Plate Tectonics — Set 3
Geography · प्लेट विवर्तनिकी · Questions 21–30 of 40
Who is the German meteorologist credited with the 'Continental Drift' theory?
Correct Answer: D. Alfred Wegener
Alfred Wegener proposed the Continental Drift theory in 1912. He suggested that all continents were once joined in a single landmass called Pangea. Fossil and geological similarities across oceans were the main pillars of his evidence.
Which plate boundary is known as a 'Constructive Boundary'?
Correct Answer: C. Divergent boundary
A divergent boundary is called constructive because new lithosphere is created as plates pull apart. Magma rises from the mantle to form new crust on the ocean floor or land. The process of sea-floor spreading is the primary example of this boundary.
A 'Destructive Boundary' is another name for which of the following?
Correct Answer: A. Convergent boundary
Convergent boundaries are called destructive because the Earth's crust is consumed or crumpled during collisions. In subduction zones, the sinking plate melts into the mantle and is destroyed. This process balances the creation of new crust at divergent boundaries.
The 'Mesosaurus' fossil was used as evidence for continental drift because it was found in which two continents?
Correct Answer: C. Africa and South America
Fossils of the freshwater reptile Mesosaurus were found only in South Africa and Eastern South America. Since it could not have swum across the salty Atlantic, it suggested the continents were once connected. This was a key biological proof for Alfred Wegener's theory.
Which layer of the Earth acts like a plastic or semi-fluid, allowing plates to move over it?
Correct Answer: D. Asthenosphere
The asthenosphere is the ductile part of the upper mantle located just below the lithosphere. It behaves plastically, allowing it to flow slowly over geological time. This characteristic enables the rigid tectonic plates to glide across it.
Island arcs, like the Aleutian Islands, are formed at which type of boundary?
Correct Answer: D. Oceanic-Oceanic convergence
Island arcs are chains of volcanic islands formed when one oceanic plate subducts under another oceanic plate. The melting subducting plate creates magma that rises to form underwater volcanoes. Eventually, these volcanoes grow tall enough to break the sea surface.
What is the typical rate of movement for tectonic plates per year?
Correct Answer: D. A few centimeters
Tectonic plates move at a very slow rate, typically 2 to 10 centimeters per year. This rate is roughly comparable to the speed at which human fingernails grow. Over millions of years, these small movements result in massive shifts in global geography.
Which major tectonic plate is almost entirely covered by oceanic crust?
Correct Answer: B. Pacific Plate
The Pacific Plate is the largest of the Earth's tectonic plates and is almost exclusively oceanic. It contains very little continental landmass compared to other major plates. Most of the plate is submerged beneath the Pacific Ocean.
In the context of plate tectonics, what is a 'Triple Junction'?
Correct Answer: A. The point where three tectonic plates meet
A triple junction is a geographical point where the boundaries of three tectonic plates meet. These junctions are complex areas with various combinations of ridges, trenches, and faults. The Afar Triple Junction in Africa is a well-known example.
Which of these is NOT a major tectonic plate?
Correct Answer: B. Nazca Plate
The Nazca Plate is considered a minor or intermediate tectonic plate, not one of the primary major plates. Major plates generally cover entire continents or vast ocean basins. There are seven or eight primary major plates recognized globally.