Earth’s crust is divided by several tectonic plates in various sizes. Plate tectonics is a theory that studies the structure of those plates and explains how they are constantly gliding over the mantle. In other words, the plate tectonics theory explains how the rigid and hard slabs of rock (plates) move on the underlying mantle and enable scientists to measure the movement of landmasses.
We already know that our planet rotates around its axis. But, did you know that the surface of the planet where we currently stand also moves, although we do not feel it? Yes, earth’s crust moves, however, compared to the earth’s rotation, the surface of the planet moves at a much slower pace (only a couple inches per year).
History of Plate Tectonics
It all started with the curiosity of German polar explorer and geophysicist, Alfred Wegner. He was curious to figure out why the fossils of the same plants and animals, and exact similar rock formations exist in different continents, although they are separated by the world oceans. He reasoned that millions of years ago, the continents were part of a single landmass, a supercontinent called Pangea.
Wegner believed that the same animal and plant species spread all over the supercontinent before its parts broke apart and floated away, creating 7 continents we have today.
He called his theory Continental Drift and introduced the idea in his book called “Origins of Continents and Oceans” in 1915. He was also inspired by how the shorelines of African and South American continents interlocking when brought together.
Even the edges of some other continents somehow come together when placed next to each other. You can also confirm this evidence independently by looking at the shorelines of the continents on a world map.
Unfortunately, Wegner could not come up with a convincing model that could explain how continents broke apart and moved away. Therefore, his idea was discarded by scientists of his time.
Also, the idea of Continental Drift was a new theory for the scientists who originally thought that earth developed rigid landmasses, mountains, and oceans due to the phases of global warming and cooling. Concisely, they believed that earth was currently cooling and shrinking.
Although the theory of Continental Drift was not successful, his ideas sparked a new debate among scientists. They tried to find an answer to the same question Wegner had: How come the continents hold so many similarities, although they are separated by oceans?
Plate Tectonics theory took off after World War II.
During the war, more advanced radar technologies were invented and used to detect the German submarines. However, that effort eventually led to an even bigger discovery. Using technology, scientists could map the seafloor and detect the evidence of seafloor spreading.
The seafloor spreading is a process, during which molten material rises from the mantle, and comes out between two plates. As a result, two plates split apart and move away from each other, causing the seafloor to expand (spread).
After World War II, serious funding was allocated for ocean research. In the 1950s, American and British researchers discovered that “the earth’s magnetic field wasn’t stationary” as believed previously. Eventually, during the 1960s, researchers found out that it was the continents that moved, impacting the locations of magnetic fields.
More advanced modern technologies accelerated the study of plate tectonics. Nowadays, we can measure the movements of plates and determine the areas that are prone to earthquakes and volcanoes with greater precision. All that is, of course, become possible thanks to modern science and technology.
What are the names of tectonic plates?
According to the World Atlas, there are 9 major tectonic plates and several minor plates and microplates on this planet. Major plates include North American plate, Eurasian plate, African plate, Indian plate, Australian plate, Indo-Australian plate, South American plate, Pacific plate, and Antarctic plate.
The largest tectonic plate is the Pacific plate, which is measured to be around 39,884,350 sq. miles (103,300,000 sq. km) in size. The second-largest tectonic plate is the North American plate (75,900,000 sq. km) followed by the Eurasian plate (67,800,000 sq. km).
Usually, world maps illustrate the major plates, while smaller plates are being left out from the majority of maps. Scientists categorize the plates as major, minor, and microplate, based on the size of their territory. For instance, an area of a major plate is greater than 7,7 million square miles (20 million sq. km).
Small plates have a size of less than 7.7 million square miles (20 million sq. km) and greater than 386,100 square miles (1 million sq. km.). Regardless of their size, both large and small plates are hard and rigid in nature and they glide over the mantle which is the much denser than they are.
Arabian plate, Amurian plate, Caribbean plate, Caroline plate, Nazca plate, Philippine sea plate, Burma plate, and Scotia plate are some of the many minor plates of this planet.
The sizes of the microplates are less than 386,000 sq. miles (1 million sq.km). Examples of microplates are the Lwandle plate, Tonga plate, Woodlark plate, Rivera plate, Iranian plate, Solomon Sea plate, Mariana plate, and North Andes plate.
How do tectonic plates move?
Earth has three main layers: the core, the mantle, and the crust. I explained each of these layers in my previous post. Those layers have different characteristics. For example, the core of the earth is as hot as the surface of the sun, and that heat gets to the upper layers of the earth creating the burst of energy. The convection current theory explains this theory more thoroughly.
What is convection currents theory?
Convection currents theory explains how liquid, gas and molten materials rise, spread, and sink due to the energy coming from heat. Concisely, when the core heats the materials in the earth’s mantle, those materials rise as liquid or gas. Once those materials rise and come to the surface, they cool down and sink again. This process is circulating continually thousands of meters below our feet, causing the tectonic plates to move.
Real-life examples will be magma flows caused by convection currents. You can also observe the convection currents in boiling water. When the bottom part of the water heats, the molecules at the bottom rise up, generating a movement.
What are the types of plate tectonic boundaries?
Due to the movement of tectonic plates, three types of boundaries appear between the plates. Those are:
Divergent boundary – develops when two tectonic plates move away from each other.
Convergent boundary – develops when two tectonic plates collide with each other, causing one or both of the tectonic plates to rise up into the mountain ranges.
In some cases, one of the plates gets bend and pushed downwards into the mantle. Now, you know how mountains grow up to be that tall.
Transform boundary-develops when tectonic plates slide past each other. In other words, the plates move to opposite direction and grind each other.
Earthquakes and volcanoes are more common at tectonic boundaries due to the movements of plates.
Did you know? The largest tectonic plate on this planet, the Pacific plate, locates under the Pacific Ocean and it moves only 2.75 inches (7 cm) per year. And, it moves towards the northwest.