Africa , second largest continent (2009 est. pop. 1,010,000,000), c.11,677,240 sq mi (30,244,050 sq km) including adjacent islands. Broad to the north (c.4,600 mi/7,400 km wide), Africa straddles the equator and stretches c.5,000 mi (8,050 km) from Cape Blanc (Tunisia) in the north to Cape Agulhas (South Africa) in the south. It is connected with Asia by the Sinai Peninsula (from which it is separated by the Suez Canal) and is bounded on the N by the Mediterranean Sea, on the W and S by the Atlantic Ocean, and on the E and S by the Indian Ocean. The largest offshore island is Madagascar; other islands include St. Helena and Ascension in the S Atlantic Ocean; São Tomé, Príncipe, Annobón, and Bioko in the Gulf of Guinea; the Cape Verde, Canary, and Madeira islands in the N Atlantic Ocean; and Mauritius, Réunion, Zanzibar, Pemba, and the Comoros and Seychelles in the Indian Ocean.

Geology and Geography

Most of Africa is a series of stable, ancient plateau surfaces, low in the north and west and higher (rising to more than 6,000 ft/1,830 m) in the south and east. The plateau is composed mainly of metamorphic rock that has been overlaid in places by sedimentary rock. The escarpment of the plateau is often in close proximity to the coast, thus leaving the continent with a generally narrow coastal plain; in addition, the escarpment forms barriers of falls and rapids in the lower courses of rivers that impede their use as transportation routes into the interior. Northern Africa is underlain by folded sedimentary rock and is, geologically, more closely related to Europe than to the rest of the continent of Africa; the Atlas Mts., which occupy most of the region, are a part of the Alpine mountain system of southern Europe. The entire African continent is surrounded by a narrow continental shelf. The lowest point on the continent is 509 ft (155 m) below sea level in Lake Assal in Djibouti; the highest point is Mt. Uhuru (Kibo; 19,340 ft/5,895 m), a peak of Kilimanjaro in NE Tanzania. From north to south the principal mountain ranges of Africa are the Atlas Mts. (rising to more than 13,000 ft/3,960 m), the Ethiopian Highlands (rising to more than 15,000 ft/4,570 m), the Ruwenzori Mts. (rising to more than 16,000 ft/4,880 m), and the Drakensberg Range (rising to more than 11,000 ft/3,350 m).

The continent's largest rivers are the Nile (the world's longest river), the Congo, the Niger, the Zambezi, the Orange, the Limpopo, and the Senegal. The largest lakes are Victoria (the world's second largest freshwater lake), Tanganyika, Albert, Turkana, and Nyasa (or Malawi), all in E Africa; shallow Lake Chad, the largest in W Africa, shrinks considerably during dry periods. The lakes and major rivers (most of which are navigable in stretches above the escarpment of the plateau) form an important inland transportation system.

Geologically, recent major earth disturbances have been confined to areas of NW and E Africa. Geologists have long noted the excellent fit (in shape and geology) between the coast of Africa at the Gulf of Guinea and the Brazilian coast of South America, and they have evidence that Africa formed the center of a large ancestral supercontinent known as Pangaea. Pangaea began to break apart in the Jurassic period to form Gondwanaland, which included Africa, the other southern continents, and India. South America was separated from Africa c.76 million years ago, when the floor of the S Atlantic Ocean was opened up by seafloor spreading; Madagascar was separated from it c.65 million years ago; and Arabia was separated from it c.20 million years ago, when the Red Sea was formed. There is also evidence of one-time connections between NW Africa and E North America, N Africa and Europe, Madagascar and India, and SE Africa and Antarctica.

Similar large-scale earth movements (see plate tectonics ) are also believed responsible for the formation of the Great Rift Valley of E Africa, which is the continent's most spectacular land feature. From c.40 to c.60 mi (60–100 km) wide, it extends in Africa c.1,800 mi (2,900 km), from the northern end of the Jordan Rift Valley in SW Asia to near the mouth of the Zambezi River; the eastern branch of the rift valley is occupied in sections by Lakes Nyasa and Turkana, and the western branch, curving N from Lake Nyasa, is occupied by Lakes Tanganyika, Kivu, Edward, and Albert. The lava flows of the recent and subrecent epochs in the Ethiopian Highlands, and volcanoes farther south, are associated with the rift; among the principal volcanoes are Kilimanjaro, Kenya, Elgon, Meru, and the Virunga range with Mt. Karisimbi, Nyiragongo, and Nyamuragira (Nyamulagira). A less spectacular rift, the Cameroon Rift, is associated with volcanic activity in W Africa and trends NE from St. Helena Island to São Tomé, Príncipe, and Bioko to near the Tibesti Massif in the Sahara.

Climate

Africa's climatic zones are largely controlled by the continent's location astride the equator and its almost symmetrical extensions into the Northern and Southern Hemispheres. Thus, except where altitude exerts a moderating influence on temperature or precipitation (permanently snowcapped peaks are found near the equator), Africa may be divided into six general climatic regions. Areas near the equator and on the windward shores of SE Madagascar have a tropical rain forest climate, with heavy rain and high temperatures throughout the year. North and south of the rain forest are belts of tropical savanna climate, with high temperatures all year and a seasonal distribution of rain during the summer season. The savanna grades poleward in both hemispheres into a region of semiarid steppe (with limited summer rain) and then into the arid conditions of the extensive Sahara (north) and the Kalahari (south). Belts of semiarid steppe with limited winter rain occur on the poleward sides of the desert regions. At the northern and southern extremities of the continent are narrow belts of Mediterranean-type climate with subtropical temperatures and a concentration of rainfall mostly in the autumn and winter months.

African Peoples

African peoples, who account for over 12% of the world's population, are distributed among 55 countries and are further distinguishable in terms of linguistic (see African languages ) and cultural groups, which number around 1,000. The Sahara forms a great ethnic divide. North of it, mostly Arabs predominate along the coast and Berbers (including the Tuareg) and Tibbu in the interior regions. Sub-Saharan Africa is occupied by a diverse variety of peoples including, among others, the Amhara, Mossi , Fulani , Yoruba , Igbo , Kongo (see Kongo, kingdom of ), Zulu (see Zululand ), Akan , Oromo , Masai , and Hausa . Europeans are concentrated in areas with subtropical climates or tropical climates modified by altitude; in the south are persons of Dutch and British descent, and in the northwest are persons of French, Italian, and Spanish descent. Lebanese make up an important minority community throughout W Africa, as do Indians in many coastal towns of S and E Africa. There are also significant Arab populations both in E Africa and more recently in W Africa. As a whole, Africa is sparsely populated; the highest densities are found in Nigeria, the Ethiopian highlands, the Nile valley, and around the Great Lakes (which include Victoria and Tanganyika). The principal cities of Africa are usually the national capitals and the major ports, and they usually contain a disproportionately large percentage of the national populations; Cairo, Lagos (Nigeria), Kinshasa (Democratic Republic of the Congo), Alexandria (Egypt), and Casablanca (Morocco) are the largest cities of Africa.

Economy

Most of Africa's population is rural, but, except for cash crops, such as cacao and peanuts, agricultural production is low by world standards; Africa produces three quarters of the world's cocoa beans and about one third of its peanuts. Rare and precious minerals (including much of the world's diamonds) are abundant in the continent's ancient crystalline rocks, which are found mostly to the south and east of a line from the Gulf of Guinea to the Sinai Peninsula; extensive oil, gas, and phosphate deposits occur in sedimentary rocks to the north and west of this general line. Manufacturing is concentrated in the Republic of South Africa and in N Africa (especially Egypt and Algeria). Despite Africa's enormous potential for hydroelectric power production, only a small percentage of it has been developed. Africa's fairly regular coastline affords few natural harbors, and the shallowness of coastal waters makes it difficult for large ships to approach the shore; deepwater ports, protected by breakwaters, have been built offshore to facilitate commerce and trade. Major fishing grounds are found over the wider sections of the continental shelf as off NW, SW, and S Africa and NW Madagascar.

Outline of History

Early History to 1500

Africa has the longest human history of any continent. African hominids date from at least 4 million years ago; agriculture, brought from SW Asia, appears to date from the 6th or 5th millennium BC Africa's first great civilization began in Egypt in 3400 BC; other ancient centers were Kush and Aksum. Phoenicians established Carthage in the 9th cent. BC and probably explored the northwestern coast as far as the Canary Islands by the 1st cent. BC Romans conquered Carthage in 146 BC and controlled N Africa until the 4th cent. AD Arabs began their conquest in the 7th cent. and, except in Ethiopia, Muslim traders extended the religion of Islam across N Africa and S across the Sahara into the great medieval kingdoms of the W Sudan. The earliest of these kingdoms, which drew their wealth and power from the control of a lucrative trans-Saharan trade in gold, salt, and slaves, was ancient Ghana, already thriving when first recorded by Arabs in the 8th cent. In the 13th cent. Ghana was conquered and incorporated into the kingdom of ancient Mali, famous for its gold and its wealthy capital of Timbuktu. In the late 15th cent. Mali was eclipsed by the Songhai empire and lost many provinces but remained an autonomous kingdom.

There are few written accounts of the southern half of the continent before 1500, but it appears from linguistic and archaeological evidence that the older inhabitants were gradually absorbed or displaced by agricultural, iron-working peoples speaking related Bantu languages who originated from near the modern Nigeria-Cameroon border. Between the 1st cent. BC and 1500, Bantu-speaking peoples became dominant over most of the continent S of the equator, establishing small farming villages and in places powerful kingdoms, such as Kongo, Luba, and Mwememutapa. Prior to and after 1500, pastoralists moved south until they encountered the various Bantu groups and founded the kingdom of Kitara in the 16th cent. They subsequently founded the kingdoms of Bunyoro, Buganda, Rwanda, and Ankole, all of which had elaborate social structures based on a cattle-owning aristocracy.

European Domination

The period of European domination of Africa began in the 15th cent. with Portuguese exploration of the coasts of Africa in an attempt to establish a safe route to India and to tap the lucrative gold trade of Sudan and the east coast trade in gold, slaves, and ivory conducted for centuries by Arabs and Swahili. In 1488 Bartolomeu Dias rounded the Cape of Good Hope; in 1498 Vasco da Gama reached the east coast and, the following year, India. In the centuries that followed, coastal trading stations were established by Portugal and later by the Dutch, English, French, and other European maritime powers; under them the slave trade rapidly expanded. At the same time Ottoman Turks extended their control over N Africa and the shores of the Red Sea, and the Omani Arabs established suzerainty over the east coast as far south as Cape Delgado.

Explorations in the 18th and 19th cent. reported the great natural wealth of the continent while capturing the imagination of Europeans, who viewed Africa as the "Dark Continent." These were key factors in the ensuing wave of European imperialism; between 1880 and 1912 all of Africa except Liberia and Ethiopia fell under control of European powers, with the boundaries of the new colonies often bearing no relationship to the realities of geography or to the political and social organization of the indigenous population. In the northwest and west, France ultimately acquired regions that came to be known as French West Africa, French Equatorial Africa, and the French Cameroons, and established protectorates in Algeria, Morocco, and Tunisia. Other French territories were French Somaliland, French Togoland, Madagascar, and Réunion. The main group of British possessions was in E and S Africa; it included the Anglo-Egyptian Sudan, British Somaliland, Uganda, Kenya, Tanganyika (after World War I), Zanzibar, Nyasaland, Northern and Southern Rhodesia, Bechuanaland, Basutoland, and Swaziland. Following Britain's victory in the South African War (1899–1902), its South African possessions (Transvaal, Orange Free State, Cape Colony, and Natal) became a dominion within the British Empire. Gambia, Sierra Leone, the Gold Coast, and Nigeria were British possessions on the west coast. Portugal's African empire was made up of Portuguese Guinea, Angola, and Mozambique, in addition to various enclaves and islands on the west coast. Belgium held the Belgian Congo and, after World War I, Ruanda-Urundi. The Spanish possessions in Africa were the smallest, being composed of Spanish Guinea, Spanish Sahara, Ifni, and the protectorate of Spanish Morocco. The extensive German holdings—Togoland, the Cameroons, German South-West Africa, and German East Africa—were lost after World War I and redistributed among the Allies; Italy's empire included Libya, Eritrea, and Italian Somaliland.

Movement toward Independence

The Union of South Africa was formed and became virtually self-governing in 1910, Egypt achieved a measure of sovereignty in 1922, and in 1925 Tangier, previously attached to Morocco, was made an international zone. At the end of World War II a rise in international trade spurred renewed exploitation of Africa's resources. France and Britain began campaigns to improve conditions in their African holdings, including access to education and investment in infrastructure. Africans were also able to pressure France and Britain into a degree of self-administration. Belgium and Portugal did little in the way of colonial development and sought greater control over their colonies during this period.

In the 1950s and 1960s, in the face of rising nationalism, most of the European powers granted independence to their territories. The sequence of change included independence for Libya in 1951; independence for Eritrea in federation with Ethiopia in 1952 (later absorbed by Ethiopia, Eritrea became fully independent in 1993); in 1956 independence for Morocco, Sudan, and Tunisia and the return of Tangier to Morocco; in 1957 independence for Ghana; in 1958 independence for Guinea and the return of Spanish Morocco to Morocco. In 1960 France granted independence to Cameroon, the Central African Republic, Chad, Congo (Brazzaville), Côte d'Ivoire, Dahomey (now Benin), Gabon, the Malagasy Republic (now Madagascar), Mali (briefly merged in 1959–60 with Senegal as the Sudanese Republic), Mauritania, Niger, Senegal, and Upper Volta (now Burkina Faso); also newly independent in 1960 were Congo (Kinshasa)—the former Belgian Congo—and Nigeria, Somalia, and Togo. In 1961 Sierra Leone and Tanganyika (now part of Tanzania) became independent, the Portuguese enclave of São João Baptista de Ajudá was seized by Dahomey, the British Cameroons were divided between Nigeria and Cameroon, and South Africa became a republic. In 1962 Algeria, Burundi, Rwanda, and Uganda became independent nations. Remaining British possessions after 1962 were Zanzibar, which gained independence in 1963 and joined with Tanganyika to form Tanzania in 1964; Gambia and Kenya, which became independent in 1963; Malawi (formerly Nyasaland) and Zambia (formerly Northern Rhodesia), independent in 1964; Botswana (formerly Bechuanaland) and Lesotho (formerly Basutoland), independent in 1966; and Mauritius and Swaziland, independent in 1968. In 1968 Spain granted independence to Equatorial Guinea, and in 1969 Spain returned Ifni to Morocco.

In 1974 Portuguese Guinea became independent as Guinea-Bissau, and the former Portuguese territories of Angola, Cape Verde, Mozambique, and São Tomé and Principe became independent in 1975. After Spain relinquished the Spanish Sahara (Western Sahara) to joint Moroccan-Mauritanian control in 1976, a guerrilla force undertook a struggle for independence there. Under rebel pressure, Mauritania yielded its sector of Western Sahara to Morocco in 1979; Morocco, for its part, built fortifications in the territory and resisted pressures for its independence. A cease-fire (1991) ended the fighting but did not lead to a final resolution. The Seychelles and the Comoros became independent in 1976 from Great Britain and France, respectively, and in 1977 the former French Territory of the Afars and the Issas became independent as Djibouti. When Rhodesia (formerly Southern Rhodesia) unilaterally declared itself independent in 1965, Great Britain termed the act illegal and imposed trade sanctions against the country; after a protracted civil war, however, Rhodesia gained recognized independence in 1980 as Zimbabwe. South West Africa, which had been administered by South Africa since 1922 under an old League of Nations mandate (South Africa's continued administration of the territory was declared illegal by the International Court of Justice in 1971), won its independence in 1990 as Namibia. Great Britain retains control of the islands of St. Helena and Ascension, and Mayotte and Réunion remain French. Spain retains the Canary Islands and Ceuta and Melilla, two small exclaves on Morocco's coast.

The Postcolonial Period

In the early postcolonial period the most pressing problems facing new African states were the need for aid to develop natural resources, provide education, and improve living standards; threats of secession and military coups; and shifting alliances among the states and with outside powers. Recognizing that unity and cooperation were needed, African nations established the Organization of African Unity (OAU) in 1963 in Addis Ababa. African nations were also forced to form alliances based on the cold war politics of the USSR, the United States, Cuba, and other countries in order to receive badly needed aid. This period saw the overthrow of democratic forms of government and numerous coups resulting in the installation of military regimes and single-party governments.

Beginning in the late 1960s and continuing through the mid-1970s, a severe drought desiccated the Sahel region S of the Sahara. The resulting famine, disease, and environmental destruction caused the death of thousands of people and forced the southward migration of additional hundreds of thousands to less affected areas.

From 1975 into the 21st cent., Africa continued to experience political, social, and economic upheaval. The postindependence era has also been marked by a rise in nationalist struggles. Wars in Sudan, Ethiopia, and Somalia continued, and political instability in these nations continued. Civil war in Ethiopia resulted in the birth (1993) of a new country, Eritrea; in 1998–2000 the two nations fought a bloody border war. Beginning in the 1970s, Chad fought Libyan expansionist activity with help of the French military. Relations between Chad and Libya were finally normalized in 1989. Chad remained beset, however, by regional and ethnic fighting, with rebels receiving support from Sudan in the early 21st cent. while Chad supported Sudanese rebels. The conflict between N and S Sudan largely ended with a peace agreement in 2005, and in 2011 South Sudan voted to become an independent nation. Other conflicts within Sudan, most notably in Darfur but also elsewhere, continued to fester.

In the late 1980s, there was a decline of Marxist influence in Angola, from where Cuban troops began to withdraw in 1989, as well as from civil war–torn Mozambique. A UN-aided peace process in Mozambique culminated in peaceful elections there in 1994, but civil conflict continued until 2002 in Angola, as numerous peace agreements between rebels and the government were broken.

South African blacks led an enduring struggle against white domination, with frequent confrontations (such as the Soweto uprising in 1976) leading to government repression and escalating violence. Throughout the 1980s the international community applied pressure in the form of economic sanctions in order to induce the South African government to negotiate with the African National Congress (ANC). In 1989 newly elected Prime Minister F. W. de Klerk promised democratic reforms that would phase out white minority rule, and in 1992 the legal underpinnings of apartheid were largely dismantled. Consequently, South Africa's black majority participated in the country's first fully democratic elections in 1994, which brought Nelson Mandela and the ANC to power.

Other African nations began to introduce democratic reforms in the late 1980s and early 1990s that included multiparty elections; transitions to democratically elected leadership have taken place in countries such as Mali, Zambia, Benin, and Malawi. Political instability and civil strife continued to plague several regions of the continent into the late 1990s, most notably Liberia and Sierra Leone in W Africa and Congo, Rwanda, and Burundi in the Great Lakes region. Peace treaties signed in Liberia (1997) and Sierra Leone (1999) between those countries' governments and insurgents promised some hope of stability.

In Rwanda in 1994 a Hutu-led government that provoked ethnic tensions leading to the genocide of nearly one million persons was overthrown by Tutsi-led forces; by 1997 there was a growing war between the Rwandan army and Hutu guerrilla bands. Also in 1997, 30 years of dictatorical rule in Zaïre were brought to an end, and the country's name was changed to the Democratic Republic of the Congo. The new government was soon threatened, however, by mutinous troops who assumed control of large areas of the country; a cease-fire was signed in 1999, but unrest continued in parts of Congo in subsequent years. Nigeria ushered in a new government in 1999 with the first democratically elected president since 1983. Several African countries made positive strides in managing market-oriented economic reform in the 1990s, most notably Ghana, Uganda, and Malawi.

In 1992–93, the worst African drought of the 20th cent. and numerous civil wars were the primary causes of a famine that spread across portions of sub-Saharan Africa and most severely affected the nations of Somalia and Mozambique. The scourge of AIDS has continued to pose a major health threat to many African nations, as a lack of economic resources often has prevented an effective response. Warfare, poverty, and hunger continue to present significant challenges in Africa, where ethnic tensions and political instability, along with the resulting economic disruption, still afflict many countries.

Mindful of the OAU's relative ineffectiveness in dealing with these issues and seeking an organization with greater powers to promote African economic, social, and political integration, African leaders established the African Union (AU), which superseded the OAU in 2002. The AU has proved somewhat more effective than OAU, but has had difficulty in successively confronting and resolving serious political crises (and sometimes civil war) in Somalia, Madagascar, Zimbabwe, and other nations.

Bibliography

See P. Curtin, Precolonial African History (1974); R. Hallet, Africa since 1875 (1974); W. A. Hance, The Geography of Modern Africa (rev. ed. 1975); J. D. Fage and R. Oliver, ed., The Cambridge History of Africa (8 vol., 1975–85); A. E. Afigb et al., The Making of Modern Africa (1986); UNESCO staff, The UNESCO General History of Africa (8 vol., 1988); T. Pakenham, The Scramble for Africa (1991); H. L. Wesseling, Divide and Rule: The Partition of Africa, 1880–1914 (1991, tr. 1996); R. Oliver, The African Experience (1992); J. Reader, Africa: A Biography of the Continent (1998); K. A. Appiah and H. L. Gates, Jr., ed., The Encyclopedia of the African and African American Experience (2000).

Africa

From the perspective of geologists and paleontologists, Africa takes center stage in the physical history and development of life on Earth. Africa is the world's second largest continent. Africa possesses the world's richest and most concentrated deposits of minerals such as gold, diamonds, uranium, chromium, cobalt, and platinum. It is also the cradle of human evolution and the birthplace of many animal and plant species, and has the earliest evidence of reptiles, dinosaurs, and mammals.

Present-day Africa, occupying one-fifth of Earth's land surface, is the central remnant of the ancient southern super-continent called Gondwanaland, a landmass once made up of South America , Australia , Antarctica , India, and Africa. This massive supercontinent broke apart between 195 million and 135 million years ago, cleaved by the same geological forces that continue to transform Earth's crust today.

Plate tectonics are responsible for the rise of mountain ranges, the gradual drift of continents, earthquakes, and volcanic eruptions . The fracturing of Gondwanaland took place during the Jurassic Period , the middle segment of the Mesozoic Era when dinosaurs flourished on Earth. It was during the Jurassic that flowers made their first appearance, and dinosaurs like the carnivorous Allosaurus and plant eating Stegasaurus lived.

Geologically, Africa is 3.8 billion years old, which means that in its present form or joined with other continents as it was in the past, Africa has existed for four-fifths of Earth's 4.6 billion years. Africa's age and geological continuity are unique among continents. Structurally, Africa is composed of five cratons (structurally stable, undeformed regions of Earth's crust). These cratons, in south, central, and west Africa are mostly igneous granite , gneiss , and basalt , and formed separately between 3.6 and 2 billion years ago, during the Precambrian Era.

The Precambrian, an era which comprises more than 85% of the planet's history, was when life first evolved and the earth's atmosphere and continents developed. Geochemical analysis of undisturbed African rocks dating back 2 billion years has enabled paleoclimatologists to determine that Earth's atmosphere contained much higher levels of oxygen than today.

Africa, like other continents, "floats" on a plastic layer of Earth's upper mantle called the asthenosphere . The overlying rigid crust or lithosphere can be as thick as 150 mi (240 km) or under 10 mi (16 km), depending on location. The continent of Africa sits on the African plate, a section of the earth's crust bounded by mid-oceanic ridges in the Atlantic and Indian Oceans . The entire plate is creeping slowly toward the northwest at a rate of about 0.75 in (2 cm) per year.

The African plate is also spreading or moving outward in all directions, and therefore Africa is growing in size. Geologists state that sometime in the next 50 million years, East Africa will split off from the rest of the continent along the East African rift which stretches 4,000 mi (6,400 km) from the Red Sea in the north to Mozambique in the south.

Considering its vast size, Africa has few extensive mountain ranges and fewer high peaks than any other continent. The major ranges are the Atlas Mountains along the northwest coast and the Cape ranges in South Africa. Lowland plains are also less common than on other continents.

Geologists characterize Africa's topography as an assemblage of swells and basins. Swells are rock strata warped upward by heat and pressure, while basins are masses of lower lying crustal surfaces between swells. The swells are highest in East and central West Africa where they are capped by volcanic flows originating from the seismically active East African rift system. The continent can be visualized as an uneven tilted plateau, one that slants down toward the north and east from higher elevations in the west and south.

During much of the Cretaceous Period , from 130 million to 65 million years ago, when dinosaurs like tyrannosaurus, brontosaurus, and triceratops walked the earth, Africa's coastal areas and most of the Sahara Desert were submerged underwater. Global warming during the Cretaceous Period melted polar ice and caused ocean levels to rise. Oceanic organic sediments from this period were transformed into the petroleum and natural gas deposits now exploited by Libya, Algeria, Nigeria, and Gabon. Today, oil and natural gas drilling is conducted both on land and offshore on the continental shelf .

The continent's considerable geological age has allowed more than enough time for widespread and repeated erosion , yielding soils leached of organic nutrients but rich in iron and aluminum oxides. Such soils are high in mineral deposits such as bauxite (aluminum ore), manganese, iron, and gold, but they are very poor for agriculture. Nutrient-poor soil , along with deforestation and desertification (expansion of deserts) are just some of the daunting challenges facing African agriculture in modern times.

The most distinctive and dramatic geological feature in Africa is undoubtedly the East African rift system. The rift opened up in the Tertiary Period , approximately 65 million years ago, shortly after the dinosaurs became extinct. The same tectonic forces that formed the rift valley and which threaten to eventually split East Africa from the rest of the continent have caused the northeast drifting of the Arabian plate, the opening of the Red Sea to the Indian Ocean, and the volcanic uplifting of Africa's highest peaks including its highest, Kilimanjaro in Tanzania. Mount Kibo, the higher of Kilimanjaro's two peaks, soars 19,320 ft (5,796 m) and is permanently snowcapped despite its location near the equator.

Both Kilimanjaro and Africa's second highest peak, Mount Kenya (17,058 ft; 5,117 m) sitting astride the equator, are actually composite volcanos, part of the vast volcanic field associated with the East African rift valley. The rift valley is also punctuated by a string of lakes , the deepest being Lake Tanganyika with a maximum depth of 4,708 ft (1,412 m). Only Lake Baikal in Eastern Russia is deeper at 5,712 ft (1,714 m).

Seismically, the rift valley is very much alive. Lava flows and volcanic eruptions occur about once a decade in the Virunga Mountains north of Lake Kivu along the western stretch of the rift valley. One volcano in the Virunga area in eastern Zaire which borders Rwanda and Uganda actually dammed a portion of the valley formerly drained by a tributary of the Nile River, forming Lake Kivu as a result.

On its northern reach, the 4,000-mi (6,400-km) long rift valley separates Africa from Asia . The rift's eastern arm can be traced from the Gulf of Aqaba separating Arabia from the Sinai Peninsula, down along the Red Sea, which divides Africa from Arabia. The East African rift's grabens (basins of crust bounded by fault lines) stretch through the extensive highlands of central Ethiopia which range up to 15,000 ft (4,500 m) and then along the Awash River. Proceeding south, the rift valley is dotted by a series of small lakes from Lake Azai to Lake Abaya and then into Kenya by way of Lake Turkana.

Slicing through Kenya, the rift's grabens are studded by another series of small lakes from Lake Baringo to Lake Magadi. The valley's trough or basin is disguised by layers of volcanic ash and other sediments as it threads through Tanzania via Lake Natron. However, the rift can be clearly discerned again in the elongated shape of Lake Malawi and the Shire River Valley, where it finally terminates along the lower Zambezi River and the Indian Ocean near Beira in Mozambique.

The rift valley also has a western arm which begins north of Lake Mobutu along the Zaire-Uganda border and continues to Lake Edward. It then curves south along Zaire's eastern borders forming that country's boundaries with Burundi as it passes through Lake Kivu and Tanzania by way of Lake Tanganyika.

The rift's western arm then extends toward Lake Nysasa (Lake Malawi). Shallow but vast, Lake Victoria sits in a trough between the rift's two arms. Although the surface altitude of the rift valley lakes like Nyasa and Tanganyika are hundreds of feet above sea level, their floors are hundreds of feet below due to their great depths.

The eastern arm of the rift valley is much more active than the western branch, volcanically and seismically. There are more volcanic eruptions in the crust of the eastern arm with intrusions of magma (subterranean molten rock) in the middle and lower crustal depths. Geologists consider the geological forces driving the eastern arm to be those associated with the origin of the entire rift valley and deem the eastern arm to be the older of the two.

It was in the great African rift valley that hominids, or human ancestors, arose. Hominid fossils of the genus Australopithicus dating 3–4 million years ago have been unearthed in Ethiopia and Tanzania. And the remains of a more direct ancestor of man, Homo erectus, who was using fire 500,000 years ago, have been found in Olduvai Gorge in Tanzania as well as in Morocco, Algeria, and Chad.

Paleontologists, who study fossil remains, employ radioisotope dating techniques to determine the age of hominid and other species' fossil remains. This technique measures the decay of short-lived radioactive isotopes like carbon and argon to determine a fossil's age. This is based on the radioscope's atomic half-life , or the time required for half of a sample of a radioisotope to undergo radioactive decay. Dating is typically done on volcanic ash layers and charred wood associated with hominid fossils rather than the fossils themselves, which usually do not contain significant amounts of radioactive isotopes.

Present-day volcanic activity in Africa is centered in and around the East African rift valley. Volcanoes are found in Tanzania at Oldoinyo Lengai and in the Virunga range on the Zaire-Uganda border at Nyamlagira and Nyiragongo. There is also volcanism in West Africa. Mount Cameroon (13,350 ft; 4,005 m) along with smaller volcanos in its vicinity, stand on the bend of Africa's West Coast in the Gulf of Guinea, and are the exception. They are the only active volcanoes on the African mainland not in the rift valley.

However, extinct volcanoes and evidence of their activity are widespread on the continent. The Ahaggar Mountains in the central Sahara contain more than 300 volcanic necks that rise above their surroundings in vertical columns of 1,000 ft or more. Also, in the central Sahara, several hundred miles to the east in the Tibesti Mountains, there exist huge volcanic craters or calderas. The Trou au Natron is 5 mi (8 km) wide and over 3,000 ft (900 m) deep. In the rift valley, the Ngorongoro Crater in Tanzania, surrounded by teeming wildlife and spectacular scenery, is a popular tourist attraction. Volcanism formed the diamonds found in South Africa and Zaire. The Kimberly diamond mine in South Africa is actually an ancient volcanic neck.

The only folded mountains in Africa are found at the northern and southern reaches of the continent. Folded mountains result from the deformation and uplift of the earth's crust, followed by deep erosion. Over millions of years this process built ranges like the Atlas Mountains, which stretch from Morocco to Algeria and Tunisia.

Geologically, the Atlas Mountains are the southern tangent of the European Alps, geographically separated by the Strait of Gibraltar in the west and the Strait of Sicily in the east. The Atlas are strung across northwest Africa in three parallel arrays; the coastal, central, and Saharan ranges. By trapping moisture, the Atlas Mountains carve out an oasis along a strip of northwest Africa compared with the dry and inhospitable Sahara Desert just to the south.

The Atlas Mountains are relatively complex folded mountains featuring horizontal thrust faults and ancient crystalline cores. On the other hand, the Cape ranges are older, simpler structures, analogous in age and erosion to the Appalachian Mountains of the eastern United States. The Cape ranges rise in a series of steps from the ocean to the interior, flattening out in plateaus and rising again to the next ripple of mountains.

For a continent of its size, Africa has very few islands lying off its coast. The major Mediterranean islands of Corsica, Sardinia, Sicily, Crete, and Cyprus owe their origins to the events that formed Europe's Alps, and are a part of the Eurasian plate, not Africa. Islands lying off Africa's Atlantic Coast like the Canaries, Azores, and even the Cape Verde Islands near North Africa are considered Atlantic structures. Two islands in the middle of the South Atlantic, Ascension and St. Helena, also belong to the Atlantic. Islands belonging to Equatorial Guinea as well as the island country of Sao Tome and Principe at the sharp bend of Africa off of Cameroon and Gabon are related to volcanic peaks of the Cameroon Mountains, the principal one being Mount Cameroon.

Madagascar, the world's fourth largest island after Greenland, New Guinea, and Borneo, is a geological part of ancient Gondwanaland. The island's eastern two-thirds are composed of crystalline igneous rocks , while the western third is largely sedimentary. Although volcanism is now quiescent on the island, vast lava flows indicate widespread past volcanic activity. Madagascar's unique plant and animal species testify to the island's long separation from the mainland.

Marine fossils, notably tribolites dating from the Cambrian Period (505–570 million years ago; the first period of the Paleozoic Era ) have been found in southern Morocco and Mauritania. Rocks from the succeeding period, the Ordovician (500–425 million years ago) consist of sandstones with a variety of fossilized marine organisms; these rocks occur throughout northern and western Africa, including the Sahara.

The Ordovician Period was characterized by the development of brachiopods (shellfish similar to clams), corals, starfish, and some organisms that have no modern counterparts, called sea scorpions, conodonts, and graptolites. At the same time, the African crust was extensively deformed. The continental table of the central and western Sahara was lifted up almost a mile (1.6 km). The uplifting alternated with crustal subsidings, forming valleys that were periodically flooded.

During the Ordovician Period , Africa, then part of Gondwanaland, was situated in the southern hemisphere on or near the South Pole. It was toward the end of this period that huge glaciers formed across the present-day Sahara and the valleys were filled by sandstone and glacial deposits. Although Africa today sits astride the tropics, it was once the theater of the Earth's most spectacular glacial activity. In the next period, the Silurian (425–395 million years ago), further marine sediments were deposited.

The Silurian was followed by the Devonian, Mississippian, and Pennsylvanian Periods (408–286 million years ago), the time interval when insects, reptiles, amphibians, and forests first appeared. A continental collision between Africa (Gondwanaland) and the North American plate formed a super-supercontinent (Pangaea) and raised the ancient Mauritanide mountain chain that once stretched from Morocco to Senegal. During the late Pennsylvanian Period , layer upon layer of fossilized plants were deposited, forming seams of coal in Morocco and Algeria.

When Pangaea and later Gondwanaland split apart in the Cretaceous Period (144–66 million years ago), a shallow sea covered much of the northern Sahara and Egypt as far south as the Sudan. Arabia, subjected to many of the same geological and climatic influences as northern Africa, was thrust northward by tectonic movements at the end of the Oligocene and beginning of the Miocene Epochs (around 30 million years ago). During the Oligocene and Miocene (5–35 million years ago; segments of the modern Cenozoic Era ) bears, monkeys, deer, pigs, dolphins, and early apes first appeared.

Arabia at this time nearly broke away from Africa. The Mediterranean swept into the resulting rift, forming a gulf that was plugged by an isthmus at present-day Aden on the Arabian Peninsula and Djibouti near Ethiopia. This gulf had the exact opposite configuration of today's Red Sea, which is filled by waters of the Indian Ocean.

As the Miocene Epoch ended about five million years ago, the isthmus of Suez was formed and the gulf (today's Red Sea) became a saline (salty) lake. During the Pliocene (1.6–5 million years ago) the Djibouti-Aden isthmus subsided, permitting the Indian Ocean to flow into the rift that is now the Red Sea.

In the Pleistocene Epoch (11,000–1.6 million years ago), the Sahara was subjected to humid and then to dry and arid phases, spreading the Sahara desert into adjacent forests and green areas. About 5,000–6,000 years ago in the post glacial period of the modern epoch, the Holocene, a further succession of dry and humid stages, further promoted desertification in the Sahara as well as the Kalahari in southern Africa.

Earth scientists state the expansion of the Sahara is still very much in evidence today, causing the desertification of farm and grazing land and presenting the omnipresent specter of famine in the Sahel (Saharan) region.

Africa has the world's richest concentration of minerals and gems. In South Africa, the Bushveld Complex, one of the largest masses of igneous rock on Earth, contains major deposits of strategic metals such as platinum, chromium, and vanadium—metals that are indispensable in tool making and high tech industrial processes. The Bushveld complex is about 2 billion years old.

Another spectacular intrusion of magmatic rocks composed of olivine , augite, and hypersthene occurred in the Archean Eon over 2.5 billion years ago in Zimbabwe. Called the Great Dyke, it contains substantial deposits of chromium, asbestos, and nickel. Almost all of the world's chromium reserves are found in Africa. Chromium is used to harden alloys, to produce stainless steels, as an industrial catalyst, and to provide corrosion resistance.

Unique eruptions that occurred during the Cretaceous in southern and central Africa formed kimberlite pipes—vertical, near-cylindrical rock bodies caused by deep melting in the upper mantle. Kimberlite pipes are the main source of gem and industrial diamonds in Africa. Africa contains 40% of the world's diamond reserves, which occur in South Africa, Botswana, Namibia, Angola, and Zaire.

In South Africa, uranium is found side-by-side with gold, thus decreasing costs of production. Uranium deposits are also found in Niger, Gabon, Zaire, and Namibia. South Africa alone contains half the world's gold reserves. Mineral deposits of gold also occur in Zimbabwe, Zaire, and Ghana. Alluvial gold (eroded from soils and rock strata by rivers ) can be found in Burundi, Côte d'Ivoire, and Gabon.

As for other minerals, half of the world's cobalt is in Zaire and a continuation into Zimbabwe of Zairian cobalt-bearing geological formations gives the former country sizable reserves of cobalt as well. One quarter of the world's aluminum ore is found in a coastal belt of West Africa stretching 1,200 mi (1,920 km) from Guinea to Togo, with the largest reserves in Guinea.

Major coal deposits exist in southern Africa, North Africa, Zaire, and Nigeria. North Africa is awash in petroleum reserves, particularly in Libya, Algeria, Egypt, and Tunisia. Nigeria is the biggest petroleum producer in West Africa, but Cameroon, Gabon, and the Congo also contain oil reserves. There are also petroleum reserves in southern Africa, chiefly in Angola.

Most of Africa's iron reserves are in western Africa, with the most significant deposits in and around Liberia, Guinea, Gabon, Nigeria, and Mauritania. In West Africa as well as in South Africa where iron deposits are also found, the ore is bound up in Precambrian rock strata.

Africa, like other continents, has been subjected to gyrating swings in climate during the Quartenary Period of the last 2 million years. These climatic changes have had dramatic affects on landforms and vegetation. Some of these cyclical changes may have been driven by cosmic or astronomical phenomena including asteroid and comet collisions.

But the impact of humankind upon the African environment has been radical and undeniable. Beginning 2,000 years ago and accelerating to the present day, African woodland belts have been deforested. Such environmental degradation has been exacerbated by overgrazing, agricultural abuse, and man-made changes, including possible global warming partially caused by the buildup of man-made carbon dioxide , chlorofluorocarbons (CFCs), and other greenhouse gases .

Deforestation, desertification, and soil erosion pose threats to Africa's man-made lakes and thereby Africa's hydroelectric capacity. Africa's multiplying and undernourished populations exert ever greater demands on irrigated agriculture, but the continent's water resources are increasingly taxed beyond their limits. To stabilize Africa's ecology and safeguard its resources and mineral wealth, many earth scientists argue that greater use must be made of sustainable agricultural and pastoral practices. Progress in environmental and resource management, as well as population control is also vital.

See also Earth (planet)

AFRICA

Portuguese colonial and trading ventures in Africa, whose beginning is conventionally dated from the conquest of Ceuta in 1415, continued with the gradual exploration of the Saharan and then West African Atlantic coastline from the mid-1430s to the mid-1480s. Having reached an early peak in the first three decades of the sixteenth century, the colonial enterprise stalled for the time being, as a result of defeats in Morocco and settlement setbacks in West Africa and Angola. The latter were partially offset, however, by the prosperity of the Cape Verde Islands and of São Tomé Island, as well as by commercial breakthroughs in West and East Africa. Subsequent economic stagnation, foreign competition, and the Dutch assaults and occupation of 1620–1648 helped to erode Portugal's African interests. New vigorous expansion followed, however, above all in Angola and Mozambique, from 1650 onward. Portuguese adventurers, entrepreneurs, and chartered companies maintained an important role in the trans-Atlantic slave trade and in Indian Ocean commerce throughout the eighteenth century, and swings in the prosperity of Brazil and in the attendant demand for slaves visibly shaped the economic fortunes of the African colonies.

MOROCCO

Between 1415 and 1521, Portugal occupied six Moroccan coastal towns (Ceuta, 1415; Ksar as-Saghir, 1458; Arzilla and Tangier, 1471; Safi and Azemmur, 1507–1513), and built six new strategic forts along Morocco's Atlantic shore. Failing to tap into the trans-Saharan caravan trade, the outposts remained largely isolated, and maintaining them quickly became a serious burden. Following an era of neglect in the 1520s and 1530s, the outposts were repaired and new fortifications built by the early 1540s (particularly at Mazagan). A spirit of retrenchment nonetheless prevailed, and heavy losses between 1541 and 1550 reduced the Portuguese holdings to Ceuta, Tangier, and Mazagan. When Portugal reclaimed its independence from Spain in 1640, Ceuta pledged allegiance to Spain; Catherine of Bragança's marriage to Charles II gave Tangier to England in 1661; and Mazagan (modern El Jadida), a textbook early modern fortress town, surrendered to Morocco in 1769.

CAPE VERDE AND WEST AFRICA

Discovered around 1460, three of the Cape Verde Islands (Santiago, Fogo, and Maio) were quickly colonized and developed an economy buttressed by trade in slaves, cattle, salt, and dyestuffs. On the African mainland, a small fort was built at Arguim (Mauritania; c. 1450), but the key Portuguese footholds were the fort of São Jorge da Mina (Ghana; 1482), nearby Axim (1490s), and another outpost near Cabo das Redes (1500). A short-lived trading post was maintained at Ughoton (Benin) (1487–1507). An important seasonal station sprang up at the site of the native merchant fairs held at Kantor, on the upper Gambia River. Elsewhere, in Senegal, in Gambia, in the "Guinea Rivers" region, and farther on to Sierra Leone, Liberia, and Ivory Coast, as well as in the Bight of Benin, the Portuguese traded intermittently, often from shipboard. African gold, slaves, ivory, civet, wax, and spices—malaguetta (also known as "grains of paradise," the subtly pungent seeds of the West African plant Aframomum melegueta, belonging to the ginger family [Zingiberaceae]) and tailed pepper (the slightly bitter pungent seeds of so-called false cubeb pepper [Piper guinense or Piper clusii ])—were exchanged for horses, European cloth, North African fabrics, Indian cottons, salt, hats, iron, brass, copper, and tin articles, beads, and cowrie shells.

Mismanagement, foreign interlopers (Spanish, French, English, and then the Dutch), policy failures, and African politics eroded trade profits after 1525. By the 1530s Arguim was in decline, and Mina's gold exports tapered off after 1550. Military penetration into the hinterland of Mina failed, as did projects to establish a full-scale colony in the 1570s and 1590s. Cape Verde experienced some prosperity, but viable local export production was limited to horses, the violet dyestuff orchil (obtained from local lichens), salt, maize, and cotton. In the 1600s, mainland trading posts between Mauritania and Sierra Leone came to depend more heavily on Cape Verde, and the Portuguese asserted themselves between the Casamance and Geba rivers. The Mina gold trade recovered in the early 1600s, but after 1618–1619 its decline was precipitous. In 1620–1641, the Portuguese forts in West Africa fell to the Dutch, Mina capitulating in 1637 and Arguim in 1638. The losses were never recovered.

In 1680–1706, trade between Cape Verde and the African mainland was controlled by the Company of Cape Verde and Cachéu, a privileged exporter of slaves to Spanish America. The English, however, established a stake in the island trade after 1706. From 1757 to 1786, chartered companies, notably the Company of Grão-Pará and Maranhão, once again dominated Cape Verde and the Guinea coast. Reforms brought the demise of the last donatory privileges and the creation of a new Captaincy General of Cape Verde. The authority of the captains, however, was curtailed by the power of the companies, and new trading stations replaced only partially those lost by 1641. The most conspicuous addition was the fort of São João Baptista de Ajudá (1677–1680) in Dahomey, which became a hub of the slave and ivory trade. Subordinate to the Captaincy of São Tomé, Ajudá was controlled by the Company of Cape Verde and Cachéu until 1706. Subsequently, exports of slaves to Brazil secured maintenance subsidies from Bahia for the Ajudá fort.

SAÕ TOMÉ AND PRÍNCIPE

Following the discovery of the islands of São Tomé, Ano Bom, and Príncipe (originally Santo Antão) in 1470–1471, effective settlement was undertaken in 1486–1510. The already inhabited island of Fernão do Pó, by contrast, resisted colonization. São Tomé, populated by Portuguese, free Africans, and baptized Jews sent out by the crown, quickly became a slaveholding society geared toward sugar production and the reexport of African slaves. By 1529, there were some sixty sugar mills on the island, but the heyday of sugar production was over by 1600, and internal unrest, Brazilian competition, sugarcane blight, and the emigration of planters to Brazil reduced São Tomé to dire straits by 1615. The island's role as a transit point for slaves also declined, and Dutch raids (from 1612 onward) culminated in the occupation of the island's strategic port in 1641–1644. Although sugar continued to be produced and the cultivation of ginger was attempted, by the 1670s São Tomé was only a modest hub of regional trade. Administrative reforms in 1753–1770 helped to improve conditions, but maintaining Portuguese control over all four islands was a burden. The treaties of San Ildefonso and El Pardo (1777–1778) ceded Fernão do Pó (now Fernando Póo) and Ano Bom (now Annobón) to Spain.

ANGOLA

Following a haphazard expansion of trade in the 1540s–1560s, a doação, 'crown donation', of land south of the Kwanza River was made in 1571 to Paulo Dias de Novais. The first settlement was organized in Luanda Bay in 1575, and the colony quickly became involved in slaving (exporting c. 10,000 slaves in the 1570s). The failure to extract concessions from the kingdom of Ndongo led to a series of wars (1579–1590), which the colonists at first fought in alliance with King António I of Kongo. Demographic losses to disease and warfare were severe, however, and by 1590 exhaustion and defeats stalled the inland expansion. The crown assumed direct control of the colony.

In the 1600s, commerce replaced raids and warfare as a source of captives in the Luanda hinterland. As Portuguese military influence revived, permanent slave market networks stretched eastward (to the Kwango and the middle Kwanza rivers) and, in 1617, fresh conquests were launched from the new coastal outpost of Benguela in central Angola. Raids yielded cattle, sheep, and cheaper slaves than those exported through Luanda. The Dutch occupation of Luanda (1641–1648) partly isolated the colony from the remaining Portuguese Atlantic networks, but slaving continued, based on the (Portuguese) loyalist refuge of Massangano. The liberation of Luanda by the Brazilian fleet of Salvador Correia de Sá reaffirmed the ties between Angola and its main outlet for slaves, Brazil.

Thrusting from Benguela into central Angola's highlands, dominated by the recently formed Ovimbundu kingdoms of Imbangala warlords, the Portuguese reached the upper Katumbela River by the 1650s, and the Kunene River by c. 1720. Here too, raiding gradually yielded to organized trade in slaves, and in the 1770s many of the Ovimbundu warlords were replaced with merchant rulers. In the north, campaigns were fought in 1744 against the kingdom of Matamba. The liberalization of trade in 1755–1758 could not halt a relative decline during the Brazilian depression of the 1760s–1770s, and attempts to stimulate settlement, agriculture, and manufacturing failed. The revival of Brazilian plantations in the 1780s and 1790s, however, brought the trade in slaves to a new high, and fresh sources of slaves were tapped by Portuguese, Luso-African, and Ovimbundu traders as far east as the sources of the Zambezi River.

MOZAMBIQUE

Initial cautious contacts with the Muslim seaside towns of Sofala (Mozambique), Mozambique, and Malindi (Kenya), were followed in 1505 by conquest, in spite of the hostility of Mombasa (Kenya) and Kilwa (Tanzania). The Portuguese then penetrated up the Zambezi River, establishing a trading post at Sena in 1531, and reaching Tete shortly thereafter. The magnet that drew them was the gold and imaginary silver of the Karanga empire of Mwene Matapa (south of the middle and upper Zambezi River) and of its southern outliers (Manica and Butua), as well as the ivory traded in these areas and in the Malawian realm of Kalonga. The military expeditions up the Zambezi and into Manica in the 1570s secured only mixed results, but by then tiny, yet tenacious, groups of Portuguese, Luso-African, and East Indian merchants had already scattered inland. Commerce shifted from Arab networks to Portuguese-dominated ones, with Portuguese India as the focal point and Goa as the administrative pivot.

At first hampered by ill-suited policies, the crown trade failed to prosper. Subsequently, corruption, smuggling, and lack of control over private traders made the Portuguese crown oscillate between direct administration and farming out all commerce to the entrepreneur Captains of Mozambique. Monopoly companies asserted themselves later on. By the 1650s, the inability of Mwene Matapa and Malawi to control dissident regions enticed Portuguese and other adventurers to become overlords or local protectors of large territories (prazos). At the same time, however, Arab resurgence in the north led to the loss of Mombasa and its dependencies, Pate (Kenya) and Zanzibar (lost in 1698, and then briefly recaptured and definitively lost in 1728–1729).

The heyday of the large prazos was over by c. 1730. Internecine warfare, the twists of African politics, and low production levels spelled their doom. Trade, tribute, and surface mining of gold, iron, and copper were by far the most lucrative activities. Despite state inducements and liberal reforms in 1755–1761, the much smaller, successor prazo estates of 1750–1800 never became effective producers of cash crops. The growth of the trade in slaves during the last decades of the eighteenth century, fueled by economic pressures, resurgent Brazilian demand, and the famines of 1792–1796 led to abuses that undermined the legitimacy and political stability of the prazos, initiating their decline.

See also Slavery and the Slave Trade .

BIBLIOGRAPHY

Birmingham, David. Central Africa to 1870: Zambezia, Zaire and the South Atlantic. Cambridge, U.K., 1981.

Cook, Weston F. The Hundred Years War for Morocco: Gunpowder and the Military Revolution in the Early Modern Muslim World. Boulder, Colo., 1994.

Garfield, Robert. A History of São Tomé Island, 1470–1655: The Key to Guinea. San Francisco, 1992.

Isaacman, Allen F. Mozambique: The Africanization of a European Institution: The Zambezi Prazos, 1750–1902. Madison, Wis., 1972.

Newitt, Malyn. A History of Mozambique. London, 1995.

Parreira, Adriano T. The Kingdom of Angola and Iberian Interference, 1483–1643. Uppsala, 1985.

Vogt, John. Portuguese Rule on the Gold Coast, 1469–1682. Athens, Ga., 1979.

Martin Malcolm Elbl

Africa

Africa is the world's second largest continent, encompassing an area of 11,677,240 square miles (30,244,051 square kilometers), including offshore islands. Recognized as the birthplace of the human race and of many other animal and plant species, it also possesses the world's richest and most concentrated deposits of minerals such as gold, diamonds, uranium, chromium, cobalt, and platinum.

Origin of Africa

Geologically, Africa is 3.8 billion years old (Earth is 4.6 billion years old). Present-day Africa, occupying one-fifth of Earth's land surface, is the central remnant of the ancient southern supercontinent called Gondwanaland, a landmass once made up of South America, Australia, Antarctica, India, and Africa. This massive supercontinent broke apart between 195 million and 135 million years ago, split by the same geological forces—continental drifting, earthquakes, volcanos—that continue to transform Earth's crust today.

General features

Africa has fewer high peaks than any other continent and few extensive mountain ranges. The major ranges are the Atlas Mountains along the northwest coast and the Drakensberg Mountains in South Africa. The highest point on the continent is Kibo (19,340 feet/5,895 meters), a peak of Mount Kilimanjaro in northeast Tanzania. Despite its location near the equator, the peak is permanently snowcapped.

Geologists characterize Africa's topography (physical features) as a collection of swells and basins. Swells are layers of rock warped upward by Earth's internal heat and pressure. Basins are broad, lower-lying areas between swells. The continent can be visualized as an uneven tilted plateau, one that slants down toward the north and east. The swells are highest in East and central West Africa, where they are capped by volcanic flows originating from the Great Rift Valley.

Great Rift Valley

The most distinctive and dramatic geological feature in Africa is the Great Rift Valley. The rift opened up approximately 65 million years ago, shortly after the dinosaurs became extinct. It extends almost 3,000 miles (4,830 kilometers) from northern Syria down the eastern side of the African continent to central Mozambique. The ranges in elevation of the valley are great, from about 1,300 feet (395 meters) below sea level at the Dead Sea to over 6,000 feet (1,830 meters) above sea level in southern Kenya.

The Great Rift Valley has a western branch that begins north of Lake Albert (Lake Mobutu) along the Zaire-Uganda border. It then curves south along Zaire's eastern border, forming that country's boundary with Burundi. This branch is punctuated by a string of lakes, the deepest being Lake Tanganyika (on the boundary between Tanzania and Zaire), with a maximum depth of 4,710 feet (1,436 meters).

The rift valley is alive seismically, with much earthquake-related activity occurring. About once a decade lava flows and volcanic eruptions take place in the Virunga mountain range on the Zaire-Uganda border. The main or eastern branch of the rift valley experiences more volcanic and seismic activity than the western branch. Geologists consider the geological forces driving the main branch to be those associated with the origin of the entire rift valley and deem the main branch to be the older of the two.

Human evolution

Hominids, or human ancestors, arose in the Great Rift Valley. Paleontologists, scientists who study fossil remains, have unearthed in Ethiopia and Tanzania hominid fossils that have been dated from three to four million years old. Hominid remains have also been found in Morocco, Algeria, and Chad.

Volcanic activity outside the Great Rift Valley

Mount Cameroon, which stands 13,350 feet (4,005 meters), and a few smaller neighboring volcanos in Cameroon on the Gulf of Guinea are the only active volcanos on the African mainland outside of the Great Rift Valley. However, extinct volcanos and evidence of their activity are widespread on the continent. The Ahaggar Mountains in the central Sahara Desert contain more than 300 volcanic necks, massive vertical columns of volcanic rock, that rise 1,000 feet (305 meters) or more. Also in the central Sahara, several hundred miles to the east in the Tibesti Mountains, there exist huge volcanic craters or calderas. In the Great Rift Valley, the Ngorongoro Crater in Tanzania, surrounded by teeming wildlife and spectacular scenery, is a popular tourist attraction. Volcanism formed the diamonds found in South Africa and Zaire. The Kimberly diamond mine in South Africa is actually an ancient volcanic neck.

Origin of Sahara Desert

Between 1,600,000 and 11,000 years ago, the Sahara was subjected to humid and then to arid (dry) phases, causing it to spread into adjacent forests and green areas. About 5,000 to 6,000 years ago, further humid and arid phases promoted desertification (the transformation of arid or semiarid land into desert) in the Sahara as well as the Kalahari in southern Africa. Earth scientists say the expansion of the Sahara is still occurring today, with the desertification of farm and grazing land responsible for the spread of famine in the Sahel or Saharan region.

Words to Know

Basins: Broad, lower-lying areas between swells.

Deforestation: Total clearing of trees and other plants from forest areas.

Desertification: Transformation of arid or semiarid productive land into desert.

Gondwanaland: Ancient supercontinent that was made up of present-day Africa, South America, Australia, Antarctica, and India.

Swells: Layers of rock warped upward by Earth's internal heat and pressure.

Volcanic neck: A massive vertical column of volcanic rock, formed in the vent of a volcano, that has been exposed by erosion of the flanks of the volcano.

Minerals and resources

Africa holds the world's richest concentration of minerals and gems. In South Africa, the two-billion-year-old Bushveld Complex, one of Earth's largest masses of igneous rock (cooled and hardened molten rock), contains major deposits of metals such as platinum, chromium, and vanadium. These metals are indispensable in toolmaking and high-tech industrial processes. Almost all of the world's chromium reserves are found in Africa. Chromium is used to harden alloys (metal mixtures), to produce stainless steels, and to provide resistance to corrosion.

As for other minerals, one-half of the world's cobalt is in Zaire. Onequarter of the world's aluminum ore is found in a coastal belt of West Africa stretching 1,200 miles (1,920 kilometers) from Guinea to Togo, with the largest reserves in Guinea. Uranium deposits are found in South Africa, Niger, Gabon, Zaire, and Namibia. South Africa alone contains one-half the world's gold reserves. Mineral deposits of gold are also found in Zimbabwe, Zaire, and Ghana.

Kimberlite pipes—vertical, near-cylindrical rock bodies caused by deep melting in the upper mantle of Earth's crust—are the main source of gem and industrial diamonds in Africa. Africa contains 40 percent of

the world's diamond reserves, which are located in South Africa, Botswana, Namibia, Angola, and Zaire.

Major coal deposits exist across northern and southern Africa and in the central African countries of Zaire and Nigeria. Petroleum reserves are high in northern Africa, particularly in Libya, Algeria, Egypt, and Tunisia. Nigeria is the biggest petroleum producer in West Africa, followed by Cameroon, Gabon, and the Congo. Angola contains the chief petroleum reserves in southern Africa.

Modern-day climatic and environmental factors

The impact of humankind upon the African environment has been far-reaching and undeniable. Beginning 2,000 years ago and accelerating to the present day, belts of African woodlands have been cleared of trees and other forest plants, a process known as deforestation. Such environmental destruction has been worsened by the overgrazing of animals and other agricultural abuses. Human-made climate changes, including possible global warming caused by the buildup of human-made carbon dioxide, chlorofluorocarbons (CFCs), and other greenhouse gases, have also damaged the environment.

Deforestation, desertification, and soil erosion pose threats to Africa's artificial lakes and, thereby, the continent's hydroelectric capacity, or ability to produce electricity with water power. Africa has limited water resources, and its multiplying and undernourished populations exert ever-greater demands on farmland that has to be irrigated. Many earth scientists say using more environmentally friendly farming techniques and practicing population control are vital to stabilizing Africa's ecology and protecting its resources and mineral wealth.

Africa The second largest continent, extending south from the Mediterranean Sea and bounded by the Atlantic and Indian oceans and the Red Sea.

Physical

The Equator passes through the middle of Africa, so that all but the very north and south are tropical, although regional differences in climate and landscape are vast. Most of northern Africa is desert, the only significant waterway being the Nile. The west, watered by the Niger and other rivers, is rich in tropical forests, though in many coastal regions there is only swamp. Inland, the ground rises first to savannahs and then to hilly, wooded plateaux in the centre of the continent. Here are some of the largest copper deposits in the world, and also deposits of gold, diamonds, uranium, cobalt, and other minerals. East Africa is a temperate region of great lakes, mountains, and high plateaux. It is split from north to south by the Great Rift Valley. South of the Zambezi River are more highlands, giving way in the south-west to the Kalahari Desert. Then the land rises again, to the temperate veld. This good farming country is very rich in minerals. The southernmost coastal plain is ideal for fruit and plantation crops.

History

Evidence suggests that Africa was the birthplace of the human race, as shown by finds at Olduvai Gorge and other sites. By the late Stone Age Proto-Berbers inhabited the north, Ethiopians the Nile valley, while NEGROID peoples moved southwards. Pygmies occupied the central forest, and San and Khoikhoi (called Bushmen and Hottentots by white colonists) roamed the south.

By the 4th millennium BC, one of the world's oldest civilizations had developed in EGYPT. In the north PHOENICIANS, and then CARTHAGINIANS, organized sea-borne empires which fell, with Egypt, to Rome in the last centuries BC. Indigenous kingdoms arose in NUBIA and AKSUM. In the 7th century the Arabs seized the north, bringing to it the religion and culture of ISLAM.

In Cameroon c.500 BC a population explosion sent the Bantu eastwards. They slowly occupied most of southern and central Africa, overwhelming the San people. There and in West Africa chieftainships developed, and some empires with sophisticated cultures, especially in Islamic states such as MALI and in Christian ETHIOPIA. Their intricate system of commerce reached from the Mediterranean to Indonesia and China. The Portuguese arrival in the 15th century heralded European intervention in Africa, stimulating trade in the west and centre, but interrupting it in the east. In the 16th century the north fell to the Ottomans, while south of the Sahara Europeans began the SLAVE TRADE to the Americas. From the 16th to the 18th century in the present Democratic Republic of the Congo (formerly Zaïre) and in central Africa Bantu states developed, some of them sizeable empires. During this period the Bantu were pushing their way southwards, but it was not until the 19th century that they began to form recognizable states in the present South Africa. While each tribe or state developed its individual pattern of constitution, some more sophisticated than others, power was generally concentrated in the hands of chieftains and regulated both by tribal conventions and by free public discussion in tribal assemblies.

During the 19th century the interior was gradually opened up to European explorers, traders, and missionaries in an extensive programme of colonization. Imperialist sentiments and the desire to exploit the continent's natural resources produced a series of military campaigns against the local states and tribes. After World War I Germany's former colonial empire was divided among the victorious Allies. After 1945 the rise of African nationalism accelerated the process of decolonization, most of the Black countries becoming independent between 1957 and 1980, sometimes as a result of peaceful negotiation and sometimes through armed rebellion. In Namibia (until 1990) and South Africa (until 1994), small White élites held on to political power, but elsewhere the descendants of the original inhabitants assumed responsibility for their own government. The artificial boundaries imposed by colonialism, the rapidity of the transition to home rule, and the underdeveloped state of many of the local economies produced political, social, and economic problems of varying severity all over the continent. Many of the new nations remained unstable and politically impoverished, while drought in the 1980s and early 1990s, in both East and Southern Africa, caused terrible suffering. Multiparty democracies, which replaced single-party regimes in many African countries in the early 1990s, inherited vast burdens of World Bank and IMF debt.

Africa Second-largest continent (after Asia), straddling the Equator and lying largely within the tropics.

Land

Africa forms a plateau between the Atlantic and Indian Oceans. Its highest features include the Atlas mountains and Ahaggar mountains in the nw, the Ethiopian Highlands in the e, the Drakensberg mountains in the s, and Mount Kilimanjaro. Lake Assal in the Afar Depression of Djibouti is the lowest point at −153m (−502ft). The huge sunken strip in the e is the African section of the Great Rift Valley. The Sahara stretches across the n, while the Kalahari and Namib are smaller deserts in the s and sw. Madagascar lies off the se coast.

Structure and geology

Africa is composed largely of ancient metamorphic rocks overlain with tertiary Mesozoic and Palaeozoic sediments. The mountains of the nw are folded sedimentary material, roughly contemporaneous with the Alps. The Great Rift Valley, formed by the progressive movement of the Arabian Peninsula away from Africa, is mainly igneous in the n and older pre-Cambrian in the s.

Lakes and rivers

The Rift Valley contains lakes Albert, Malawi, and Tanganyika. Lake Victoria to the e is Africa's largest lake; Lake Chad which shrinks to a salt pan in dry periods, lies in the s Sahara. Rivers include the Nile, Niger, Congo, and Zambezi.

Climate and vegetation

Much of the continent is hot and (outside the desert areas) humid. The belt along the Equator receives more than 250cm (100in) of precipitation a year and is covered by tropical rainforest. The forest gives way both in the n and s to areas of acacia and brush, and then through savanna grassland to desert. The n strip of the continent and the area around the Cape have a Mediterranean climate.

Peoples

Africa is home to more than 13% of the world's population, divided into more than 700 culturally distinct tribes and groups. North of the Sahara Arabs and Berbers predominate, while to the s tribes include the Fulani, Galla, Hausa, Hottentots, Igbo, Masai, Mossi, San, Yoruba, and Zulu. Indians and Europeans also form significant minorities. Africa is relatively thinly populated and c.75% of the population is rural.

Economy

Agriculture is restricted in central Africa by the large expanse of tropical rainforest, although cash crops such as cocoa, rubber, and peanuts are grown on plantations. Along the n coast, crops such as citrus fruits, olives, and cereals are grown. The Sahara is largely unproductive, supporting only a nomadic herding community. East and s Africa are the richest agricultural areas. Apart from South Africa, the entire continent is industrially underdeveloped. Mining is the most important industry. Zambia has the world's largest deposits of copper ore. Bauxite is extracted in w Africa, and oil is produced in Nigeria, Libya, and Algeria. South Africa is extremely rich in minerals: gold, diamonds, and coal being the most important.

Recent History

Before the 1880s, Europeans were, except in South Africa, largely confined to the coastal regions. by the end of the 19th century, the whole continent, except for Liberia and Ethiopia, was under foreign domination either by European powers, or (in the n) by the Ottoman Empire. Starting in the 1950s, the colonies secured their independence within the space of 40 years, but this process of rapid decolonization brought unrest and instability to much of Africa. A major cause of unrest was (and continues to be) the artificial boundaries created by colonialism. Lasting democracy proved difficult to achieve in many countries and military rule is prevalent. Area: c.30 million sq km (11.7 million sq mi) Highest mountain Kilimanjaro (Tanzania) 5895m (19,340ft) Longest river Nile 6670km (4140mi) Population 812 million Largest cities Lagos (8,029,200); Cairo (6,789,489); Kinshasa (4,655,313); Alexandria (3,328,196); Casablanca (2,940,623); Algiers (2,561,992) See also articles on individual countries

Africa Following their destruction of Carthage at the conclusion of the Third Punic War in 146 bc, the Romans originally named their province after the Berber tribe of Afrigi, who lived in what is now Tunisia and eastern Algeria. As the Romans increased the size of the province by expanding southwards and eastwards, and then westwards, so the name came to be applied to these additional regions until in time it embraced the whole of the continent. Afrigi may have been derived from the Berber word ʼafar ‘dust’, to mean ‘People from the Dusty Land’. ‘Black Africa’ refers to that part of the continent south of the Sahara where the majority of the population is black.

Africa ♀ Name recorded in the U.S. since the 18th century and now favoured by African Americans conscious of their ancestral heritage.

AFRICA

This entry includes four subentries:
Central Africa
East Africa
North Africa
West Africa

AFRICA

This entry contains two subentries:

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