Question.2. Answer the following questions in about 30 words.

(i) Why do we call the earth a Blue Planet?
Answer. Water covers 71% of the earth’s surface. Because of this, life is conceivable on earth. Water is essential for all living things to survive. Therefore, it might be claimed that life is fortunate to exist on a world with water. Our planet is known as the “Blue Planet” because it has a lot of water on its surface.

(ii) What is continental margin?
Answer. One of the main ocean floor zones is the continental margin. It is a broad section of the continental shelf and slope that is inhabited by gulfs and rather shallow waters. The shallowest area of the ocean is along the continental margin. The slope has a gradient of just one degree or even less then 10 degree.

(iii) List out the deepest trenches of various oceans.
Answer. As many as 57 deep tranches have been explored so far. Out of these trenches 32 are in the Pacific oceans, 19 in the Atlantic Ocean and 6 in the Indian Ocean.

Some of the deepest trenches are as follows:

Oceans → Trenches
Pacific Ocean → Marina trench
Pacific Ocean → Challenger deep
Indian Ocean → Java

(iv) What is thermocline?
Answer. The temperature of the ocean water drops with depth, according to the temperature-depth profile of the water. Thermoclines are the edges of an area where temperature rises quickly. This layer stretches hundreds of metres downward and starts between 100 and 400 metres below the surface of the ocean.

(v) When you move into the ocean what thermal layers would you encounter? Why the temperature varies with depth?
Answer. When we move into the oceans we would encounter three layers from surface to bottom.

1. The first which is a top layer of the warm ocean water, is about 500 m thick, with the temperature 20 degrees to 25 degree centigrade.
2. The second layer is thermocline layer, which is 500 to 1000 thick and experiences the rapid decrease in temperature with increase in depth.
3. The third layer extends up to the deep ocean floor and is very cold. The sun’s rays fall directly over the equator and slant on the poles, causing a drop in temperature from the equator to the poles. Due to the distribution of land and water, the oceans in the northern hemisphere record relative temperatures that are greater than those in the southern hemisphere.

(vi) What is salinity of sea water?
Answer. The entire amount of dissolved salt in saltwater is known as salinity. The amount of salt (in grammes) dissolved in one kilogramme (1000g) of water is how it is calculated. It is a crucial characteristic of seawater. It varies according on sea depth. While the loss or import of water affects salinity at the sea’s surface, the salinity at the sea’s bottom does not change.

Question.3. Answer the following questions in about 150 words.

(i) How are various elements of the hydrological cycle interrelated?
Answer. Hydrological cycle is the cyclic movement of water containing basic continuous processes like evaporation, precipitation and runoff. Cycle begins with Runoff then evaporation will start, then after Precipitation occurs then again Runoff. This is a continuous cycle which starts with evaporation from the water bodies such as oceans.

Process of hydrological cycle starts with oceans. Water in oceans, gets evaporated due to heat energy provided by solar radiation and forms water vapour. This water vapour moves upwards to higher altitudes forming clouds. Most of the clouds condense and precipitate in any form like rain, hail, snow, sleet. And a part of clouds is driven to land by winds. Precipitation, while falling to the ground, some part of it evaporates back to atmosphere.

(ii) Examine the factors that influence the temperature distribution of the oceans.
Answer. The factors that influence the temperature distribution of oceans are:

1. Latitude: The temperature of oceans water decreases from the equator to the Poles. As the Sun’s rays become more and more inclined, the amount of insolation decreases.
2. Unequal distribution of land and water: Oceans in the Northern hemisphere receive more heat due to their constant contact with larger extent of land whereas oceans in the southern hemisphere receive less heat due to less presence of land masses in the this
   hemisphere.
3. Prevailing winds: The winds blowing from the land towards the ocean displace warm surface water away from the coast resulting the cold water from below to come up. It results into the longitudinal variation in temperature. This upwelling of water decreases the temperature. Due to upwelling of water by trade winds temperature is lower on the eastern than on the Western coast. Whereas, the onshore winds pile up warm water near the coast and this raises the temperature.
4. Ocean currents: The ocean currents maintain the temperature of the oceans. Warm ocean currents increase the temperature in cold areas where as the cold current decreases the temperature in warm areas. For example: Gulf Stream which is a warm current raises temperature near the eastern coast of the North America and the West coast of Europe. Whereas the Labrador current which is a cold current lowers the temperature near the north- east coast of North America.