Welcome back to our Environmental Science series. On this talk, we will focus on our planet’s plate tectonics. This incorporates our plate boundaries, the structure of our Earth, and a little bit of history. Let’s get right to it!
First of all, our Earth is made up of three main components: crust, mantle, and the core. The Crust is made out of two parts, the oceanic crust which is responsible for the oceans on our planet, and the continental crust which is responsible for the land on our planet.
The crust is the surface of our planet. It is solid due to the cooling of the atmosphere, rain, and space. (We will dig in deeper on how the crust was formed in a future rock cycle talk) The crust is also the thinnest layer, only about 100 kilometers think. The oceanic crust is thin but dense thanks to the water pressure while the continental crust is thick but buoyant because of the many air pockets in between rocks and soil etc.
The Mantle is the layer in the middle, consisting of magma, and is semi-solid, therefore can move due to its partly liquid composition. The mantle also consists of two other parts: the lithosphere and asthenosphere. The Asthenosphere is the upper part of the mantle and is where convection currents occur. Convection currents occur when heat from the bottom of the mantle moves upwards, pushing cold downwards causing a cycle-like movement. These currents move the lithosphere. The Lithosphere consists of the uppermost mantle and the crust. The currents moving the lithosphere is what causes the plate tectonic movement. (More on this later)
The Outer core is primarily liquid iron because it has a lot of energy and heat that melts the iron. This layer is responsible for the magnetic field of Earth.
The Inner core is made of metals like nickel and iron, solid, and is the location of radioactive decay and nuclear fission, causing heat.
The concept of continental drift, the movement of continents, began in 1912 by Alfred Wegener who discovered it by observing similar fossils in different continents, landforms, glacial deposits (glaciers sliding on the top of the land due to a thin liquid layer, and therefore moving frozen components with it), and paleomagnetism (the orientation of metals in a rock based on their magnetic fields that exist in a pattern that show the production of new land). Although Wegener was right, no one believed him for he had no proof of how the plates moved, just proof that they did.
Harry Hess researched on seafloor spreading and observed cold seas and warm seas, discovering the thickness and speed of crusts that moved by mantle convection currents. He helped prove the theory of plate tectonics, how our crust is split into plates that move according to the movement of convection currents, and Wegener’s continental drift.
Plate tectonics is the reason why the supercontinent Pangaea broke up millions of years ago to reassemble to where the continents are at now.
Movements of these plates cause many different natural structures such as mountains, trenches, volcanoes, valleys, and ridges. So let’s talk about the different types of boundaries between these plates.
There are three different types of boundaries: Divergent, Convergent, and Transform.
Convergent boundaries are when two plates move towards each other (—–> <——). These can cause mountains if the two plates are continental. If the two plates are oceanic then the denser plate subducts, or sinks, under the less dense plate, forming a trench and a volcanic island on the less dense plate. If one plate is continental and the other is oceanic then the oceanic plate subducts forming a trench, and a volcanic range on the continental crust. Convergent boundaries destroy crust.
Divergent boundaries create more crust, and the two plates move away from each other (<—— ——>). When the two crusts are continental then a rift valley is formed, such as the African Great Rift Valley. If both the plates are oceanic then a mid-ocean ridge is formed, or an underwater mountain range because this opens up magma from the mantle to move upwards, which is cooled by the cold water, and therefore solidifies. An example of this is the Mid-Atlantic Ridge.
The third type of boundary is a transform boundary. This is when two plates grind up against each other and slip, causing a transform fault, a break in the crust, causing a huge release of stress and pressure. These boundaries are what causes earthquakes. They do not create, nor destroy crust. An example of this boundary is the San Andreas Fault.
That is it for this talk! In the next talk we will talk about the rock cycle, and in a future talk, we will go in-depth about natural disasters such as earthquakes, hurricanes, volcanoes, and storms. Remember to always look out for the environment! Comment if you have any questions and stay tuned for more talks on interesting topics. 😀
-Written By: Neil D. 2/16/2019
Living in the Environment –
G. TYLER MILLER, JR.
SCOTT E. SPOOLMAN