General Knowledge for SSC Exams (Some Important Facts)

General Knowledge for SSC Exams (Some Important Facts) 

  • The total surface area of the earth
510,067,2000 sq. km.
  • Total area covered by water or sea
70.92%
  • The land area
29.08%
  • The equatorial circumference of the earth
40,075,03 km.
  • The meridional circumference
40,007,89 km.
  • The total world’s population
6.25 billion (Approximately)
  • The average daily increase in the world’s population
263,000 (182 per minute)
  • The crude birth rate
27.1 per 1000
  • The crude death rate
9.8 per 1000
  • The most populous country
China
  • The least populous country
Vatican city
  • Most densely populated country
The Portuguese province of Macau
  • Total number of countries
253
  • The largest country in area
Russia
  • The smallest country in area
Vatican city
  • The most populous city
Mexican city
  • The largest City
Mount Isa, Queensland, Australia

Isostacy

One interesting property of the continental and oceanic crust is that these tectonic plates have the ability to rise and sink. This phenomenon, known as isostacy, occurs because the crust floats on top of the mantle like ice cubes in water. When the Earth’s crust gains weight due to mountain building or glaciation, it deforms and sinks deeper into the mantle. If the weight ‘is removed, the crust becomes more buoyant and floats higher in the mantle. This process explains recent changes in the height of sea-level in coastal areas of eastern and northern Canada and Scandinavia. Some locations in these regions of the world have seen sea-level rise by as much as one meter over the last one hundred years. This rise is caused by isostatic rebound. Both of these areas where covered by massive glacial ice sheets about 10,000 years ago. The weight of the ice sheets pushed the crust deeper into the mantle. Now that the ice is gone, these areas are slowly increasing in height to some new equilibrium level.

Lithosphere

The word lithosphere is derived from the word sphere, combined with ‘the Greek word lirhos. meaning rock. The litho-sphere is the solid outer section of Earth, which includes Earth’s crust (the “skin” of rock on the outer layer of planet Earth), as well as the underlying cool, dense, and rigid upper part of the upper mantle. The lithosphere extends from the surface of Earth to a depth of about 44-62 mi (70-100 km). This relatively cool and rigid section of Earth is believed to “float” on top of the warmer, non-rigid, and partially melted material directly below.

Earth is made up of several layers. The outermost layer is called Earth’s crust. The thickness of the crust varies. Under the oceans, the crust is only about 3-5 mi (5-10 km) thick. Under the continents, however, the crust thickens to about 22 mi (35 km) and reaches depths of up to 37 mi (60 km) under some mountain ranges. Beneath the crust is a layer of rock material that is also solid, rigid, and relatively cool, but is assumed to be made up of denser material. This layer is called the upper part of the upper mantle, and varies in depth from about 31-62 mi (50-100 km) below Earth’s surface. The combination of the crust and this upper part of the upper mantle, which are both comprised of relatively cool and rigid rock material, is called the lithosphere. Below the lithosphere, the emperature is believed to reach 1,832°F (1,000°C), which is warm enough to allow rock material to flow if pressurized. Seismic evidence suggests that there is also some molten material at this depth (perhaps about 10%). This zone which lies directly below the lithosphere is called the asthenosphere, from the Greek word asthenes, meaning weak. The lithosphere, including both the solid portion of the upper mantle and Earth’s crust, is carried “piggyback” on top of the weaker, less rigid asthenosphere, which seems to be in continual motion. This motion creates stress in the rigid rock layers above it, forcing the slabs or plates of the lithosphere to jostle against each other, much like ice cubes floating in a bowl of swirling water. This motion of the lithospheric plates is known as plate tectonics, and is responsible for many of the movements seen on Earth’s surface today including earthquakes, certain types of volcanic activity, and continental drift.

Hydrosphere

Hydrosphere is the name given to all the water of the Earth in solid, liquid and gaseous forms. It thus includes the water of the atmosphere, water on the Earth’s surface (e.g. oceans, rivers, ice-sheets and ground water). Oceans, which are interconnected, cover about 70.8 per cent of the surface of the Earth. Pacific Ocean, which is the largest among the oceans, sprawls over an area of about 16,57,60,000 sq km, an area which is more than the total combined area of all the continents.

The oceans have an average depth of 3.5 km but their depth varies from place to place. The deepest known point is the Challenger Deep, a part of the Mariana Trench in the Pacific Ocean, which is 11.776 km deep.

The water in the oceans totals over 1,300 million cubic km, which is more than 97 per cent of world’s total water. The balance of water resources are contributed by glaciers, ice and snow, fresh water lakes, rivers and the underground water. The ocean floor consists of three main zones, viz., the continental shelf, the continental slope and the abyss. The continental shelves are, in fact, the submerged parts of the continents that gentally slope into the oceans bordering these continents.

The true edge of the continents is, however, the continental slope which begins from the point where the continental shelf ends. The abyss contains large sediment covered plains below the oceans. These plains are often interspersed by lofty volcanic mountains some of which surface as islands and long broad ridges which are in some places 2 to 4 kilometres high and up to 4,000 kilometres wide. The abyss also contains yawning chasms called deep sea trenches.

Continental Shelf (Littoral) is the sea bed bordering the continents, which is covered by shallow water up to about 100 fathoms (600 feet) beyond which is the continental slope.

Continental Slope is the region of the sea extending next to the continental shelf and having a depth up to 2,000 fathoms.

Continental Drift is a theory or hypo­thesis that continents have moved relative to each other across the surface of the earth. The idea was originally put forth by Antonio Snider-Pellegrini in 1858 and developed by the German geologist Alfred Wegner from 1910. He started that there was just one supercontinent, Pangaea which began to break up about 200 million years ago, since then the continents have drifted to their present positions.

Isohaline is the line which joins, on a.map points of the sea/oceans having equal salinity.

Ocean Current is the movement of a sizeable body of water as a current for fairly long distances along a specific path. It is known as ‘drift current when caused by the winds and as ‘convection current’ when brought about by variations in temperature. A ‘warm current’ is the one which flows from a warm to a cold region. The current flowing from a cold to a warm region is called a ‘cold current’.

Stream refers to any body of running water that flows on or under the surface of the water.

Swamp is a portion of wet, waterlogged or flooded land.

Spring Tides are caused as a result of the Moon and the Sun pulling the Earth gravitationally in the same direction. They occur twice a month around full moon and new moon.

Neap Tides are caused when the Moon and the Sun pull the Earth gravitationally in opposite directions. They occur twice a month during first and last quarters of the moon, when Sun, Earth and Moon are at right angles.

Lagoon is a shallow stretch of Water which is partly or completely separated from sea by a narrow strip of land. Reef is a ridge of submerged rock or other hard substance in sea water. It becomes visible at low tides.

Coral Reef is a ridge of coral and other organic materials consolidated into lime stone lying near the sea level. Bay is a wide curving indentation in a coastline lying between two head lands. Atoll is a circular or horse shoe shaped coral enclosing within it a lagoon. Fjord is a shallow stretch of river that may be crossed on foot or in a vehicle, commonly found in Norway or Sweden. Strait is a narrow sea passage that links two, large areas of sea, for example, the Strait of Gibraltar.

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