MAINS DAILY QUESTIONS & MODEL ANSWERS
Q1. Though local salinity patterns are largely determined by rainfall and evaporation, the salinity of the oceans is determined globally by a number of factors. Evaluate. (250 words)
Paper & Topic: GS I à Geography
Model Answer:
Introduction:
- The entire content of dissolved salts in sea water is referred to as salinity.
- The amount of salt (in gm) dissolved in 1,000 gm (1 kg) of saltwater is used to calculate it.
- At 0 degrees Celsius, the salinity of ocean water is normally around 35 parts per thousand.
- This means that dissolved salts account for 3.5 percent of the total weight of ocean water.
- The most prevalent dissolved salt in the sea is sodium chloride, sometimes known as common salt.
Body:
Salinity is influenced by a number of factors, including:
- Controlling variables of oceanic salinity are elements that influence the quantity of salt in different oceans and seas.
- Evaporation: Evaporation determines the salinity of water in the ocean’s surface layer. Salinity is higher where evaporation is greater, as as in the Mediterranean Sea.
- Inflow of freshwater:Freshwater flow from rivers has a big impact on surface salinity in coastal areas, while ice freezing and thawing has a big impact in polar regions.
- Where there is a higher flow of freshwater into the oceans, the salinity is lower.
- The ocean surface salinity in the mouths of rivers like the Amazon, Congo, and Ganga, for example, is found to be lower than the average surface salinity.
- Temperature and density: Water’s salinity, temperature, and density are all linked. As a result, any change in temperature or density has an impact on an area’s salinity.
- In general, places with high temperatures also have high saline levels.
- Ocean currents: They influence the spatial distribution of dissolved salts in ocean waters.
- Warm currents near the equator push salts away from the ocean’s eastern boundaries, where they collect near the western margins.
- In temperate locations, ocean currents enhance the salinity of ocean waters near the eastern edges. For example, the Gulf Stream in the North Atlantic Ocean raises the salinity of ocean waters around the Atlantic Ocean’s western edges.
Precipitation: There is an inverse link between precipitation and salinity.
- In general, regions with higher precipitation levels have lower salinity levels.
- This is why, although being as hot as the subtropics, the equatorial region has lower salinity than the subtropics because the former receives more precipitation each day.
Wind direction and atmospheric pressure: anti-cyclonic circumstances with steady air and high temperatures increase the salinity of ocean surface water.
- Winds aid in salinity redistribution by driving saline waters away from more saline locations, resulting in a decrease in salinity in the former and an increase in the latter.
Conclusion:
- The density of saltwater, as well as its vertical flow patterns in thermohaline circulation, is determined by salinity and temperature.
- Around 3 billion tonnes of salt are introduced to the oceans each year from the land.
- Humans remove only a small portion of this salt for everyday ingestion.
Q2. Plate tectonics explains why the Earth’s continents are shifting, whereas continental drift theory did not. Elaborate. (250 words)
Paper & Topic: GS I à Geography
Model Answer:
Introduction:
- Continental drift is one of the first theories on how continents moved over time, according to geologists.
- It was a theory that explained how various forces on the Earth’s surface cause continents to shift position on the surface.
- The lithosphere, the Earth’s solid outer crust, is divided into plates that move across the asthenosphere, the molten upper layer of the mantle, according to plate tectonics theory.
- Oceanic and continental plates collide, spread apart, and interact at all of the planet’s boundaries. The study of plate tectonics has largely supplanted the hypothesis of continental drift today.
Body:
- Continental drift: The scientist Alfred Wegener is most closely identified with the hypothesis of continental drift. Wegener released a paper in the early twentieth century describing his notion that continental landmasses were “drifting” across the Earth, occasionally plowing through oceans and colliding with one another. He coined the phrase “continental drift” to describe this trend.
Pangaea:
- Wegener believed that the Earth’s continents were once part of a massive landmass known as
Pangaea:
- Pangaea began to break apart into two smaller continents, Laurasia and Gondwanaland, during the Jurassic period, some 200 to 130 million years ago, according to Wagener’s theory.
- The fact that the continents of South America and Africa fit together like jigsaw puzzle pieces, that fossil remains of the same extinct animal or plant can be found across numerous continents, and that identical rocks can be found on both sides of the Atlantic Ocean inspired his theory. These rocks were of the same sort and age, indicating that they were deposited by prehistoric glaciers.
- Wegener’s theory of continental drift was rejected by scientists. The mechanism for how it works, why did the continents drift, and what patterns did they follow, were all missing from the hypothesis.
- Plate tectonics: Wegener’s hypothesis later helped to establish the theory of plate tectonics, but scientists did not believe that continents could move when Wegener was alive.
- Tectonic plates are huge slabs of rock that support continents. Plate tectonics is a process in which plates constantly move and interact.
- Plate tectonics is a theory that explains how the earth’s outer crust, or lithosphere, moves. Tectonic plates divide the lithosphere. Convective forces generated within the asthenosphere, powered by the earth’s core’s internal heat, cause the crust to shift.
Why plate tectonics is better than continental drift theory:
- Plate tectonics explains the mechanism of tectonic plate motion, whereas continental drift theories leaves the topic unsolved.
- Tectonic plates have been moving around the globe continuously throughout the earth’s history. Wegener was incorrect in his assumption that the continent moved. Continents are part of a plate, and the plate travels.
- Wegener believed that all of the continents once existed as a single supercontinent known as Pangaea. Later discoveries demonstrate, however, that the continental masses lying on the plates have been traveling throughout the geological period, and Pangaea was the result of the convergence of separate continental masses that were components of one or both plates.
- Most scientists thought the earth was a solid, immovable substance when Wegener developed his idea of continental drift. Concepts of sea floor spreading and the unified theory of plate tectonics, on the other hand, have emphasized that both the earth’s surface and its interior are dynamic, not static and immovable.
Spreading of the seafloor:
- Underneath the solid plates, the movable rock is thought to be moving in a circular motion. The heated material rises to the surface, spreads, and cools before sinking back into deeper levels. This cycle is repeated several times to produce a convection cell or convective flow, as scientists name it.
- The finding of “magnetic stripes” on the seafloor later in the 1960s provided the last proof: magnetic domains in marine rocks recorded the reversal of Earth’s magnetic field over time. The pattern was symmetrical to the ridge, implying that the seafloor was spreading in a symmetrical manner. The concept of subduction zones was conceived.
- Plate tectonics is a theory that explains Wegener’s observations and how lithosphere can be produced and consumed in such a way that the Earth’s size remains constant.
- The continental drift theory of Wegener lacked a driving motor. Other scientists were curious as to what was causing these continents to shift. Wegener, unfortunately, was unable to produce a persuasive response. The accumulation of major evidence presently underlying modern plate tectonic theory was made possible by technological improvements necessary by the Second World War.
The following two forces are insufficient to effect change:
- The spinning of the Earth on its own axis produces a centrifugal force, which is a force directed away from the axis of rotation and towards the equator. Wegener theorized that the planet’s centrifugal force broke up the supercontinent and pushed continents away from the poles toward the equator. As a result, he coined the term “pole-fleeing or centrifugal force” to describe this drifting mechanism.
- Wegener attempted to trace the Americas’ westward drift to lunar-solar drag, i.e., the gravitational influences of the sun and moon, by invoking tidal force.
- He also recognized that the travel of continents is most likely caused by pole-fleeing or centrifugal force, as well as tidal force. Wegener was unable to create a reliable system for the movement of continents. The most challenging problem for Wegener to tackle was the drifting mechanism.
- Plate tectonics is a major unifying geoscience theory that describes how continents move.
- Most significant characteristics on Earth’s surface, such as mountain construction, development of new lithosphere, consumption of old lithosphere, and mid-ocean ridges, are caused by earthquakes and volcanism.
Conclusion:
- The hypothesis of continental drift was scientifically proven in the form of plate tectonic theory after approximately 60 years.
- Finally, it provided a new perspective on the global distribution of earthquakes and volcanoes, as well as the identification of disaster-prone locations.
