The Earth is covered by waterWhich occupies 71 percent and land that occupies 29 percent of the Earth’s Surface. The surface of the Earth is not even, because it has lofty mountains, Deep oceans and other landforms Continents and oceans are grouped as First order landforms. The vast land masses On Earth are called Continents and huge Water bodies are called Oceans. There are seven continents. They are Asia, Africa, North America, South America, Antarctica, Europe and Australia. Asia is the largest continent, whereas Australia Is the smallest one.

Apart from continents, there are five Oceans located on the Earth’s surface. They are the Pacific, Atlantic, Indian, Southern and Arctic Oceans. Among These oceans, the Pacific Ocean is the Largest and the Arctic Ocean is the smallest.

Pacific Ocean:

The Pacific Ocean Is the largest and Deepest ocean on the Earth. It covers about One-third of the Earth Total area and spreads for about 168.72 Million sq.km. It is bounded by Asia and Australia in its west and North America And South America in its east. It stretches From the Arctic Ocean in the north to the Southern Ocean in the south.

This ocean’s shape is roughly Triangular with its apex in the north at The Bering Strait which connects the Pacific Ocean with the Arctic Ocean. The Bering Sea, the China Sea, the Sea of Japan, Tasman Sea and the Philippine Sea are some of the marginal seas of the Pacific Ocean. Indonesia, Philippines, Japan, Hawaii, New Zealand are some Of the islands located in this Ocean. The deepest point Mariana Trench is 10,994 m- and is located in the Pacific Ocean. A chain of volcanoes is located Around the Pacific Ocean called the Pacific Ring of Fire.

Atlantic Ocean:

The Atlantic Ocean is the second Largest ocean on Earth. It covers one sixth Of the Earth’s total area and spreads for About 85.13 million sq.km . It is bounded By North America and South America in The west and Europe and Africa in the East. Like the Pacific, it stretches from The Arctic Ocean in the north to the Southern Ocean in the south. The shape Of the Atlantic Ocean resembles the letter ‘S’. The Strait of Gibraltar connects the Atlantic Ocean with the Mediterranean Sea. The Atlantic Ocean is the busiestShipping route between the Eastern and Western hemispheres. The deepest point Is the Milwaukee Deep in the Puerto Rica Trench. It has a depth of about 8600 m-. The Caribbean Sea, the Gulf of Mexico, The North Sea, the Gulf of Guinea and the Mediterranean Sea are important margina Seas of the Atlantic Ocean. St. Helena, Newfoundland, Iceland and Falkland are Some of the islands found in this ocean.

Indian Ocean:

The Indian Ocean is the third largest ocean On the Earth’s surface. It covers an area of About 70.56 million sq.km. It is named after India. It is triangular in shape and bounded By Africa in the west, Asia in the north and Australia in the east. The Andaman and Nicobar Islands, Lakshadweep, Maldives, Sri Lanka, Mauritius and the Reunion Islands Are some of the islands located in the Indian Ocean. Malacca strait connects the Indian Ocean and the Pacific Ocean.The Bay of Bengal, the Arabian Sea, the Persian Gulf and the Red Sea are some of The important marginal seas of the Indian Ocean. The Java trench (7,725m-) is the Deepest point in the Indian Ocean.

1. Palk Strait connects the Bay of Bengal and Palk Bay.
2. 6° Channel Separates Indira Point and Indonesia
3. 8 Channel separates Maldives And Minicoy islands
4. 9° Channel separates Lakshadweep Islands and Minicoy Islands
5. 10° Channel separates Andaman And Nicobar Islands

Southern Ocean:

The Southern Ocean surrounds the Continent of Antarctica and is enclosed By the 60°S latitude. It covers an area of 21.96 million sq.km. It is bordered by the Southern parts of the Pacific, the Atlantic and the Indian Oceans. The Ross Sea, the Weddell Sea and the Davis Sea are the Marginal seas of this Ocean. Farewell Island, Bowman Island and Hearst Island are some of the islands located in this ocean. The Water in this ocean is very cold. Much ofIt is covered by sea ice. The deepest point in this ocean is South Sandwich Trench with a depth of 7,235 m-

Arctic Ocean:

The Arctic Ocean is the smallest ocean. It covers an area of 15.56 million sq.km. It lies within the Arctic Circle. It remains Frozen for most of the year. The Norwegian Sea, the Greenland Sea, the East Siberian Sea and the Barents Sea are some of the Marginal seas of this ocean. Greenland, New Siberian Island and Novaya Zemlya Island are some of the islands located In the Arctic Ocean. The North Pole is situated in the middle of the Arctic Ocean. The Eurasian Basin is the deepest Point in the Arctic Ocean, which is above 5,449 m- In depth.

Island: A land Surrounded by Water on all Sides.

1. Bay – A broad inlet of The Sea where the land curves inwards.
2. Strait – A narrow stretch of water linking two large water Bodies.
3. Trench – The deepest part of the ocean.
4. Peninsula – The land Surrounded by Water on three Sides.

One of the most indispensable natural Resources on earth is water. The Earth is also called the Blue planet, as it holds water in Abundance and thus stands unique among all other planets. Hydrosphere consists of water in various forms found on the earth. Over 97% of the water on the Earth’s surface is confined to Oceans. Less than 3% of water is held on landas glaciers, ice caps, groundwater, rivers, lakes, And also as the water vapour in air.

 Hydrological Cycle:

The Earth’s water is not static. It is always in Motion. This continuous Movement of water on, above and below the Earth’s surface is called The Hydrological Cycle.

The three major processes involved in the Water cycle are evaporation, condensation and precipitation. Water changes its form constantly i.e. Ice, water and water vapour. This process happens in the blink of an eye Or even over millions of years.Water resources of the Earth can be broadly Divided into fresh water and salt water.

Fresh Water:

Rain water is considered to be the purest Form of water, as it contains very less proportion Of salts when compared to the oceans andSeas.In the form of ice caps and glaciers. Around 1% of it is found in the liquid state as rivers, Streams, lakes, ponds etc. Surface water may Also penetrate through porous rocks and gets Collected beneath the Earth’s surface. This is Called groundwater.

Finland is known as the land of thousand Lakes. There are 1,87,888 lakes in Finland.

Water table is a level below the Ground, where water is found Collected beneath the Earth’s Surface.

Aquifers are porous rock Strata filled with water, found below the Earth’s surface.

Oceans:

The continents and oceans are however, Not evenly distributed in the northern and The southern hemispheres. The northern Hemisphere holds 61% of land whereas the Southern hemisphere holds 81% of water. It Is because of this pattern of land and water Distribution, the northern hemisphere is Called as the land hemisphere and theSouthern hemisphere is called as the water Hemisphere.

Oceans and seas are considered as resource Bowl of the earth because of the immense Availability of food, minerals etc., Present Distribution of the world’s oceans and major Seas

Relief of the Ocean Floor:

The ocean basins are Characterised by the following

Major relief features:

1. Continental shelf
2. Continental slope
3. Continental rise
4. Deep sea plain or Abyssal plain
5. Oceanic deep
6. Oceanic ridge

Continental Shelf:

A shallow and gently sloping platform extending Out from the adjoining continental land mass into The sea is called Continental Shelf. It is almost a Uniform zone of sea bed with a gentle gradient.

The continental shelf is of great significance for the following reasons:

1. They are shallower, thus enables sunlight to Penetrate through the water. This encourages Abundant growth of grass, sea weeds and Plankton. Hence these zones become the Richest fishing grounds in the world. Eg. The Grand Banks of Newfoundland.
2. The continental shelves have extensive Deposits of minerals and mineral fuels. Hence, this zone becomes accessible for Oil drilling and mining activities. E.g. Mumbai High in Arabian Sea.

Continental Slope:

A steep slope which descends from the edge of The continental shelf to the deep ocean-bed is Called continental slope. It forms a boundary Between the Continental Crust and the oceanic Crust. This zone is free from deposits as they Are steep. The most important characteristic Of continental slope is the presence of deep Canyons and trenches. Due to the low Penetration of sunlight, the slope has nearly Freezing temperature. Hence aquatic life has Very slow rate of metabolism.

Continental Rise:

At the base of the continental slope is a gently sloping Layer of sediments which merge into the deep-Sea floor. This underwater feature found between Continental slope and abyssal plains is called the Continental rise. It consists of submarine fans Which are similar to the alluvial fans found on land.

Deep Sea Plains or Abyssal Plains:

The deep sea plains or abyssal Plains are underwater plains Found on the deep ocean floor. These plains extend from Continental rise to the mid Oceanic ridges. The gradient Of the slope is very gentle and It appears as a uniform flat and featureless plain. These plains are usually covered by the thick layer Of sediments composed of clay, silt and sand, Brought by the rivers. These are often characterized By features like abyssal hills, sea mounts, guyots, Coral, atoll etc.

Abyssal plains in the Atlantic And Indian Oceans tend to Be extensive than the Pacific Oceans because, majority Of the world’s largest rivers Empty their sediments into either Atlantic Or Indian Ocean. E.g. Amazon, Ganga and Brahmaputra rivers.

Oceanic Ridge:

Oceanic ridge is a continuous submarine Mountain chain. They are made of young basaltic rock formed when two tectonic plates Moves apart. The mid-ocean ridge is probably The most extensive single feature of the earth’s Topography. Two of the most well known mid-Ocean ridges are the Mid-Atlantic Ridge and the East Pacific Ridge. The Mid-Atlantic Ridge is The largest unbroken oceanic ridge.

Fathoms:

A nautical Measurement of the depth of Water in the ocean.

Isobath:

An imaginary line On a map joining the points of equal depths.

Isohaline:

An imaginary line on a map Joining the points of equal salinity in oceans.

Movement of the Ocean Water:

The ocean water is dynamic. Temperature, Salinity, density, external forces of the sun, Moon and the winds keep the ocean waters in Movement, both horizontally and vertically. Waves and currents are in horizontal motionWhile tides have vertical motion.

Waves:

All the movements of the oceans, sea waves are considered to be the strongest. Sea waves are Ripples on water caused when winds blow over the sea. The height of these waves depends on the speed of wind, its duration and the direction from which they blow. Sometimes waves are also caused by tremors felt on the ocean floor. Such Waves are quite destructive and called Tsunami.

Tides:

The periodic rise and fall of sea water due To the gravitational pull of the sun and moon On earth are called tides. They are classified Broadly into Spring tides and Neap tides.When the Sun, Moon and Earth are aligned In the same line, the collective gravitation pull of The sun and moon on earth’s water strengthens to Form a high tide known as spring tide. Such tides Always occur on full moon and new moon days 

When the sun and the moon are at right Angles, their gravitational forces work against Each other, causing a low tide called neap tide. A neap tide occurs between two spring tides i.e., Twice a month, when the first and last quarter Moon appears.

Oceans Currents:

The movement of oceanic water on the Surface and at the depths in a definite direction is called ocean current. Ocean currents are in clockwise motion in the northern hemisphere and in the anti-clockwise motion in the southern Hemisphere.

The factors that generate ocean currents are:

1. Earth’s rotation
2. Prevailing winds and
3. Differences in temperature and salinity of Ocean water.

On the basis of temperature, ocean currents Are classified as warm currents and coldCurrents. The movement of ocean currents From the high latitudes (temperate and Polar zones) towards low latitudes (tropical Zones) is called cold current. Eg. Labrador in Atlantic Ocean and Peruvian cold current in South Pacific Ocean.