. In fact, since these tectonic plates have been moving ever since the creation of the earth, they’re even responsible for things as big as our oceans and continents!
Our continents were originally connected, forming a huge landmass called pangaea. However, overtime, they separated. This is why the continents look like they would fit together well, like how South America fits underneath Africa, and the side of Australia fits around Antarctica. Also, once you fit all the continents together, you will notice that the fossil remains across different continents are around the same location. For example, the fossil remains of the Cynogathus, a triassic reptile, are found in regions of South America and Africa that are right next to each other. Fossil remains of the triassic reptile Lystrosaurus are similarly found in areas of Africa, India, and Antarctica, which are right next to each other as well. Pretty cool, isn’t it?
Yeah, tectonic plates are not just responsible for the mountains and interesting landforms we see on Earth, but they’re even responsible for the formation of our continents all those millions of years ago. That makes things a lot more interesting! In the next unit, we will be talking more about what lies above the surface of the Earth, the atmosphere, as well as how it affects the water cycle, weather, and climate. See you then!