Salient features of world’s physical geography
The Earth is the largest and most massive of the rocky inner planets, although it is dwarfed by the gas giants beyond the Asteroid Belt.
Earth’s interior is a complex structure of superheated rocks. Most geologists recognize three major layers: the dense core, the bulky mantle, and the brittle crust. No one has ever ventured below Earth’s crust.
The Earth’s core is mostly made of iron and nickel. It consists of a solid center surrounded by an outer layer of liquid. The core is found about 2,900 kilometers (1,802 miles) below Earth’s surface, and has a radius of about 3,485 kilometers (2,165 miles).
A mantle of heavy rock (mostly silicates) surrounds the core. The mantle is about 2,900 kilometers (1,802 miles) thick, and makes up a whopping 84% of Earth’s total volume. Parts of the mantle are molten, meaning they are composed of partly melted rock. The mantle’s molten rock is constantly in motion. It is forced to the surface during volcanic eruptions and at mid-ocean ridges.
Earth’s crust is the planet’s thinnest layer, accounting for just 1% of Earth’s mass. There are two kinds of crust: thin, dense oceanic crust and thick, less-dense continental crust. Oceanic crust extends about 5 to 10 kilometers (3 to 6 miles) beneath the ocean floor. Continental crust is about 35 to 70 kilometers (22 to 44 miles) thick.
Exterior: Tectonic Activity
The crust is covered by a series of constantly moving tectonic plates. New crust is created along mid-ocean ridges and rift valleys, where plates pull apart from each other in a process called rifting. Plates slide above and below each other in a process called subduction. They crash against each other in a process called faulting.
Tectonic activity such as subduction and faulting has shaped the crust into a variety of landscapes. Earth’s highest point is Mount Everest, Nepal, which soars 8,850 kilometers (29,035 feet) in the Himalaya Mountains in Asia. Mount Everest continues to grow every year, as subduction drives the Indo-Australian tectonic plate below the Eurasian tectonic plate. Subduction also creates Earth’s deepest point, the Mariana Trench, about 11 kilometers (6.9 miles) below the surface of the Pacific Ocean. The heavy Pacific plate is being subducted beneath the small Mariana plate.
Plate tectonics are also responsible for landforms such as geysers, earthquakes, and volcanoes. Tectonic activity around the Pacific plate, for instance, creates “Ring of Fire.” This tectonically active area includes volcanoes such as Mount Fuji, Japan, and earthquake-prone fault zones such as the west coast of the United States.
Earth’s physical environment is often described in terms of spheres: the magnetosphere, the atmosphere, the hydrosphere, and the lithosphere. Parts of these spheres make up the biosphere, the area of Earth where life exists.
Earth’s magnetosphere describes the pocket of space surrounding our planet where charged particles are controlled by Earth’s magnetic field.
The charged particles that interact with Earth’s magnetosphere are called the solar wind. The pressure of the solar wind compresses the magnetosphere on the “dayside” of Earth to about 10 Earth radii. The long tail of the magnetosphere on the “nightside” of Earth stretches to hundreds of Earth radii. The most well-known aspect of the magnetosphere are the charged particles that sometimes interact over its poles—the auroras, or Northern and Southern Lights.
Earth’s atmosphere is a blanket of gases enveloping the Earth and retained by our planet’s gravity. Atmospheric gases include nitrogen, water vapor, oxygen, and carbon dioxide.
The atmosphere is responsible for temperature and other weather patterns on Earth. It blocks most of the sun’s ultraviolet radiation (UV), conducts solar radiation and precipitation through constantly moving air masses, and keeps our planet’s average surface temperature to about 15° Celsius (59° Fahrenheit).
The atmosphere has a layered structure. From the ground toward the sky, the layers are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Up to 75% of the total mass of the atmosphere is in the troposphere, where most weather occurs. The boundaries between the layers are not clearly defined, and change depending on latitude and season.
The hydrosphere is composed of all the water on Earth. Nearly three-fourths of the Earth is covered in water, most of it in the ocean. Less 3% of the hydrosphere is made up of freshwater. Most freshwater is frozen in ice sheets and glaciers in Antarctica, the North American island of Greenland, and the Arctic. Freshwater can also be found underground, in chambers called aquifers, as well as rivers, lakes, and springs.
Water also circulates around the world as vapor. Water vapor can condenseinto clouds and fall back to Earth as precipitation.
The hydrosphere helps regulate the Earth’s temperature and climate. The ocean absorbs heat from the sun and interacts with the atmosphere to move it around the Earth in air currents.
The lithosphere is Earth’s solid shell. The crust and the upper portion of the mantle form the lithosphere. It extends from Earth’s surface to between 50 and 280 kilometers (31 to 174 miles) below it. The difference in thickness accounts for both thin oceanic and thicker continental crust.
The rocks and minerals in Earth’s lithosphere are made of many elements. Rocks with oxygen and silicon, the most abundant elements in the lithosphere, are called silicates. Quartz is the most common silicate in the lithosphere—and the most common type of rock on Earth.
Cycles on Earth
Almost all materials on Earth are constantly being recycled. The three most common cycles are the water cycle, the carbon cycle, and the rock cycle.
- Water Cycle
The water cycle involves three main phases, related to the three states of water: solid, liquid, and gas. Ice, or solid water, is most common near the poles and at high altitudes. Ice sheets and glaciers hold the most solid water.
Ice sheets and glaciers melt, transforming into liquid water. The most abundant liquid water on the planet is in the ocean, although lakes, rivers, and underground aquifers also hold liquid water. Life on Earth is dependent on a supply of liquid water. Most organisms, in fact, are made up mostly of liquid water, called body water. The human body is about 50% to 60% body water. In addition to survival and hygiene, people use liquid water for energy and transportation.
The third phase of the water cycle occurs as liquid water evaporates. Evaporation is the process of a liquid turning into a gas, or vapor. Water vapor is invisible and makes up part of the atmosphere. As water vapor condenses, or turns back into liquid, pockets of vapor become visible as clouds and fog. Eventually, clouds and fog become saturated, or full of liquid water. This liquid water falls to Earth as precipitation. It can then enter a body of water, such as an ocean or lake, or freeze and become part of a glacier or ice sheet. The water cycle starts again.
- Carbon Cycle
The carbon cycle involves the exchange of the element carbon through the Earth’s atmosphere, hydrosphere, and lithosphere. Carbon, essential for all life on Earth, enters the biosphere many ways. Carbon is one of the gases that make up the atmosphere. It is also ejected during the eruption of volcanoes and ocean vents.
All living or once-living materials contain carbon. These materials are organic. Plants and other autotrophs depend on carbon dioxide to create nutrients in a process called photosynthesis. These nutrients contain carbon. Animals and other organisms that consume autotrophs obtain carbon. Fossil fuels, the remains of ancient plants and animals, contain very high amounts of carbon.
As organisms die and decompose, they release carbon into the ocean, soil, or atmosphere. Plants and other autotrophs use this carbon for photosynthesis, starting the carbon cycle again.
3. Rock Cycle
The rock cycle is a process that explains the relationship between the three main types of rocks: igneous, sedimentary, and metamorphic. Unlike water in the water cycle and or carbon in the carbon cycle, not all rocks are recycled in different forms. There are some rocks that have been in their present form since soon after the Earth cooled. These stable rock formations are called cratons.
Igneous rocks are formed as lava hardens. Lava is molten rock ejected by volcanoes during eruptions. Granite and basalt are common types of igneous rocks. Igneous rocks can be broken apart by the forces of erosion and weathering. Winds or ocean currents may then transport these tiny rocks (sand and dust) to a different location.
Sedimentary rocks are created from millions of tiny particles slowly building up over time. Igneous rocks can become sedimentary by collecting with other rocks into layers. Sedimentary rocks include sandstone and limestone.
Metamorphic rocks are formed when rocks are subjected to intense heat and pressure. The rocks change (undergo metamorphosis) to become a new type of rock. Marble, for example, is a metamorphic rock created from rock that was once limestone, a sedimentary rock.
Physical Geography is a sub-discipline of two much larger fields of study – Geography and Earth Sciences. The main purpose of Physical Geography is to explain the spatial characteristics of the various natural phenomena associated with the Earth’s hydrosphere, biosphere, atmosphere, and lithosphere.
Physical geography focuses upon the character of, and processes shaping, the land-surface of the Earth and its envelope, emphasizes the spatial variations that occur and the temporal changes necessary to understand the contemporary environments of the Earth. Its purpose is to understand how the Earth’s physical environment is the basis for, and is affected by, human activity. Physical geography was conventionally subdivided into geomorphology, climatology, hydrology, and biogeography, but is now more holistic in systems analysis of recent environmental and Quaternary change. It uses expertise in mathematical and statistical modelling and in remote sensing, develops research to inform environmental management and environmental design, and benefits from collaborative links with many other disciplines such as biology (especially ecology), geology and engineering.
North America, the third-largest continent, extends from the tiny Aleutian Islands in the northwest to the Isthmus of Panama in the south. The continent includes the enormous island of Greenland in the northeast and the small island countries and territories that dot the Caribbean Sea and western North Atlantic Ocean. In the far north, the continent stretches halfway around the world, from Greenland to the Aleutians. But at Panama’s narrowest part, the continent is just 50 kilometers (31 miles) across.
North America’s physical geography, environment and resources, and human geography can be considered separately. North America can be divided into five physical regions: the mountainous west, the Great Plains, the Canadian Shield, the varied eastern region, and the Caribbean. Mexico and Central America’s western coast are connected to the mountainous west, while its lowlands and coastal plains extend into the eastern region.
Within these regions are all the major types of biomes in the world. A biomeis a community of animals and plants spreading over an extensive area with a relatively uniform climate. Some diverse biomes represented in North America include desert, grassland, tundra, and coral reefs.
Young mountains rise in the west. The most familiar of these mountains are probably the Rockies, North America’s largest chain. The Rockies stretch from the province of British Columbia, Canada, to the U.S. state of New Mexico.
The Rocky Mountains are part of a system of parallel mountain ranges known as the Cordilleras. A cordillera is a long series of mountain ranges. Although cordilleras exist all over the world, in North America, “the Cordilleras” indicate the massive mountain ranges in the western part of the continent. The Cordilleras extend from Canada all the way to the Isthmus of Panama.
Volcanic mountain ranges in Guatemala, Honduras, Nicaragua, Costa Rica, and Panama are also considered part of the Cordilleras. Volcanic eruptions and earthquakes occur frequently in this region. Volcanic activity can destroy towns and cities. It also contributes to the rich, fertile soils of the region.
The temperate rain forest supports a wide variety of life. The Sitka spruce, western red cedar, and Douglas fir are trees native to North America’s temperate rain forest. Some of these trees grow to more than 90 meters (300 feet) tall and 3 meters (10 feet) in diameter. Black bears, Roosevelt elk, and marmots are indigenous animal species.
The three major desert regions of North America—the Sonoran, Mojave, and Chihuahuan—are all in the American southwest and northern Mexico. These large deserts are located in the rain shadows of nearby mountains. The mountains block precipitation and accelerate the movement of hot, dry windover these regions. The Sonoran is in the rain shadow of the Coast Ranges, the Mojave is in the shadow of the Sierra Nevada, and the Chihuahuan is in the shadow of the Sierra Madre.
Notable desert plant species includes the saguaro cactus, Joshua tree, and mesquite. Animal species include the roadrunner, Gila monster, and rattlesnake.
In addition to mountains, deserts, and forests, the northern part of the western region of North America also has the richest deposits of oil and natural gas on the continent. Most of these deposits are located offshore, in the Arctic and Pacific Oceans.
The Great Plains lie in the middle of the continent. Deep, rich soil blankets large areas of the plains in Canada and the United States. Grain grown in this region, called the “Breadbasket of North America,” feeds a large part of the world. The Great Plains are also home to rich deposits of oil and natural gas.
The Canadian Shield is a raised but relatively flat plateau. It extends over eastern, central, and northwestern Canada. The Canadian Shield is characterized by a rocky landscape pocked by an astounding number of lakes.
The tundra, stretching along the northern borders of Alaska and Canada to the Hudson Bay area, is a biome common to the Canadian Shield. Tundra is where low temperatures and precipitation levels hinder tree growth. The tundra is characterized by permafrost—soil that is frozen for two or more years. This permafrost keeps moisture near the soil’s surface, promoting vegetation growth even in the extreme, Arctic conditions of the tundra.
North America’s older mountain ranges, including the Appalachians, rise near the east coast of the United States and Canada. These areas have been mined for rich deposits of coal and other minerals for hundreds of years.
The Atlantic coastal plain extends from river, marsh, and wetland regions east of the mountains toward the sandy beaches of the Atlantic coast. Wetland areas are a biome of the eastern region and consist of areas of land whose soil is saturated with permanent or seasonal moisture. The Florida Everglades is the largest wetland system in the United States, covering more than 11,137 square kilometers (4,300 square miles) of southern Florida.
The Caribbean Region includes more than 7,000 islands, islets, reefs, and cays. The region’s islands and smaller islets are varied in their topography; some have relatively flat and sandy terrain while others are rugged, mountainous, and volcanic.
The coral reefs and cays of the Caribbean Sea are among the most spectacular biomes in North America. A reef is a ridge of jagged rock, coral, or sand just above or below the surface of the sea. Some coral reefs surround islands, such as the Bahamas, Antigua, and Barbados. Others are found off the Florida Keys, a chain of cays—small islands situated on a coral reef platform—near the southern coast of the U.S. state of Florida.
North America’s varied landscape features many natural wonders. It has deep canyons, such as Copper Canyon in the Mexican state of Chihuahua. Denali, the continent’s highest peak, stands at 6,194 meters (20,320 feet) within Denali National Park and Preserve in the U.S. state of Alaska. Yellowstone National Park, in the U.S. states of Wyoming, Montana, and Idaho, has some of the world’s most active geysers. Canada’s Bay of Fundy has the greatest tidal range in the world. The Great Lakes form the planet’s largest area of freshwater. The Mississippi River, at 3,730 kilometers (2,320 miles) long, is one of the longest river systems in the world and drains all or parts of 31 U.S. states.
South America, the fourth-largest continent, extends from the Gulf of Darién in the northwest to the archipelago of Tierra del Fuego in the south.
South America can be divided into three physical regions: mountains and highlands, river basins, and coastal plains. Mountains and coastal plains generally run in a north-south direction, while highlands and river basins generally run in an east-west direction.
South America’s extreme geographic variation contributes to the continent’s large number of biomes. A biome is a community of animals and plants that spreads over an area with a relatively uniform climate.
Within a few hundred kilometers, South America’s coastal plains’ dry desert biome rises to the rugged alpine biome of the Andes mountains. One of the continent’s river basins (the Amazon) is defined by dense, tropical rain forest, while the other (Paraná) is made up of vast grasslands.
South America’s primary mountain system, the Andes, is also the world’s longest. The range covers about 8,850 kilometers (5,500 miles). Situated on the far western edge of the continent, the Andes stretch from the southern tip to the northernmost coast of South America. There are hundreds of peaks more than 4,500 meters (15,000 feet) tall, many of which are volcanic.
The highest peak in the Andes, Aconcagua, stands at 6,962 meters (22,841 feet) and straddles the Argentina-Chile border. Aconcagua is the tallest mountain outside Asia.
High plateaus are also a feature of the Andes. The altiplano of Peru and Bolivia, for example, has an elevation of about 3,700 meters (12,300 feet). The Patagonia region of Argentina and Chile consists of lower-elevation plateaus and rugged glaciers.
Most plants in the alpine biome are small, and their leaves are stiff and strong to protect them from frost and drought. The largest herb in the world, Puya raimondii, is known as the Queen of the Andes. A Puya raimondiican live for 100 years and can grow to more than 9 meters (30 feet) tall. The leaves of this endangered species all grow from one woody stem, allowing moisture to run down the leaves to the base of the plant.
Outside the Andes, South America has two principal highland areas: the Brazilian Highlands and the Guiana Highlands. Located south of the Amazon River in Brazil, the Brazilian Highlands are made up of low mountains and plateaus that rise to an average elevation of 1,006 meters (3,300 feet). The Guiana Highlands are located between the Amazon and Orinoco Rivers. The heavily forested plateau of the Guiana Highlands covers southern Venezuela, French Guiana, Guyana, northern Brazil, and a portion of southeastern Colombia.
South America has three important river basins: the Amazon, Orinoco, and Paraguay/Paraná. The Amazon River basin has an area of almost 7 million square kilometers (2.7 million square miles), making it the largest watershed in the world. The basin, which covers most of northern South America, is fed by tributaries from the glaciers of the Andes. Every second, the Amazon River empties 209,000 cubic meters (7,381,000 cubic feet) of freshwater into the Atlantic Ocean.
The Amazon River is the life force of the equally vast Amazon rain forest, which makes up about half of the rain forest of the entire planet. This tropicalbiome has as many as 100 different tree species on a single acre, including the rubber tree, silk cotton tree, and Brazil nut tree. Other important plant species include palms, ferns, and ropelike vines known as lianas that network throughout the rain forest’s dense canopy.
The diversity of animal life in the Amazon rain forest is unsurpassed in the rest of the world. The rain forest is perfectly suited for arboreal, or tree-living, animals. More than 2 million species of insects are native to the region, including hundreds of spiders and butterflies. Primates are abundant—howler monkeys, spider monkeys, and capuchin monkeys—along with sloths, snakes, and iguanas. Thousands of native birds include brightly colored macaws, parrots, toucans, and parakeets.
The Paraguay/Paraná River basin covers almost 2.8 million square kilometers (1,081,000 square miles), which is much of southeastern Brazil and Bolivia, Paraguay, and northern Argentina. The Paraná River includes Iguazu Falls, a massive series of waterfalls that extend for 2.7 kilometers (1.7 miles).
South American coastal plains are found on the northeastern coast of Brazil, on the Atlantic Ocean, and the western, Pacific coast of Peru and Chile. The coastal plains of northeastern Brazil are extremely dry. The Brazilian Highlands act as a wedge that pushes moist sea winds away from the coastal plains.
The western coastal plains are also extremely dry. They are trapped between the cold Peru Current to the west and the Andes Mountains to the east. The Peru Current brings cold water to the Pacific coast of Peru and Chile. This cold surface water results in thermal inversion: cold air at sea level and stable, warmer air higher up. Thermal inversion produces a thick layer of clouds at low altitudes. These low-lying clouds blanket much of the Pacific coast of South America. They do not allow precipitation to form.
Africa physical geography
Africa, the second-largest continent, is bounded by the Mediterranean Sea, the Red Sea, the Indian Ocean, and the Atlantic Ocean. It is divided in half almost equally by the Equator.
Africa has eight major physical regions: the Sahara, the Sahel, the Ethiopian Highlands, the savanna, the Swahili Coast, the rain forest, the African Great Lakes, and Southern Africa. Some of these regions cover large bands of the continent, such as the Sahara and Sahel, while others are isolated areas, such as the Ethiopian Highlands and the Great Lakes. Each of these regions has unique animal and plant communities.
The Sahara is the worlds largest hot desert, covering 8.5 million square kilometers (3.3 million square miles), about the size of the South American country of Brazil. Defining Africas northern bulge, the Sahara makes up 25 percent of the continent.
The Sahara has a number of distinct physical features, including ergs, regs, hamadas, and oases. Ergs, which cover 20 percent of the Sahara, are sand dunes that stretch for hundreds of kilometers at heights of more than 300 meters (1,000 feet). Ergs cover most of Algeria and Libya and parts of Mali and Nigeria. Ergs can contain large quantities of salt, which is sold for industrial and food use.
Regs are plains of sand and gravel that make up 70 percent of the Sahara. The gravel can be black, red, or white. Regs are the remains of prehistoric seabeds and riverbeds, but are now nearly waterless.
Hamadas are elevated plateaus of rock and stone that reach heights of 3,353 meters (11,000 feet). They include the Atlas Mountains, which stretch from southwestern Morocco to northeastern Tunisia; the Tibesti Mountains of southern Libya and northern Chad; and the Ahaggar Mountains in southern Algeria.
Saharan plants survive thanks to root systems that plunge as far as 24 meters (80 feet) underground. In parts of the Sahara, plants cannot take root at all. In the southern Libyan Desert, for instance, no greenery exists for more than 195 kilometers (120 miles).
The Sahel is a narrow band of semi-arid land that forms a transition zone between the Sahara to the north and the savannas to the south. It is made up of flat, barren plains that stretch roughly 5,400 kilometers (3,300 miles) across Africa, from Senegal to Sudan.
The Sahel contains the fertile delta of the Niger, one of Africas longest rivers. Unfortunately, the Sahels fertile land is rapidly becoming desert as a result of drought, deforestation, and intensive agriculture. This process is known as desertification.
The Ethiopian Highlands began to rise 75 million years ago, as magma from Earths mantle uplifted a broad dome of ancient rock. This dome was later split as Africas continental crust pulled apart, creating the Great Rift Valley system. Today, this valley cuts through the Ethiopian Highlands from the southwest to the northeast. The Ethiopian Highlands are home to 80 percent of Africas tallest mountains.
The highlands craggy landscape is perfect for nimble animal species. Native species such as the walia ibex, an endangered wild goat, and the gelada baboon live in the ledges and rocky outposts of the Simien Mountains. The most emblematic highlands species is probably the Ethiopian wolf, which is now on the brink of extinction.
Savannas, or grasslands, cover almost half of Africa, more than 13 million square kilometers (5 million square miles). These grasslands make up most of central Africa, beginning south of the Sahara and the Sahel and ending north of the continents southern tip.
The Swahili Coast stretches about 1,610 kilometers (1,000 miles) along the Indian Ocean, from Somalia to Mozambique. The nearby coral reefs and barrier islands protect the coast from severe weather.
There is not a lot of animal life on the sandy Swahili Coast. The golden-rumped elephant shrew, an insect-eating rodent with a long snout, is common. A small, primitive species of primate known as the bush baby inhabits vegetated areas of the Swahili Coast. Bush babies, which have enormous eyes for hunting at night, feed primarily on insects, fruit, and leaves.
Most of Africas native rain forest has been destroyed by development, agriculture, and forestry. Today, 80 percent of Africas rain forest is concentrated in central Africa, along the Congo River basin.
Africas rain forests have a rich variety of animal life; a 6-kilometer (4-mile) patch could contain up to 400 bird species, 150 butterfly species, and 60 species of amphibians. Important mammals include African forest elephants, gorillas, the black colobus monkey, and the okapi, a donkey-like giraffe.
The driver ant is one of Africas most aggressive rain forest species. Driver ants move in columns of up to 20 million across the rain forest floor, and will eat anything from toxic millipedes to reptiles and small mammals.
There are seven major African Great Lakes: Lake Albert, Lake Edward, Lake Kivu, Lake Malawi, Lake Tanganyika, Lake Turkana, and Lake Victoria. Lake Victoria, the largest lake in Africa, is the southern source of the Nile River, the longest river in the world.
The African Great Lakes region has a diverse range of aquatic and terrestrialanimal life. Fish include the 45-kilogram (100-pound) Nile perch and the 2.5-centimeter (1-inch) cichlid. Migrating savanna animals, such as wildebeest, use the lakes as watering holes. Hippos and crocodiles call the region their home.
The Great Lakes abut everything from rain forest to savanna plant communities. However, invasive species like the water hyacinth and papyrus have begun to take over entire shorelines, endangering animals and plants.
Asia Physical Geography
Asia is the largest of the world’s continents, covering approximately 30 percent of the Earth’s land area. It is also the world’s most populous continent, with roughly 60 percent of the total population.
Asia makes up the eastern portion of the Eurasian supercontinent; Europe occupies the western portion. The border between the two continents is debated. However, most geographers define Asia’s western border as an indirect line that follows the Ural Mountains, the Caucasus Mountains, and the Caspian and Black Seas. Asia is bordered by the Arctic, Pacific, and Indian Oceans.
Asia can be divided into five major physical regions: mountain systems; plateaus; plains, steppes, and deserts; freshwater environments; and saltwater environments.
The Himalaya mountains extend for about 2,500 kilometers (1,550 miles), separating the Indian subcontinent from the rest of Asia. The Indian subcontinent, once connected to Africa, collided with the Eurasian continent about 50 million to 55 million years ago, forming the Himalayas. The Indian subcontinent is still crashing northward into Asia, and the Himalayas are growing about 5 centimeters (2 inches) every year.
The Tien Shan mountain system stretches for about 2,400 kilometers (1,500 miles), straddling the border between Kyrgyzstan and China. The name Tien Shan means “Celestial Mountains” in Chinese. The two highest peaks in the Tien Shan are Victory Peak, which stands at 7,439 meters (24,406 feet), and Khan Tängiri Peak, which stands at 6,995 meters (22,949 feet). Tien Shan also has more than 10,100 square kilometers (3,900 square miles) of glaciers. The largest glacier is Engil’chek Glacier, which is about 60 kilometers (37 miles) long.
The Ural Mountains run for approximately 2,500 kilometers (1,550 miles) in an indirect north-south line from Russia to Kazakhstan. The Ural Mountains are some of the world’s oldest, at 250 million to 300 million years old.
Asia is home to many plateaus, areas of relatively level high ground. The Iranian plateau covers more than 3.6 million square kilometers (1.4 million square miles), encompassing most of Iran, Afghanistan, and Pakistan. The plateau is not uniformly flat, but contains some high mountains and low river basins. The highest mountain peak is Damavand, at 5,610 meters (18,410 feet). The plateau also has two large deserts, the Dasht-e Kavir and Dasht-e Lut.
The Deccan Plateau makes up most of the southern part of India. The plateau’s average elevation is about 600 meters (2,000 feet). It is bordered by three mountain ranges: the Satpura Range in the north, and the Eastern and Western Ghats on either side. The plateau and its main waterways—the Godavari and Krishna rivers—gently slope toward the Eastern Ghats and the Bay of Bengal.
The Tibetan Plateau is usually considered the largest and highest area ever to exist in the history of Earth. Known as the “Rooftop of the World,” the plateau covers an area about half the size of the contiguous United States and averages more than 5,000 meters (16,400 feet) above sea level. The Tibetan Plateau is extremely important to the world’s water cycle because of its tremendous number of glaciers. These glaciers contain the largest volume of ice outside the poles. The ice and snow from these glaciers feed Asia’s largest rivers. Approximately 2 billion people depend on the rivers fed by the plateau’s glaciers.
The West Siberian Plain, located in central Russia, is considered one of the world’s largest areas of continuous flatland. It extends from north to south about 2,400 kilometers (1,500 miles) and from west to east about 1,900 kilometers (1,200 miles). With more than 50 percent of its area at less than 100 meters (330 feet) above sea level, the plain contains some of the world’s largest swamps and flood plains.
Central Asia is dominated by a steppe landscape, a large area of flat, unforested grassland. Mongolia can be divided into different steppe zones: the mountain forest steppe, the arid steppe, and the desert steppe. These zones transition from the country’s mountainous region in the north to the Gobi Desert on the southern border with China.
The Rub’ al Khali desert, considered the world’s largest sand sea, covers an area larger than France across Saudi Arabia, Oman, the United Arab Emirates, and Yemen. It holds roughly half as much sand as Africa’s Sahara desert, even though it is 15 times smaller in size. The desert is known as the Empty Quarter because it is virtually inhospitable to humans except for Bedouin tribes that live on its edges.
Lake Baikal, located in southern Russia, is the deepest lake in the world, reaching a depth of 1,620 meters (5,315 feet). The lake contains 20 percent of the world’s unfrozen freshwater, making it the largest reservoir on Earth. It is also the world’s oldest lake, at 25 million years old.
The Yangtze is the longest river in Asia and the third longest in the world (behind the Amazon of South America and the Nile of Africa). Reaching 6,300 kilometers (3,915 miles) in length, the Yangtze moves east from the glaciers of the Tibetan Plateau to the river’s mouth on the East China Sea. The Yangtze is considered the lifeblood of China. It drains one-fifth of the country’s land area, is home to one-third of its population, and contributes greatly to China’s economy.
The Tigris and Euphrates Rivers begin in the highlands of eastern Turkey and flow through Syria and Iraq, joining in the city of Qurna, Iraq, before emptying into the Persian Gulf. The land between the two rivers, known as Mesopotamia, was the center of the earliest civilizations, including Sumerand the Akkadian Empire. Today, the Tigris-Euphrates river system is under threat from increased agricultural and industrial use. These pressures have caused desertification and increased salts in the soil, severely damaging local watershed habitats.
The Bay of Bengal is the largest bay in the world, covering almost 2.2 million square kilometers (839,000 square miles) and bordering Bangladesh, India, Sri Lanka, and Burma. Many large rivers, including the Ganges and Brahmaputra, empty into the bay. The briny wetlands formed by the Ganges-Brahmaputra on the Bay of Bengal is the largest delta in the world.
Asia’s diverse physical and cultural landscape has dictated the way animals have been domesticated. In the Himalayas, communities use yaks as beasts of burden. Yaks are large animals related to cattle, but with a thick fiber coat and the ability to survive in the oxygen-poor high altitude of the mountains. Yaks are not only used for transportation and for pulling plows, but their coats are sources of warm, hardy fiber. Yak milk is used for butter and cheese.
In the Mongolian steppe, the two-humped Bactrian camel is the traditional beast of burden. Bactrian camels are critically endangered in the wild. The camel’s humps store nutrient-rich fat, which the animal can use in times of drought, heat, or frost. Its size and ability to adapt to hardship make it an ideal pack animal. Bactrians can actually outrun horses over long distances. These camels were the traditional animals used in caravans on the Silk Road, the legendary trade route linking eastern Asia with India and the Middle East.
The freshwater and marine habitats of Asia offer incredible biodiversity. Lake Baikal’s age and isolation make it a unique biological site. Aquatic life has been able to evolve for millions of years relatively undisturbed, producing a rich variety of flora and fauna. The lake is known as the “Galápagos of Russia” because of its importance to the study of evolutionary science. It has 1,340 species of animals and 570 species of plants.
Hundreds of Lake Baikal’s species are endemic, meaning they are found nowhere else on Earth. The Baikal seal, for instance, is one of the few freshwater seal species in the world. The Baikal seal feeds primarily on the Baikal oil fish and the omul. Both fishes are similar to salmon, and provide fisheries for the communities on the lake.
The Bay of Bengal, on the Indian Ocean, is one of the world’s largest tropical marine ecosystems. The bay is home to dozens of marine mammals, including the bottlenose dolphin, spinner dolphin, spotted dolphin, and Bryde’s whale. The bay also supports healthy tuna, jack, and marlin fisheries.
Sundarbans is a huge mangrove forest. Mangroves are hardy trees that are able to withstand the powerful, salty tides of the Bay of Bengal as well as the freshwater flows from the Ganges and Brahamaputra. In addition to mangroves, the Sundarbans is forested by palm trees and swamp grasses.
The swampy jungle of the Sundarbans supports a rich animal community. Hundreds of species of fish, shrimp, crabs, and snails live in the exposed root system of the mangrove trees. The Sundarbans supports more than 200 species of aquatic and wading birds. These small animals are part of a food web that includes wild boar, macaque monkeys, monitor lizards, and a healthy population of Bengal tigers.
Oceania is a region made up of thousands of islands throughout the Central and South Pacific Ocean. It includes Australia, the smallest continent in terms of total land area. Most of Australia and Oceania is under the Pacific, a vast body of water that is larger than all the Earth’s continental landmasses and islands combined. The name “Oceania” justly establishes the Pacific Ocean as the defining characteristic of the continent.
Oceania is dominated by the nation of Australia. The other two major landmasses of Oceania are the microcontinent of Zealandia, which includes the country of New Zealand, and the western half of the island of New Guinea, made up of the nation of Papua New Guinea. Oceania also includes three island regions: Melanesia, Micronesia, and Polynesia (including the U.S. state of Hawaii).
Oceania can be divided into three island groups: continental islands, high islands, and low islands. The islands in each group are formed in different ways and are made up of different materials. Continental islands have a variety of physical features, while high and low islands are fairly uniform in their physical geography.
Continental islands were once attached to continents before sea level changes and tectonic activity isolated them. Tectonic activity refers to the movement and collision of different sections, or plates, of the Earth’s crust.
Australia, Zealand, and New Guinea are continental islands. These three regions share some physical features. All three have mountain ranges or highlands—the Great Dividing Range in Australia; the North Island Volcanic Plateau and Southern Alps in New Zealand; and the New Guinea Highlands in Papua New Guinea. These highlands are fold mountains, created as tectonic plates pressed together and pushed land upward. New Zealand and Papua New Guinea also have volcanic features as a result of tectonic activity.
Although they share some landscape features, each of these regions has distinct physical features that resulted from different environmental processes. Australia’s landscape is dominated by the Outback, a region of deserts and semi-arid land. The Outback is a result of the continent’s large inland plains, its location along the dry Tropic of Capricorn, and its proximity to cool, dry, southerly winds. New Zealand’s glaciers are a result of the islands’ high elevations and proximity to cool, moisture-bearing winds. Papua New Guinea’s highland rain forests are a result of the island’s high elevations, proximity to tropical, moisture-bearing winds, and location right below the warm Equator.
High islands, also called volcanic islands, are created as volcanic eruptions build up land over time. These eruptions begin under water, when hot magma is cooled and hardened by the ocean. Over time, this activity creates islands with a steep central peak—hence the name “high island.” Ridges and valleys radiate outward from the peak toward the coastline.
The island region of Melanesia contains many high islands because it is a major part of the “Ring of Fire,” a string of volcanoes around the boundary of the Pacific Ocean. This part of the Ring of Fire is on the boundary of the Pacific plate and the Australian plate. This is a convergent plate boundary, where the two plates move toward each other. Important volcanic mountains in Melanesia include Mount Tomanivi, Fiji; Mount Lamington, Papua New Guinea; and Mount Yasur, Vanuatu.
Low islands are also called coral islands. They are made of the skeletons and living bodies of small marine animals called corals. Sometimes, coral islands barely reach above sea level—hence the name “low island.” Low islands often take the shape of an irregular ring of very small islands, called an atoll, surrounding a lagoon. An atoll forms when a coral reef builds up around a volcanic island, then the volcanic island erodes away, leaving a lagoon. Atolls are defined as one island even though they are made up of multiple communities of coral.
The island regions of Micronesia and Polynesia are dominated by low islands. The Kwajalein Atoll in the Marshall Islands, for example, is composed of 97 islands and islets that surround one of the largest lagoons in the world, with an area of 2,173 square kilometers (839 square miles). The nation of Kiribati is composed of 32 atolls and one solitary island dispersed over 3.5 million square kilometers (1.35 million square miles) of the Pacific Ocean.
The evolution of flora and fauna across the islands of Australia and Oceania is unique. Many plants and animals reached the islands from southern Asia during the last glacial period, when sea levels were low enough to allow for travel. After sea levels rose, species adapted to the environment of each island or community of islands, producing multiple species that evolved from a common ancestor. Due to its isolation from the rest of the world, Australia and Oceania has an incredibly high number of endemic species, or species that are found nowhere else on Earth.
Plants traveled between islands by riding wind or ocean currents. Birds carried the seeds of fruits and plants and spread them between islands with their droppings. Ferns, mosses, and some flowering plants rely on spores or seeds that can remain airborne for long distances. Coconut palms and mangroves, common throughout Australia and Oceania, produce seeds that can float on salty water for weeks at a time. Important flowering plants native to Australia and Oceania include the jacaranda, hibiscus, pohutukawa, and kowhai. Other indigenous trees include the breadfruit, eucalyptus, and banyan.
Birds are very common in Australia and Oceania because they are one of the few animals mobile enough to move from island to island. There are more than 110 endemic bird species in Australia and Oceania, including many seabirds. Many flightless birds, such as emus, kiwis, cassowaries, wekas, and takahes, are native to Australia, Papua New Guinea, and New Zealand. The Pacific Islands have more than 25 species of birds of paradise, which exhibit colorful plumage.
Lizards and bats make up the majority of Australia and Oceania’s native land animals. Lizard species include the goanna, skink, and bearded dragon. Australia and Oceania has more than a hundred different species of fruit bats.
The few native land animals in Australia and Oceania are unusual. Australia and Oceania is the only place in the world that is home to monotremes—mammals that lay eggs. All monotremes are native to Australia and Papua New Guinea. There are only five living species: the duckbill platypus and four species of echidna.
The marine environment is an important and influential physical region in Australia and Oceania. The region is composed of three marine realms: Temperate Australasia, Central Indo-Pacific, and Eastern Indo-Pacific. Marine realms are large ocean regions where animal and plant life are similar because of shared environmental and evolutionary factors.
The Temperate Australasia realm includes the seas surrounding the southern half of Australia and the islands of New Zealand. This realm is one of the world’s richest areas for seabirds. Its cold, nutrient-rich waters support a diversity of plants and fish that seabirds feed on. These seabirds include different species of albatross, petrel, and shearwater, as well as the Australasian gannet and rockhopper penguin.
The Central Indo-Pacific realm includes the seas surrounding the northern half of Australia, Papua New Guinea, Solomon Islands, Vanuatu, New Caledonia, Fiji, and Tonga. This marine realm has the greatest diversity of tropical coral in the world and includes the world’s two largest coral formations: Australia’s Great Barrier Reef and the New Caledonia Barrier Reef. The Great Barrier Reef, a UNESCO World Heritage Site off the coast of northeast Australia, is 344,400 square kilometers (133,000 square miles).
Antarctica Physical Geography
The continent of Antarctica makes up most of the Antarctic region. The Antarctic is a cold, remote area in the Southern Hemisphere encompassed by the Antarctic Convergence. The Antarctic Convergence is an uneven line of latitude where cold, northward-flowing Antarctic waters meet the warmer waters of the world’s oceans. The Antarctic covers approximately 20 percent of the Southern Hemisphere.
Antarctica is the fifth-largest continent in terms of total area. (It is larger than both Oceania and Europe.) Antarctica is a unique continent in that it does not have a native population. There are no countries in Antarctica, although seven nations claim different parts of it: New Zealand, Australia, France, Norway, the United Kingdom, Chile, and Argentina.
The Antarctic Ice Sheet dominates the region. It is the largest single piece of ice on Earth. This ice sheet even extends beyond the continent when snow and ice are at their most extreme.
The ice surface dramatically grows in size from about 3 million square kilometers (1.2 million square miles) at the end of summer to about 19 million square kilometers (7.3 million square miles) by winter. Ice sheet growth mainly occurs at the coastal ice shelves, primarily the Ross Ice Shelf and the Ronne Ice Shelf. Ice shelves are floating sheets of ice that are connected to the continent. Glacial ice moves from the continent’s interior to these lower-elevation ice shelves at rates of 10 to 1,000 meters (33-32,808 feet) per year.
Antarctica has a number of mountain summits, including the Transantarctic Mountains, which divide the continent into eastern and western regions. A few of these summits reach altitudes of more than 4,500 meters (14,764 feet). The elevation of the Antarctic Ice Sheet itself is about 2,000 meters (6,562 feet) and reaches 4,000 meters (13,123 feet) above sea level near the center of the continent.
Without any ice, Antarctica would emerge as a giant peninsula and archipelago of mountainous islands, known as Lesser Antarctica, and a single large landmass about the size of Australia, known as Greater Antarctica. These regions have different geologies.
Greater Antarctica, or East Antarctica, is composed of older, igneous and metamorphic rocks. Lesser Antarctica, or West Antarctica, is made up of younger, volcanic and sedimentary rock. Lesser Antarctica, in fact, is part of the “Ring of Fire,” a tectonically active area around the Pacific Ocean. Tectonic activity is the interaction of plates on Earth’s crust, often resulting in earthquakes and volcanoes. Mount Erebus, located on Antarctica’s Ross Island, is the southernmost active volcano on Earth.
The majority of the islands and archipelagos of Lesser Antarctica are volcanic and heavily glaciated. They are also home to a number of high mountains.
The oceans surrounding Antarctica provide an important physical component of the Antarctic region. The waters surrounding Antarctica are relatively deep, reaching 4,000 to 5,000 meters (13,123 to 16,404 feet) in depth.
Antarctica has an extremely cold, dry climate. Winter temperatures along Antarctica’s coast generally range from -10° Celsius to -30° Celsius (14° Fahrenheit to -22° Fahrenheit). During the summer, coastal areas hover around 0°C (32°F) but can reach temperatures as high as 9°C (48°F).
In the mountainous, interior regions, temperatures are much colder, dropping below -60°C (-76°F) in winter and -20°C (-4°F) in summer. In 1983, Russia’s Vostok Research Station measured the coldest temperature ever recorded on Earth: -89.2°C (-128.6°F). An even lower temperature was measured using satellite data taken in 2010: -93.2°C (-135.8°F)
Precipitation in the Antarctic is hard to measure. It always falls as snow. Antarctica’s interior is believed to receive only 50 to 100 millimeters (2-4 inches) of water (in the form of snow) every year. The Antarctic desert is one of the driest deserts in the world.
The Antarctic region has an important role in global climate processes. It is an integral part of the Earth’s heat balance. The heat balance, also called the energy balance, is the relationship between the amount of solar heat absorbed by Earth’s atmosphere and the amount of heat reflected back into space.
Antarctica has a larger role than most continents in maintaining Earth’s heat balance. Ice is more reflective than land or water surfaces. The massive Antarctic Ice Sheet reflects a large amount of solar radiation away from Earth’s surface. As global ice cover (ice sheets and glaciers) decreases, the reflectivity of Earth’s surface also decreases. This allows more incoming solar radiation to be absorbed by the Earth’s surface, causing an unequal heat balance linked to global warming, the current period of climate change.
The waters surrounding Antarctica are a key part of the “ocean conveyor belt,” a global system in which water circulates around the globe based on density and on currents. The cold waters surrounding Antarctica, known as the Antarctic Bottom Water, are so dense that they push against the ocean floor. The Antarctic Bottom Water causes warmer waters to rise, or upwell.
Antarctic upwelling is so strong that it helps move water around the entire planet. This movement is aided by strong winds that circumnavigate Antarctica. Without the aid of the oceans around Antarctica, the Earth’s waters would not circulate in a balanced and efficient manner.
Lichens, mosses, and terrestrial algae are among the few species of vegetation that grow in Antarctica. More of this vegetation grows in the northern and coastal regions of Antarctica, while the interior has little if any vegetation.
The ocean, however, teems with fish and other marine life. In fact, the waters surrounding Antarctica are among the most diverse on the planet. Upwelling allows phytoplankton and algae to flourish. Thousands of species, such as krill, feed on the plankton. Fish and a large variety of marine mammals thrive in the cold Antarctic waters. Blue, fin, humpback, right, minke, sei, and sperm whales have healthy populations in Antarctica.