UPSC STATIC QUIZ – Geography : 9 April 2024

Solution: b)

Statement 3 is incorrect.

Just like an onion, Earth is made up of several concentric layers with one inside another. Earth’s uppermost layer is the crust, which is the thinnest of all the layers. On the continental masses, it is about 35 km and on the ocean floors only 5km.

Silica and alumina are the main minerals that constitute the continental mass, and are called sial (si, silica; al, alumina). Silica and magnesium are the main minerals that constitute the oceanic crust, and are called sima (si, silica; ma, magnesium).

Continental crust is less denser than ocean crust as the latter is made of basaltic rocks.

Core constitutes the innermost layer. Its radius is about 3500 km. Nickel and iron constitute the core, and it is called nife (ni, nickel; fe, ferrous, i.e. iron). The temperature and pressure at the central core are very high. It is the molten iron in core which gave rise to magnetic field of Earth.

Solution: b)

Statement 2 is incorrect.

Endogenic Forces

• Endogenic forces are those internal forces which derive their strength from the earth’s interior and play a crucial role in shaping the earth crust.
• Examples – mountain building forces, continent building forces, earthquakes, volcanism etc.
• The endogenic forces are mainly land building forces. The energy emanating from within the earth is the main force behind endogenic geomorphic processes. This energy is mostly generated by radioactivity, rotational and tidal friction and primordial heat from the origin of the earth.

Exogenic Forces

• Exogenic forces are those forces which derive their strength from the earth’s exterior or are originated within the earth’s atmosphere.
• Examples of forces – the wind, waves, water etc.
• Examples of exogenic processes – weathering, mass movement, erosion, deposition.
• Exogenic forces are mainly land wearing forces.

Solution: c)

• Paleomagnetism is the study of the record of the earth’s magnetic fieldwith the help of magnetic fields recorded in rocks, sediment, or archaeological materials.
• The polarity of the Earth’s magnetic field and magnetic field reversals are thus detectable by studying the rocks of different ages.
• Rocks formed from underwater volcanic activity are mainly basaltic (low silica, iron-rich) which makes up most of the ocean floor.
• Basalt contains magnetic minerals, and as the rock is solidifying, these minerals align themselves in the direction of the magnetic field.This locks in a record of which way the magnetic field was positioned at the time.
• Paleomagnetic studies of rocks have demonstrated that the orientation of the earth’s magnetic field has frequently alternated (geomagnetic reversal) over geologic time. Paleomagnetism led the revival of the continental drift hypothesis and its transformation into theories of Sea Floor Spreading and Plate Tectonics.

Solution: c)

The first detailed theory of continental drift was proposed by Alfred Wegener in 1912. With the help of large geologic and paleontological data, Wegener put forward that throughout most of geologic time period, there was only one continent, that is called Pangea. In the Triassic Period, Pangea got fragmented, and the parts began to separate and move from one another.

According to Wegener, the drift was in two directions:

1. Equatorwards due to the interaction of forces of gravity, pole-fleeing force (due to centrifugal force caused by Earth’s rotation) and buoyancy, and
2. Westwards due to tidal currents and this is because of Earth’s motion (According to Wegener, since Earth rotates from west to east, the tidal currents act from east to west).

Wegener suggested that tidal force (gravitational pull of Moon and to a lesser extent, Sun) also played a major role.

• The polar-fleeing force relates to the rotation of Earth. The shape of Earth is not a perfect sphere; there is a bulge at the equator. The rotation of Earth causes this bulge.

Solution: b)

Statement 1 is incorrect.

Block Mountains

• Block mountains are created because of faulting on a large scale (when large areas or blocks of earth are broken and displaced vertically or horizontally).
• The uplifted blocks are termed as horsts,and the lowered blocks are called graben.
• The Great African Rift Valley, The Rhine Valleyand the Vosges mountain in Europe are examples.
• Block mountains are also called fault-block mountainssince they are formed due to faulting as a result of tensile and compressive forces.