Have you seen Ice age movie franchisee? The whole saga of Ice age movies is fun and entertaining. But, there is one that coincides with our recent topic plate tectonics and continental drift. Yes, I am talking about the ice age- Continental drift where Manny had to fight with a Gigantopithecus to save his family and friends on ever-changing continents.
Namaste folks, we are in the third chapter of the History of earth series, and after the let us drift and move through the violent mechanism of plate tectonics and continental drift. I think about writing on another important event but instead, I picked plate tectonics as the write-up. The importance of plate tectonics can be understood from one single line only that whatever geological feature we have including their location has all resulted from plate tectonics. If we interchange two plates the world and its dwellers would be vastly different. Miniscule movement of plates can mean catastrophe for us.
In the whole of geophysics, there is probably hardly another law of such clarity and reliability as this-that there are two preferential levels for the world’s surface which occur in alternation side by side and are represented by the continents and the ocean floors, respectively. It is therefore very surprising that scarcely anyone has tried to explain this law.
Alfred L. Wegener
The history of plate tectonics
It took years for mainstream science to understand plate tectonics and give credit to Alfred Wegener. If you think for a minute it does feel unreal that Alfred Wegner was so smart that he came to this brilliant solution that continents can actually move.
Alfred Wegener as a meteorologist was working on paleoclimate and he discovered the range of different climate patterns which seemed bizarre to him. On top of that when you look at continents especially Africa and South America it looks like they were the same landmass broken apart due to some reason. The eastern boundary of South America and the western boundary of Africa fits perfectly together. it is true to some extent for North America and Europe also. Many fossils of the same species like dinosaurs and fern trees have been found in Africa and South America. The same kind of mountain chain has been found in Africa and South America alike. It shows that mountains started building on united Pangea but after continents broke apart they grew on the separated landmass.
All this as well as other proves had made Wegener proposed his famous hypothesis that met with heavy criticism. Decades after Harry Hess had proposed and given evidence for seafloor spreading that become the first solid prove for plate tectonics. After that subduction was discovered too and continental drift got the recognition it deserved. There are 9 major plates and by their name, you can deduce what continents are on top of them. North American plate, Eurasian, South American, African, Indian, Australian, indo-Australian, Antarctic, and pacific.
The mechanism of plate tectonics
The movements of tectonic plates are driven by the mantle. Although mantle mostly consists of solid magma however it is mobile enough to move tectonic plates above it slowly in different directions. Scientists have named it mantle convection where hot magma near the outer core gets heated enough to travels up and when it reaches near the surface it cools enough to sinks back in. This movement of magma creates enough momentum for plates to travel basically slide above the mantle.
How two tectonic plate interacts?
To understand the mechanism of plate tectonics we have to understand seafloor spreading and subduction. To understand the above two terms better we need to know the way plates behave. When tectonic plates interact with each other they create 3 types of plate boundaries, convergent, divergent and transform. A convergent boundary is where two plates collide with each other. In this scenario, two things can happen. Firstly, either one plate (heavier basalt oceanic) moves underneath the other (granite lighter continental) plate which creates subduction zones like Ring of fire (pacific ocean). Secondly, both plates can collide and move upwards creating mountains like the Himalayas.
A divergent boundary is where two plates move away from each other. Mid oceanic ridge is a divergent boundary where planet earth continuously creates new crust. We have to remember that the earth is not increasing it is the same as its origin 4.5 billion years ago so, some parts of the plates must be going somewhere. This is where subduction comes into play. The convergent boundary where one oceanic plate and one continental plate collides the heavier oceanic plate subduct/goes underneath the lighter continental plate. The oceanic plate sinks deeper in the mantle and unites with the earth’s interior.
Now comes the third type of behavior transform plates, where two plates collide against each other both of them refusing to leave their place. San Andreas fault is situated just offshore of san Francisco a metropolitan area. Here pacific plate is having hand-to-hand combat with the North American plate.
How tectonic plates move?
After knowing about the plate’s behavior we can jump into seafloor spreading and subduction. Some of you must have heard of the mid-oceanic ridge as it is the largest mountain range on earth. Around WW2 a USA naval veteran Harry Hess had done a very detailed survey of the ocean floor and proposed the seafloor spreading. Like continental drift, his ideas also met skeptics but the extensive tangible prove had made many agreeing with his theory.
Mid oceanic ridge is run across the oceans creating a chain of mountains. Here earth crust is very weak. Ridge opens up due to pressure giving way to magma. This magma flows just like volcanic lava coming out in eruption. Lava spread on both sides and through time it solidifies into the solid dense basaltic plate. This way the ocean plates keep on getting larger. This is called seafloor spreading.
The mid-oceanic ridge is accompanied by volcanic eruptions and hydrothermal vents. I have mentioned in my first blog post that hydrothermal vents are our best bet for the origin of life, especially black smokers. Black smokers are one kind of vents where cold water of ocean floor when comes in the contact with lava it produces black smoke rich with iron and other metals. Scientists have found hydrothermal vents choked full of micro and macro life forms. As the mid-ocean ridge is thousands of meters below the sea level volcanic eruption happening here are normally not lethal for life on earth.
Subduction zones are where the oceanic plate subducts underneath the continental plate. They are recycling machines of the earth as seafloor spreading produces more crust subduction zones digest some portion keeping the balance intact. Ocean plates are made up of basalt so it is heavier and sinks under granite continental plates. Subduction zones are accompanied by trenches. Some of the deepest trenches in the world are also found under the ocean. Mariana trench with its deepest point, challenger deep run across the Mariana Islands. Here pacific plate subducts under the granite philippine plate. The ring of fire comprises infamous subduction zones that run across the whole boundary of the Pacific Ocean. Throughout the earth’s history, these subduction zones are hotspots of earthquakes and volcanic eruptions.
The glimpse into the future
The seafloor spreading and subduction drive the motion of tectonic plates. Tectonic plates grow 2–3 inches per year same as your fingernails. In one year you might not see enough changes however fast forward millions of years and a different planet. You will see those plates gliding on the globe dancing here and there and colliding and smashing. All the supercontinent in past Pangaea, Nuna, Rodina, Gondwana have from plate tectonics. Scientists have calculated the current movement of tectonic plates and they estimated that after 250 years all of the landmasses will be together in supercontinent Pangea ultima.
African plate will collide with south Europe turning the Mediterranean sea into Mediterranean mountains. Along with that Africa will split open from the Great Rift Valley separating Somalia, parts of Ethiopia, Tanzania, and Kenya from the main landmass. North America is moving away from Europe. Subsequently, the Pacific Ocean will shrink and the Atlantic ocean will get bigger.
The composition of the earth and its relation with plate tectonics
Earth is the only planet in the solar system that has a well-developed plate tectonic mechanism unlike any planet in the solar system. Its inner structure has a very important role in plate tectonics and continental drift that we can understand by two methods. The composition of the earth as per the chemistry of layers has basically three layers, core, mantle, and surface. The mechanical differentiation depends more on the works of layers and this separates the earth into 5 mechanical layers. The lithosphere is the outermost layer of earth which includes every geological structure. It is 10–200 km wide. Then comes the asthenosphere which is the same as the lithosphere in composition but due to the pressure and heat from inside it is kind of semi-solid. We cannot say it is liquid but mobile enough that gives momentum to tectonic plates.
After this comes the mesosphere with molten lava in very high pressure and heat conditions. After this layer, we reach the outer core which is composed of iron-nickel and other metal in molten conditions. It is a thick semi-solid material that generates a strong magnetic field around the earth. This field protects the earth its habitant from the harmful rays of the sun. Without it, not even water could have sustained on earth. The innermost layer is the inner core which is a solid ball of iron and nickel. The radioactive decay of the inner core produces enough radiation that keeps the outer layers molten.
- A well-detailed post on plate tectonics for Beginners by Live Science.
- A short and easy video on plate tectonics by Cary Graham.
- Two documentaries Naked science- Colliding continents and National Geographic- Lava driven world. Consider watching them if you want to know more in-depth about the topic in addition to its relation with other natural phenomena.
- A very detailed post by Britinaca on plate tectonics. Therefore, those of you who want details do refer to it.
- Another post on plate tectonics by National geographic.
It must have appeared almost as improbable to the earlier geologists, that the laws of earthquakes should one day throw light on the origin of mountains, as it must to the first astronomers, that the fall of an apple should assist in explaining the motions of the moon.
The theory of plate tectonics and continental drift is widely considered one of the greatest physical theories of the 20th century as well as one of the greatest theories for humanity. There is so much more to learn and discover about it. Scientists are still searching how plates interact with the earth’s interior on a deeper level and how this interaction fuels natural disasters. I will dig a little deeper into plate tectonics in the next chapter. Until then stay tuned and do the Revelation.
Originally published at https://www.thescientificrevelation.com on January 18, 2021.