A continent is a large continuous area of land on the earth surface. Originally the continents were one big land mass known as Pangea.
Pangea surrounded by huge water mass known as Panthalassa. Due to conventional currents generated in the earth's mantle, Pangea split into two lands mass Laurasia and Gondwanaland.
There are separated by an East-West sea known as Tethys. Over millions of years Laurasia and Gondwana land split into various continents, Laurasia continued to drift resulting in the present day continents of North America, Europe, and Asia.
Gondwanaland drifted from South America, Africa and Madagascar, Australia, India, and Antarctica.
DISTRIBUTION OF CONTINENTS.
This is the largest continent found in Northern hemisphere running from 0° to 67°N and 67°E to 180°E
Its area is 42.2 million square kilometers. The continent is border by the Arctic Ocean to the North Pacific Ocean to the East and the Indian Ocean to the south. The Ural Mountains form the boundary between Asia and Europe. Asia is attached to Africa by the Suez now day to form Suez Canal.
Africa is the second largest continent covering an area of 30.3 million square kilometers. Africa extends from 30°S to 37°N of the Equator, making it an exceptional continent, crossed by major lines of latitude, the Equator 0°, the tropical of cancer 23½N and the Tropic of Capricorn 23½°S. It also extends from 17½°W to 50°E of Greenwich Meridian. Africa has two big deserts Sahara and the Namib Desert.
North America which occupies 24.0 million kilometers is the third largest continent.
It extends from 0°N to 65°N and from 60°W to 160°W. North America is bordered by the Pacific Ocean to the west by the Atlantic Ocean to the East and to the north by the Arctic Ocean.
South America is the fourth largest continent with an area of 17.4 million square kilometers.
It extends between 10°N and 50°S and from 35°W and 80°W. South America is about half the size of Africa. This continent is bordered to the East by the Atlantic Ocean, to the west by the Pacific Ocean and it joined to North America by the Isthmus of Panama.
Antarctica is the fifth continent in terms of Area. Its size is 11.4 million square kilometers.
It is situated in the Southern hemisphere within 66½°S
It is surrounded by the Southern Ocean. There are no permanent human residents.
Its temperature is below freezing point throughout the year making it impossible also the darkest place on the earth.
-Europe is the sixth continent in size with an area of 9.8 million square kilometers.
-It extends between 40°N and the Arctic Circle 66½°N and between 10°W and 60°E.
-It is bordered on the north by the Arctic Ocean, in the west by the Atlantic Ocean and in the South by the Mediterranean Sea.
This continent is found in the Southern hemisphere
It borders the Indian Ocean in the west and north the Pacific Ocean in the East and the Southern Ocean in South. It is made up of the Australian mainland, New Guinea, Tasmania and the intervening Islands.
With an area covering 8.6 million square kilometers, it is smallest of all continents.
MAJOR RELIEF FEATURES OF THE CONTINENTS.
The surface of a continent is not smooth. The term physical features refer to the height and shape of the land surface together with river, valleys, lakes and another water surface. There are many features found on the continent these include.
[*]Rivers and Valleys
A plateau is an extensive highland area with more or less uniform summit level.
Plateaus are usually bordered by a steep slope on one or more sides, Example of plateaus are the central plateau of Africa, the plateaus of Arabia, Tibet plateaus in Asia and the South African plateaus.
Plateaus can be formed by two ways
, as a result of forces operating in the crust that makes part of a plain area to be uplifted and another one to be depressed hence forming a plateau.
from fissure eruption which allows lava to outflow and spread over an extensive area.
-The Decan plateau, for instance, was formed as a result of fissure eruption.
These are extensive areas of almost flat land in the generally low elevation.
As stated earlier, they result when the land is depressed by downward movement of the crust. Example of plains Great central plains of North America, the North Europe plains and the Indo-Gangetic plains, Siberia in Asia.
River and Valleys
A river is a mass of water flowing indefinite channel to the sea, Lake Basin or a marsh. Some of the world's major river
Nile (Africa) about 6,670km long.
Amazon (South America) about 6500km long.
Mississippi (North America) about 6030km long.
Yangtze (China) about 5, 470km long.
Condo (Africa) about 4,820km long.
Volga (Russia) about 3,700km long.
In Tanzania, the main river includes Ruvuma, Rufiji, and Pangani. Water in rivers flows down a slope because of the forces of gravity. In its course, the river receives a number of small streams that pour water into it.
-These small streams are called tributaries.
The small branch of the river entering the Sea, Ocean or Lake is called distributaries.
The whole area drained by the river and its tributaries are known as the drainage basin.
The world known valley was formed through faulting caused by either compression or tensional force. In tensional faulting, layers of the crust are subjected to tensional force.
Hills are land forms with moderate relief of between 150 meters and 300 meters above the ground areas.
Mountains are land forms which have high relief that is heights over 300 meters above the surrounding areas.
Mountains may be formed in the following ways.
a) Folding b) Faulting c)The eruption of Volcano d) Changes in the level of the land or sea.
These are formed when layers of sedimentary rocks are gradually pushed in wards from either side by compressional force.
Example of Fold mountains are Atlas mountains of West Africa, Cape range of South Africa, Himalayas of India, The Rock mountains of Northern America, The Andes of South America and The Appalachian in the U.S.A
These are formed by Faulting of the crustal rocks. Faulting is the fracturing or breaking of crustal rocks, two forces that are tensional and compressional forces may lead to the formation of Block Mountains.
Example of block Mountains is Pare and Usambara which are both from Tanzania, Ruwenzori in Uganda.
These are the mountains which are formed due to the piling up and cooling of the hot molten lava and ashes that are thrown out from the earth’s interior during a volcanic eruption. Examples of the volcanic mountain are Kilimanjaro, Fujiyama in Japan, and Oldonyo lengai in Tanzania.
Types of the volcanic mountain.
- Active volcanic mountain;
These are the mountains which experience periodic eruption example Nyarugongo in the democratic republic of Congo and Oldonyo lengai in Tanzania.
- Dormant volcanic mountain
These are mountains which are not currently erupting but are likely to do so in future example Kilimanjaro.
- Extinct volcanic mountain
These are mountains which erupted once and there is no sign of erupting again. Example mounts Kenya, Elgon in Kenya, Ngorongoro and Rungwe in Tanzania.
These are the mountains formed as a result of the action of weathering which breaks the rocks and erosion by torrential rains, winds and moving ice which remove all the weathered material on the high land.
Example of residual mountains includes Taita hills, Sekenke hills of Singida, Adamawa mountain of Eastern Nigeria.
The large part of the earth is covered by water which forms 75%. This forms a connected expanse divided into oceans and seas. Other water bodies include lake and rivers.
The ocean is a large body of water on the earth surface. The large part of this water bodies lies in the southern hemisphere. The following are the oceans of the world the Indian, the Pacific Ocean, the Atlantic Ocean, the Arctic and the Southern Ocean.
- The Pacific Ocean.
This is the largest or greatest of all oceans and covers a third of the earth’s surface.
It is about 179.7 million square kilometers. Its basin contains some of the greatest known depths
The water of Pacific Ocean forms the western coast of both North and South America and the eastern coasts of Asia and Australia. There are numerous islands in this Ocean.
- The Indian Ocean.
The Indian Ocean is bordered by Africa on the west India and China on the north and Australia and East Indies on the east.
It is the third largest body of water in the world. Its cover about 20% of earth’s surface, its areas is about 73.5 million square kilometers.
- The Atlantic Ocean.
This is the second largest Ocean. It covers about one-fifth of the earth surface.
It is about 82.4 million square kilometers,
It is bordered to the west side by North and South America of Gibraltar leading to the Mediterranean Sea.
- The Southern Ocean.
This is the body of water that encircles the continent of Antarctica.
It is the world’s fourth largest Ocean, it covers about 20.3 million square kilometers.
- The Arctic Ocean.
The Arctic Ocean is 14.0 million square kilometers.
It lies to the north of North America and Eurasia.
North Ward the Arctic Ocean extends across the frozen Seas surrounding the North Pole to the Pacific with which it is linked by the bearing straight.
It is smallest of the world’s five Ocean and the shallowest.
Features of the oceanic floor.
The relief of the Ocean floor is as varied as that of the land surface. These major relief features of the ocean floor are A) Continental shelves B) Continental slopes C) Ridges D) Ocean deeps E) Deep sea plains F) Islands.
- Continental shelves
: - Are the gentle slope margins of the continents that form the shallow areas of Oceans. They extend to a depth of 200 meters they vary in which from place to place some continental shelves have Islands.
- Continental slopes
-A continental slope is found where the continental shelf drops abruptly forming steep slope towards the ocean.
- Ocean Ridges
-Oceanic ridge is raised part of the ocean floor. It takes the form of a ridge or plateau, ridge form at the extension boundary where the crustal rocks are being pulled.
- Ocean Deeps or trenches
-These are steep-sided long, narrow depressions on the ocean floor. Example Mariana trench, Atacama, Mindanao at Pacific
-They can reach a depth of 10,000m or more.
- Deep Sea plains
-There are the most extensive areas of the Ocean floor. A Large part of these plains is covered with fine mud.
-There are many islands in oceans and sea that are formed through various processes. The most common are formed by marine erosion when it occurs headland is eroded and isolated rock out crops are formed.
-Example Pemba and Zanzibar, Lamu and mafia.