Which one of the following is not a major tectonic plate?
- (a)Saudi Arabian plate
- (b)Antarctica and the surrounding oceanic plate
- (c)India-Australia-New Zealand plate
- (d)Pacific plate
Correct — A, Saudi Arabian plate. There is no such plate. The other three options are copied word for word out of the NCERT list of the seven major plates in Class 11 Fundamentals of Physical Geography, chapter 4 — Antarctica and the surrounding oceanic plate, the India-Australia-New Zealand plate and the Pacific plate all sit in that numbered list, alongside the North American, South American, African and Eurasian plates. What the same page does with the Arabian landmass is put it among the MINOR plates, and its gloss reads 'Arabian plate : Mostly the Saudi Arabian landmass'. The examiner has taken that description and welded it into a plate name. The plate that exists is the Arabian plate; it covers about 5 million square kilometres, which is a quarter of the 20-million-square-kilometre floor conventionally used to separate major plates from minor ones.
- (b)Antarctica and the surrounding oceanic plate — This is major plate I on the NCERT list. It is the plate carrying Antarctica plus the ocean floor that rings it, and its almost entirely divergent boundaries are why Antarctica is being slowly pushed outward on all sides.
- (c)India-Australia-New Zealand plate — Major plate V on the same list. Textbooks also call it the Indo-Australian plate; its northern edge crashing into Eurasia is what raises the Himalaya, and its eastern edge produces the Java Trench.
- (d)Pacific plate — Major plate IV, and the largest of them all. It is almost wholly oceanic, and the subduction around its rim is what draws the Ring of Fire on a world map.
Plate tectonics divides the earth's lithosphere — crust plus the rigid top of the mantle, between about 5 and 100 km thick under the oceans and around 200 km under continents — into slabs that move over the plastic asthenosphere. NCERT counts seven major plates and then names a set of minor ones: Cocos, Nazca, Arabian, Philippine, and others such as the Caroline, Fiji, Juan de Fuca, Caribbean and Scotia plates. A plate is called continental or oceanic depending on which kind of crust makes up the larger part of it, so the Pacific plate is oceanic while the Eurasian plate is continental.
This is a recognition item, not a reasoning one, and it is decided entirely by whether you have read the NCERT list closely enough to notice which words it attaches to which category. The trap is well built, because 'Saudi Arabian plate' sounds plausible to anyone who half-remembers that there is an Arabian plate. The safeguard is the phrasing of the other three options: they are unmistakably NCERT's own wording, so the odd one out is the one that has been reworded. A second check is size. Major plates are the ones large enough to be drawn on a world map at a glance; a plate confined to one peninsula is by definition a small one.
- NCERT lists exactly seven major plates: Antarctica and the surrounding oceanic plate, North American, South American, Pacific, India-Australia-New Zealand, Africa with the eastern Atlantic floor, and Eurasia and the adjacent oceanic plate.
- The Arabian plate is listed as a minor plate, described in NCERT as 'mostly the Saudi Arabian landmass'.
- By the common convention a major plate has an area above 20 million sq km; the Arabian plate covers roughly 5 million sq km.
- The lithosphere is 5-100 km thick in oceanic areas and about 200 km in continental areas; plates ride over the asthenosphere.
- The theory took shape in 1967, when McKenzie and Parker and, independently, Morgan gathered the sea-floor-spreading evidence into the model now called plate tectonics.
- Reading a plausible-sounding plate name as real. The plate is the Arabian plate; 'Saudi Arabian plate' is only NCERT's description of where it lies.
- Counting the Indian plate and the Australian plate separately when the textbook treats them as one India-Australia-New Zealand plate.
- Assuming a plate must be either wholly continental or wholly oceanic — most carry both kinds of crust.
Almost always as an odd-one-out on the major-plate list, or as a match between a minor plate and the region it underlies.
Which of the following statements about Ring of Fire is/are correct ? 1. It is a zone of convergence plate boundaries 2. It is an active seismic and volcanic zone 3. It is associated with deep trench Select the correct answer using the code given below :
- (a) 1 and 2 only
- (b) 2 and 3 only
- (c) 1 only
- (d) 1, 2 and 3
Answer(d) 1, 2 and 3
The same plate map, read for what the boundaries do rather than for what the plates are called. Knowing that the Pacific plate is ringed by convergent boundaries, trenches and volcanoes is the reason it turns up on every list of major plates.
- practice — not a real PYQ
According to the NCERT classification, which one of the following is a minor plate?
- (a)Pacific plate
- (b)Nazca plate
- (c)Eurasian plate
- (d)African plate
Answer(b) Nazca plate — it lies between South America and the Pacific plate and is listed among the minor plates, while the other three are major plates.
- practice — not a real PYQ
The lithosphere, which is broken into tectonic plates, moves over which one of the following layers?
- (a)Outer core
- (b)Asthenosphere
- (c)Inner core
- (d)Barysphere
Answer(b) Asthenosphere — the plastic upper-mantle layer beneath the rigid lithosphere over which the plates slide horizontally.