(ORDO NEWS) — What is plate tectonics? This is one of the many questions that you probably went through in geography lessons. In layman’s terms, plate tectonics is a scientific theory that describes the movements of the Earth‘s outer shell over its subsequent layer. Let’s take a closer look at what it is from a scientific point of view.
From the deepest ocean trench to the highest mountain, plate tectonics explains the features and movements of the earth’s surface in the present and past.
Plate tectonics is the theory (1912 version of Alfred Wegener’s Continental Movement Hypothesis) that the Earth’s outer shell is divided into large plates of solid rock called “plates” that slide over the Earth’s mantle, the rocky inner layer above the Earth’s core.
The solid outer layer of the Earth, which includes the crust and the uppermost mantle, is called the lithosphere. According to the Encyclopædia Britannica, it is 100 km thick.
Beneath the lithosphere is the asthenosphere, a viscous layer that is malleable due to the deep heat within the Earth. It lubricates the undersides of the Earth’s tectonic plates, allowing the lithosphere to move.
How does plate tectonics work?
The driving force behind plate tectonics is convection in the mantle. Hot material near the Earth’s core rises, while cooler mantle rock sinks. “It’s like a pot boiling on the stove,” Van der Elst said.
Meanwhile, geologists think of the plates above this seething mantle as bumper cars; they repeatedly collide, stick together, and then tear apart. Geologists refer to the places where segments meet and divide as plate boundaries.
They are believed to wrap around the Earth like the seams on a baseball. There are three ways to cross plate boundaries, and each one evokes a unique geological feature.
Convergent boundaries occur where plates collide with each other. Where these plates meet, the earth’s crust crumbles and folds into mountain ranges. For example, India and Asia joined together about 55 million years ago to create the Himalayan mountains.
Geologists have found that the Swiss Alps are rising faster than they are sinking due to erosion and are thus growing every year, according to a 2020 study in Earth-Science Reviews. However, when the mass of a mountain becomes too large to resist gravity, it stops growing.
According to the University of Hawaii at Manoa, erosion also inhibits growth by wearing down mountains, but because mountains can grow relatively quickly, erosion usually doesn’t win.
When two oceanic plates converge, a deep trench, such as the Mariana Trench in the North Pacific Ocean, is formed, which is considered the deepest point on Earth. Example of plate tectonics: photo of the Mid-Atlantic Ridge in the Thingvellir Valley in Iceland.
As the name suggests, diverging boundaries are tectonic boundaries where plates “pull apart” or move apart. This movement creates giant depressions on land, such as the East African Rift. In the ocean, this same process creates mid-ocean ridges.
Hot magma from the Earth’s mantle rises up these ridges, forming new oceanic crust and pushing the plates apart. Seamounts and volcanoes can rise along this seam, in some cases forming islands. The last type of plate boundary, the transformation boundary, exists where plates move sideways with respect to each other.
This sliding movement between plate boundaries causes an earthquake. According to National Geographic, tectonic plates move at a speed of 3 to 5 centimeters per year. That’s about as fast as human nails grow!
How many plates are there?
Since the Earth is spherical, its tectonic or lithospheric plates are broken into dozens of curved sections (like a cracked eggshell). According to the United States Geological Survey (USGS), each plate ranges in size from a few hundred to thousands of kilometers, and is classified as “large” and “small” depending on its size.
There are 7 main plates: North American, Pacific, Eurasian, African, Indo-Australian, South American and Antarctic tectonic plates.
However, according to a 2012 Nature article, earthquakes over the past few decades suggest that the Indo-Australian plate cracked 10 million years ago, creating a separate Indian and Australian plate that could increase the number of main plates to eight.
The Pacific Plate is still the largest of all tectonic plates. It is located under the ocean and has a size of 103,000,000 square kilometers.
The list of small plates of the Earth includes the Arabian, Caribbean, Cocos, Philippine, as well as the Scottish and Nazca plates. There are other plates located all over the world.
When did plate tectonics start?
Despite the fact that the age of the Earth is 4.54 billion years, the oceanic crust is constantly recycled in the zones of the tectonic process of the earth’s crust (subduction).
This means that the oldest seabed is about 200 million years old. The oldest oceanic rocks are found in the northwestern Pacific Ocean and the eastern Mediterranean. Fragments of the continental crust were discovered 3.8 billion years ago in Greenland.
With the help of clues left in rocks and fossils, geologists can reconstruct the past history of the Earth’s continents. Most scientists believe that modern plate tectonics took over from earlier planetary development about 3 billion years ago, based on ancient magmas and minerals preserved in rocks from that period.
According to a 2020 article in Discover magazine, researchers have found evidence that plate tectonics may have been active before 4 billion years ago.
Since the continents are located around the Earth, they sometimes come together to form giant supercontinents or a single landmass. One of the earliest large supercontinents, called Rodinia, formed about 1 billion years ago. Its disintegration is associated with a global glaciation called the Snow Land.
A later supercontinent called Pangea formed about 300 million years ago. Africa, South America, North America, and Europe pressed close together, leaving a distinctive pattern of fossils and rocks as soon as Pangea broke up, after which geologists were able to decipher these rocks.
The pieces left behind by Pangea, from fossils to corresponding coastlines along the Atlantic Ocean, have provided the first hints that the Earth’s continents are moving.
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