# Plate Tectonic Theory with 20 MCQs

Plate Tectonic Theory

Plate Tectonic theory states that the Earth’s hard outer crust, the lithosphere, is divided into plates that move over the asthenosphere, the molten top portion of the mantle. Oceanic and continental plates come together, spread apart, as well as interact at borders all over the world.

Table of Contents
##### Introduction to Theory

After Alfred Wegener’s theory of continental drift, great advances were made in geophysical techniques that allowed the mapping of ocean floors, measurement of Earth’s magnetic field, gathering and recording seismic data, etc.

In 1966, these developments in geophysical techniques led to the introduction of concept of Plate Tectonics. This concept was formulated by Canadian Geophysicists named J. Tuzo Wilson in 1966. It can be said that this theory is the scientific mechanism of continental drift theory proposed by Wegener.

##### Principles of Theory
###### Plates

From the inmost sea trench to the huge mountain, plate tectonics describes the attributes and movement of the Planet’s surface area in the present and the past. Plate tectonics is the theory that Earth’s external shell is split right into huge slabs of solid rock, called “plates,” that slide over Earth’s mantle, the rocky inner layer above Earth’s core.

Earth’s solid external layer, which includes the crust and also the uppermost mantle, is called the lithosphere. It is 100 km (60 miles) thick. There lies the heavier and hot material known as the Asthenosphere below the lithosphere.

The rigid, lighter, and outer lithosphere is supported below by the more plastic and heavier material of the asthenosphere. The thickness of plates in oceans varies from 50 – 100 km. By contrast, continental blocks are 100 km thick and, in some regions, may exceed 150 km.

###### Movement of Plates

Another basic principle is that each plate moves as a single independent unit. The mobile and plastic nature of the mantle is believed to facilitate this motion while the push is provided by the accretion of material to plate at the mid-oceanic ridges.

Meanwhile, geologists imagine the plates over this roiling mantle as bumper vehicles; they consistently collide, stick, after that tear apart. Geologists describe the places where segments met and also divide as plate boundaries. They’re believed to wrap around the Earth like seams on a baseball.

Since all plates move distinctly as a unit, all the interactions occur at plate boundaries. The large-scale structural features of the Earth such as continents, basins, islands arcs, trenches, mountain belts, etc. all are thought to be produced as a result of interactions between plates along dynamic margins.

##### Plate boundaries

Plate boundaries are the edges where two plates meet. Most geologic activities, including volcanoes, earthquakes, and hill building, occur at plate boundaries.

Further Reading:  Alternating Current (AC) Generator

##### Convergent Boundaries

The movement of two plates in opposite directions collide along the margins i.e., one plate subducts under the other and the lower plate may be absorbed in the mantle. The boundary where plates are being destroyed is called the convergent boundary.

Three convergent boundaries are present, all of them somehow including a subduction area. In the continent-continent collision, the subduction zone has currently vanished however can be seen below the surface area.

Subduction areas create lots of igneous lava that rises to the surface area to form volcanic mountains (volcanic arcs; island arcs). At convergent boundaries, the oceanic lithosphere is constantly damaged by coming down into a subduction area. This is because the nautical rock is heavy, contrasted to the continents, and also sinks conveniently.

##### Divergent Boundaries

Plates relocate apart at mid-ocean ridges where new ocean floor forms. Between the two plates is a rift valley. Lava streams at the surface area great rapidly to become lava, yet deeper in the crust, the lava cools down extra gradually to form gabbro.

So, the entire ridge system is made up of igneous rock that is either extrusive or invasive. Earthquakes are common at mid-ocean ridges because the motion of magma, as well as nautical crust, leads to crustal trembling. The substantial majority of mid-ocean ridges are located deep beneath the sea.

##### Transform Boundaries

A transform plate boundary occurs when two plates slide past each other, flat. Very deep faults typically establish within the plates, most prominently striking throughout the ridge axis. A widely known transform plate boundary is the San Andreas fault, which is responsible for California state’s earthquakes.

### MCQs:

• What is the Plate Tectonic Theory primarily concerned with?
• A) The study of ocean currents
• B) The movement of Earth’s tectonic plates
• C) The formation of sedimentary rocks
• D) The study of atmospheric pressure
• Answer: B) The movement of Earth’s tectonic plates
• Who formulated the concept of Plate Tectonics?
• A) Alfred Wegener
• B) J. Tuzo Wilson
• C) Charles Darwin
• D) Marie Curie
• Answer: B) J. Tuzo Wilson
• What is the lithosphere made up of?
• A) Solid outer shell of Earth
• B) Molten lava
• C) Gaseous compounds
• D) Liquid metal
• Answer: A) Solid outer shell of Earth
• What lies below the lithosphere?
• A) Mesosphere
• B) Asthenosphere
• C) Crust
• D) Outer core
• Answer: B) Asthenosphere
• What is the approximate thickness of the lithosphere?
• A) 10 km
• B) 50 km
• C) 100 km
• D) 200 km
• Answer: C) 100 km
• How do plates move according to the Plate Tectonic Theory?
• A) Individually and independently
• B) Attached to each other
• C) They do not move
• D) In opposite directions only
• Answer: A) Individually and independently
• What geological activities occur mostly at plate boundaries?
• A) Rainfall
• B) Volcanoes, earthquakes, and hill building
• C) Desert formation
• D) Glacier movements
• Answer: B) Volcanoes, earthquakes, and hill building
• What type of boundary involves the collision of two plates?
• A) Convergent boundary
• B) Divergent boundary
• C) Transform boundary
• D) Conservative boundary
• Answer: A) Convergent boundary
• What occurs at mid-ocean ridges?
• A) Formation of mountains
• B) Formation of valleys
• C) Formation of new ocean floor
• D) Formation of deserts
• Answer: C) Formation of new ocean floor
• What is responsible for the earthquakes along transform boundaries?
• A) Subduction
• B) Collisions
• C) Sliding past each other
• D) Divergence
• Answer: C) Sliding past each other
• What is the process at convergent boundaries where one plate moves beneath the other?
• A) Subduction
• B) Divergence
• C) Collision
• D) Transforming
• Answer: A) Subduction
• Which type of plate boundary involves plates moving apart?
• A) Convergent boundary
• B) Divergent boundary
• C) Transform boundary
• D) Conservative boundary
• Answer: B) Divergent boundary
• What geological feature is formed at divergent boundaries on the ocean floor?
• A) Mountain ranges
• B) Rift valleys
• C) Volcanoes
• D) Islands
• Answer: B) Rift valleys
• Which boundary involves plates sliding past each other horizontally?
• A) Convergent boundary
• B) Divergent boundary
• C) Transform boundary
• D) Conservative boundary
• Answer: C) Transform boundary
• What is a well-known example of a transform plate boundary?
• A) Himalayan Mountains
• B) San Andreas Fault
• C) Mid-Atlantic Ridge
• D) Andes Mountains
• Answer: B) San Andreas Fault
• How are mountain ranges formed at convergent boundaries?
• A) By volcanic eruptions
• B) By subduction of one plate beneath another
• C) By plates moving apart
• D) By sliding past each other
• Answer: B) By subduction of one plate beneath another
• What type of plate boundary is associated with the formation of island arcs?
• A) Convergent boundary
• B) Divergent boundary
• C) Transform boundary
• D) Conservative boundary
• Answer: A) Convergent boundary
• At what type of boundary do earthquakes occur due to the grinding of two plates against each other?
• A) Convergent boundary
• B) Divergent boundary
• C) Transform boundary
• D) Conservative boundary
• Answer: C) Transform boundary
• What is the term for the area where two plates are being destroyed at a convergent boundary?
• A) Subduction zone
• B) Rift valley
• C) Mid-ocean ridge
• D) Island arc
• Answer: A) Subduction zone
• Which boundary type is responsible for the formation of new ocean floor?
• A) Convergent boundary
• B) Divergent boundary
• C) Transform boundary
• D) Conservative boundary
• Answer: B) Divergent boundary
Further Reading:  Wave Motion and Relation of Wavelength with Velocity and Frequency

### Plate Tectonic Theory Summary:

The Plate Tectonic Theory revolutionized our understanding of Earth’s geological processes. It asserts that the lithosphere, Earth’s outer crust, is fragmented into tectonic plates that float and move atop the asthenosphere. Here’s a breakdown of key points:

1. Introduction to Theory: Initially proposed after Alfred Wegener’s continental drift theory, Plate Tectonics gained traction due to advancements in geophysical techniques. Canadian geophysicist J. Tuzo Wilson formulated the concept in 1966.
2. Principles of Theory:
• Plates: Earth’s lithosphere consists of large, solid plates that move over the asthenosphere. These plates vary in thickness and interact at their boundaries.
• Movement of Plates: Each plate moves independently, driven by the plastic nature of the mantle and the accretion of material at mid-oceanic ridges.
3. Plate Boundaries: Interactions between plates occur at their boundaries, resulting in various geological phenomena such as earthquakes and volcanic activity.
• Convergent Boundaries: Plates collide, leading to subduction where one plate descends beneath another. This process generates volcanic arcs and mountain ranges.
• Divergent Boundaries: Plates move apart, creating rift valleys and mid-ocean ridges where new oceanic crust forms.
• Transform Boundaries: Plates slide past each other horizontally, causing earthquakes along deep faults. The San Andreas Fault is a well-known example.
Further Reading:  Centripetal Force [with MCQs]

Plate Tectonics provides a comprehensive framework for understanding Earth’s dynamic surface and its geological features. It explains phenomena like earthquakes, volcanic eruptions, and the formation of mountain ranges, enhancing our knowledge of the planet’s evolution and geology.