Europe is a continent located in the Northern Hemisphere and in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west and the Mediterranean Sea to the south, it comprises the westernmost part of Eurasia. Since around 1850, Europe is most considered to be separated from Asia by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas and the waterways of the Turkish Straits. Although the term "continent" implies physical geography, the land border is somewhat arbitrary and has been redefined several times since its first conception in classical antiquity; the division of Eurasia into two continents reflects East-West cultural and ethnic differences which vary on a spectrum rather than with a sharp dividing line. The geographic border does not follow political boundaries, with Turkey and Kazakhstan being transcontinental countries. A strict application of the Caucasus Mountains boundary places two comparatively small countries and Georgia, in both continents.
Europe covers 2 % of the Earth's surface. Politically, Europe is divided into about fifty sovereign states of which the Russian Federation is the largest and most populous, spanning 39% of the continent and comprising 15% of its population. Europe had a total population of about 741 million as of 2016; the European climate is affected by warm Atlantic currents that temper winters and summers on much of the continent at latitudes along which the climate in Asia and North America is severe. Further from the sea, seasonal differences are more noticeable than close to the coast. Europe, in particular ancient Greece, was the birthplace of Western civilization; the fall of the Western Roman Empire in 476 AD and the subsequent Migration Period marked the end of ancient history and the beginning of the Middle Ages. Renaissance humanism, exploration and science led to the modern era. Since the Age of Discovery started by Portugal and Spain, Europe played a predominant role in global affairs. Between the 16th and 20th centuries, European powers controlled at various times the Americas all of Africa and Oceania and the majority of Asia.
The Age of Enlightenment, the subsequent French Revolution and the Napoleonic Wars shaped the continent culturally and economically from the end of the 17th century until the first half of the 19th century. The Industrial Revolution, which began in Great Britain at the end of the 18th century, gave rise to radical economic and social change in Western Europe and the wider world. Both world wars took place for the most part in Europe, contributing to a decline in Western European dominance in world affairs by the mid-20th century as the Soviet Union and the United States took prominence. During the Cold War, Europe was divided along the Iron Curtain between NATO in the West and the Warsaw Pact in the East, until the revolutions of 1989 and fall of the Berlin Wall. In 1949 the Council of Europe was founded, following a speech by Sir Winston Churchill, with the idea of unifying Europe to achieve common goals, it includes all European states except for Belarus and Vatican City. Further European integration by some states led to the formation of the European Union, a separate political entity that lies between a confederation and a federation.
The EU originated in Western Europe but has been expanding eastward since the fall of the Soviet Union in 1991. The currency of most countries of the European Union, the euro, is the most used among Europeans. In classical Greek mythology, Europa was a Phoenician princess; the word Europe is derived from her name. The name contains the elements εὐρύς, "wide, broad" and ὤψ "eye, countenance", hence their composite Eurṓpē would mean "wide-gazing" or "broad of aspect". Broad has been an epithet of Earth herself in the reconstructed Proto-Indo-European religion and the poetry devoted to it. There have been attempts to connect Eurṓpē to a Semitic term for "west", this being either Akkadian erebu meaning "to go down, set" or Phoenician'ereb "evening, west", at the origin of Arabic Maghreb and Hebrew ma'arav. Michael A. Barry, professor in Princeton University's Near Eastern Studies Department, finds the mention of the word Ereb on an Assyrian stele with the meaning of "night, sunset", in opposition to Asu " sunrise", i.e. Asia.
The same naming motive according to "cartographic convention" appears in Greek Ἀνατολή. Martin Litchfield West stated that "phonologically, the match between Europa's name and any form of the Semitic word is poor." Next to these hypotheses there is a Proto-Indo-European root *h1regʷos, meaning "darkness", which produced Greek Erebus. Most major world languages use words derived from Europa to refer to the continent. Chinese, for example, uses the word Ōuzhōu. In some Turkic languages the Persian name Frangistan is used casually in referring to much of Europe, besides official names such as Avrupa or Evropa; the prevalent definition of Europe as a geographical term has been in use since the mid-19th century. Europe is taken to be bounded by large bodies of water
Cape Verde or Cabo Verde the Republic of Cabo Verde, is an island country spanning an archipelago of 10 volcanic islands in the central Atlantic Ocean. It forms part of the Macaronesia ecoregion, along with the Azores, Canary Islands and the Savage Isles. In ancient times these islands were referred to as "the Islands of the Blessed" or the "Fortunate Isles". Located 570 kilometres west of the Cape Verde Peninsula off the coast of Northwest Africa, the islands cover a combined area of over 4,000 square kilometres; the Cape Verde archipelago was uninhabited until the 15th century, when Portuguese explorers discovered and colonized the islands, establishing the first European settlement in the tropics. Ideally located for the Atlantic slave trade, the islands grew prosperous throughout the 16th and 17th centuries, attracting merchants and pirates; the end of slavery in the 19th century led to economic emigration. Cape Verde recovered as an important commercial center and stopover for shipping routes.
Incorporated as an overseas department of Portugal in 1951, the islands continued to campaign for independence, peacefully achieved in 1975. Since the early 1990s, Cape Verde has been a stable representative democracy, remains one of the most developed and democratic countries in Africa. Lacking natural resources, its developing economy is service-oriented, with a growing focus on tourism and foreign investment, its population of around 540,000 is of mixed European, Moorish and African heritage, predominantly Roman Catholic, reflecting the legacy of Portuguese rule. A sizeable diaspora community exists across the world outnumbering inhabitants on the islands; the name "Cape Verde" has been used in English for the archipelago and, since independence in 1975, for the country. In 2013, the Cape Verdean government determined that the Portuguese designation Cabo Verde would henceforth be used for official purposes, such as at the United Nations in English contexts. Cape Verde is a member of the African Union.
The name of the country stems on the Senegalese coast. In 1444, Portuguese explorers had named that landmark as Cabo Verde, a few years before they discovered the islands. On 24 October 2013, the country's delegation announced at the United Nations that the official name should no longer be translated into other languages. Instead of "Cape Verde", the designation "Republic of Cabo Verde" is to be used. Before the arrival of Europeans, the Cape Verde Islands were uninhabited; the islands of the Cape Verde archipelago were discovered by Genoese and Portuguese navigators around 1456. According to Portuguese official records, the first discoveries were made by Genoa-born António de Noli, afterwards appointed governor of Cape Verde by Portuguese King Afonso V. Other navigators mentioned as contributing to discoveries in the Cape Verde archipelago are Diogo Gomes, Diogo Dias, Diogo Afonso and the Italian Alvise Cadamosto. In 1462, Portuguese settlers arrived at Santiago and founded a settlement they called Ribeira Grande.
Ribeira Grande was the first permanent European settlement in the tropics. In the 16th century, the archipelago prospered from the Atlantic slave trade. Pirates attacked the Portuguese settlements. Francis Drake, an English privateer, twice sacked the capital Ribeira Grande in 1585 when it was a part of the Iberian Union. After a French attack in 1712, the town declined in importance relative to nearby Praia, which became the capital in 1770. Decline in the slave trade in the 19th century resulted in an economic crisis. Cape Verde's early prosperity vanished. However, the islands' position astride mid-Atlantic shipping lanes made Cape Verde an ideal location for re-supplying ships; because of its excellent harbour, the city of Mindelo, located on the island of São Vicente, became an important commercial centre during the 19th century. Diplomat Edmund Roberts visited Cape Verde in 1832. With few natural resources and inadequate sustainable investment from the Portuguese, the citizens grew discontented with the colonial masters, who refused to provide the local authorities with more autonomy.
In 1951, Portugal changed Cape Verde's status from a colony to an overseas province in an attempt to blunt growing nationalism. In 1956, Amílcar Cabral and a group of fellow Cape Verdeans and Guineans organised the clandestine African Party for the Independence of Guinea and Cape Verde, it demanded improvement in economic and political conditions in Cape Verde and Portuguese Guinea and formed the basis of the two nations' independence movement. Moving its headquarters to Conakry, Guinea in 1960, the PAIGC began an armed rebellion against Portugal in 1961. Acts of sabotage grew into a war in Portuguese Guinea that pitted 10,000 Soviet Bloc-supported PAIGC soldiers against 35,000 Portuguese and African troops. By 1972, the PAIGC controlled much of Portuguese Guinea despite the presence of the Portuguese troops, but the organization did not attempt to disrupt Portuguese control in Cape Verde. Portuguese Guinea declared independence in 1973 and was granted de jure independence in 1974. A budding independence movement — led by Amílcar Cabral, assassinated in 1973 — passed on to his half-brother Luís Cabral and culminated in independence for the archipelago in
Lanzarote is a Spanish island, the northernmost and easternmost of the autonomous Canary Islands in the Atlantic Ocean. It is located 125 kilometres off the north coast of Africa and 1,000 kilometres from the Iberian Peninsula. Covering 845.94 square kilometres, Lanzarote is the fourth-largest of the islands in the archipelago. With 149,183 inhabitants, it is the third most populous Canary Island, after Tenerife and Gran Canaria. Located in the centre-west of the island is Timanfaya National Park, one of its main attractions; the island was declared a biosphere reserve by UNESCO in 1993. The island's capital is Arrecife; the first recorded name for the island, given by Italian-Majorcan cartographer Angelino Dulcert, was Insula de Lanzarotus Marocelus, after the Genoese navigator Lancelotto Malocello, from which the modern name is derived. The island's name in the native language was Tyterogaka or Tytheroygaka, which may mean "one, all ochre". Lanzarote is located 11 kilometres north-east of Fuerteventura and just over 1 kilometre from Graciosa.
The dimensions of the island are 60 kilometres from north to south and 25 kilometres from west to east. Lanzarote has 213 kilometres of coastline, of which 10 kilometres are sand, 16.5 kilometres are beach, the remainder is rocky. Its landscape includes the mountain ranges of Famara in Ajaches to the south. South of the Famara massif is the El Jable desert, which separates Montañas del Fuego; the highest peak is Peñas del Chache. The "Tunnel of Atlantis", the largest underwater volcanic tunnel in the world, is part of the Cueva de los Verdes lava tube. Called the "Island of Eternal Spring", Lanzarote has a subtropical-desert climate according to the Köppen climatic classification; the small amount of precipitation is concentrated in the winter. Rainfall during summer is a rare phenomenon and several summers are dry without any precipitation. On average the island receives 16 days of precipitation between December and February. Sometimes, the hot sirocco wind prevails, causing dusty conditions across the island.
Average precipitation in June and August is less than 0.5 millimetres. It borders on a tropical climate, with winter means of 18 °C and summer means of 25 °C. Lanzarote is the northernmost and easternmost island of the Canary Islands and has a volcanic origin, it was born through fiery eruptions and has solidified lava streams as well as extravagant rock formations. The island emerged about 15 million years ago as product of the Canary hotspot; the island, along with others, emerged after the breakup of the African and the American continental plates. The greatest recorded eruptions occurred between 1730 and 1736 in the area now designated Timanfaya National Park; as of 2018, 149,183 people live on Lanzarote, an increase of 9.4% from 2006. The seat of the island government is in the capital, which has a population of 59,000. According to the census of 2006, the majority of the inhabitants are Spanish with a sizeable number of residents from other nations, notably Colombians, Moroccans and Irish.
Other populous groups include Chinese people and Indians, which constitute a large proportion of the remaining 15.6% of the population. The island has an international airport, Arrecife Airport, through which 5,438,178 passengers travelled in 2008. Tourism has been the mainstay of the island's economy for over 40 years, the only other industry being agriculture. Lanzarote is part of the province of Las Palmas, is divided into seven municipalities: Arrecife Haría San Bartolomé Teguise Tías Tinajo Yaiza There are five hundred different kinds of plants on the island, of which 17 species are endemic; these plants have adapted to the relative scarcity of water in the same way as succulents. They include the Canary Island date palm, found in damper areas of the north, the Canary Island pine and wild olive trees. Laurisilva trees, which once covered the highest parts of Risco de Famara, are found today. After winter rainfall, the vegetation comes to a colourful bloom between March; the vineyards of La Gería, Lanzarote DO wine region, are a protected area.
Single vines are planted in pits 4–5 metres wide and 2–3 metres deep, with small stone walls around each pit. This agricultural technique is designed to harvest rainfall and overnight dew and to protect the plants from the winds. There are 180 different species of lichen-forming fungi; these survive in the suitable areas like rock surfaces, promote weathering. Apart from the native bats and the mammals which accompanied humans to the island, there are few vertebrate species on Lanzarote; these include reptiles. Some interesting endemic animals are the Gallotia lizards and the blind Munidopsis polymorpha crabs found in the Jameos del Agua lagoon, formed by a volcanic eruption; the island is home to one of two surviving populations of the threatened Canarian Egyptian vulture. The official natural symbols associated with Lanzarote are Munidopsis polymorpha and Euphorbi
Maras is a town in the Sacred Valley of the Incas, 40 kilometers north of Cuzco, in the Cuzco Region of Peru. The town is well known for its salt evaporation ponds, located towards Urubamba from the town center, which have been in use since Inca times; the salt-evaporation ponds are four kilometers north of the town, down a canyon that descends to the Rio Vilcanota and the Sacred Valley of the Incas. The Maras area is accessible by a paved road, which leads from the main road leading through the Sacred Valley between Cuzco and the surrounding towns. Tourist sites in the area include the colonial church, the nearby Moray Inca ruins, the local salt evaporation ponds, the surrounding scenery. Since pre-Inca times, salt has been obtained in Maras by evaporating salty water from a local subterranean stream; the salty water emerges at a spring, a natural outlet of the underground stream. The flow is directed into an intricate system of tiny channels constructed so that the water runs down onto the several hundred ancient terraced ponds.
All the ponds are less than four meters square in area, none exceeds thirty centimeters in depth. All are shaped into polygons with the flow of water controlled and monitored by the workers; the altitude of the ponds decreases, so that the water may flow through the myriad branches of the water-supply channels and be introduced through a notch in one sidewall of each pond. The proper maintenance of the adjacent feeder channel, the side walls and the water-entry notch, the pond's bottom surface, the quantity of water, the removal of accumulated salt deposits requires close cooperation among the community of users, it is agreed among local residents and pond workers that the cooperative system was established during the time of the Incas, if not earlier. As water evaporates from the sun-warmed ponds, the water becomes supersaturated and salt precipitates as various size crystals onto the inner surfaces of a pond's earthen walls and on the pond's earthen floor; the pond's keeper closes the water-feeder notch and allows the pond to go dry.
Within a few days the keeper scrapes the dry salt from the sides and bottom, puts it into a suitable vessel, reopens the water-supply notch, carries away the salt. Color of the salt varies from white to a light reddish or brownish tan, depending on the skill of an individual worker; some salt is sold at a gift store nearby. The salt mines traditionally have been available to any person wishing to harvest salt; the owners of the salt ponds must be members of the community, families that are new to the community wishing to propitiate a salt pond get the one farthest from the community. The size of the salt pond assigned to a family depends on the family's size. There are many unused salt pools available to be farmed. Any prospective salt farmer need only locate an empty unmaintained pond, consult with the local informal cooperative, learn how to keep a pond properly within the accepted communal system, start working. Antonio Sinchi Roca Inka, 17th-century Quechua painter Maras, National Geographic
Salt is a mineral composed of sodium chloride, a chemical compound belonging to the larger class of salts. Salt is present in vast quantities in seawater; the open ocean has about 35 grams of solids per liter of sea water, a salinity of 3.5%. Salt is essential for life in general, saltiness is one of the basic human tastes. Salt is one of the oldest and most ubiquitous food seasonings, salting is an important method of food preservation; some of the earliest evidence of salt processing dates to around 6,000 BC, when people living in the area of present-day Romania boiled spring water to extract salts. Salt was prized by the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites and the Indians. Salt became an important article of trade and was transported by boat across the Mediterranean Sea, along specially built salt roads, across the Sahara on camel caravans; the scarcity and universal need for salt have led nations to go to war over it and use it to raise tax revenues. Salt has other cultural and traditional significance.
Salt is processed from salt mines, by the evaporation of seawater and mineral-rich spring water in shallow pools. Its major industrial products are caustic chlorine. Of the annual global production of around two hundred million tonnes of salt, about 6% is used for human consumption. Other uses include water conditioning processes, de-icing highways, agricultural use. Edible salt is sold in forms such as sea salt and table salt which contains an anti-caking agent and may be iodised to prevent iodine deficiency; as well as its use in cooking and at the table, salt is present in many processed foods. Sodium is an essential nutrient for human health via its role as an osmotic solute. Excessive salt consumption may increase the risk of cardiovascular diseases, such as hypertension, in children and adults; such health effects of salt have long been studied. Accordingly, numerous world health associations and experts in developed countries recommend reducing consumption of popular salty foods; the World Health Organization recommends that adults should consume less than 2,000 mg of sodium, equivalent to 5 grams of salt per day.
All through history, the availability of salt has been pivotal to civilization. What is now thought to have been the first city in Europe is Solnitsata, in Bulgaria, a salt mine, providing the area now known as the Balkans with salt since 5400 BC; the name Solnitsata means "salt works". While people have used canning and artificial refrigeration to preserve food for the last hundred years or so, salt has been the best-known food preservative for meat, for many thousands of years. A ancient salt-works operation has been discovered at the Poiana Slatinei archaeological site next to a salt spring in Lunca, Neamț County, Romania. Evidence indicates that Neolithic people of the Precucuteni Culture were boiling the salt-laden spring water through the process of briquetage to extract the salt as far back as 6050 BC; the salt extracted from this operation may have had a direct correlation to the rapid growth of this society's population soon after its initial production began. The harvest of salt from the surface of Xiechi Lake near Yuncheng in Shanxi, dates back to at least 6000 BC, making it one of the oldest verifiable saltworks.
There is more salt in animal tissues, such as meat and milk, than in plant tissues. Nomads who subsist on their flocks and herds do not eat salt with their food, but agriculturalists, feeding on cereals and vegetable matter, need to supplement their diet with salt. With the spread of civilization, salt became one of the world's main trading commodities, it was of high value to the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites and other peoples of antiquity. In the Middle East, salt was used to ceremonially seal an agreement, the ancient Hebrews made a "covenant of salt" with God and sprinkled salt on their offerings to show their trust in him. An ancient practice in time of war was salting the earth: scattering salt around in a defeated city to prevent plant growth; the Bible tells the story of King Abimelech, ordered by God to do this at Shechem, various texts claim that the Roman general Scipio Aemilianus Africanus ploughed over and sowed the city of Carthage with salt after it was defeated in the Third Punic War.
Salt may have been used for barter in connection with the obsidian trade in Anatolia in the Neolithic Era. Salt was included among funeral offerings found in ancient Egyptian tombs from the third millennium BC, as were salted birds, salt fish. From about 2800 BC, the Egyptians began exporting salt fish to the Phoenicians in return for Lebanon cedar and the dye Tyrian purple. Herodotus described salt trading routes across Libya back in the 5th century BC. In the early years of the Roman Empire, roads were built for the transportation of salt from the salt imported at Ostia to the capital. In Africa, salt was used as currency south of the Sahara, slabs of rock salt were used as coins in Abyssinia. Moorish merchants in the 6th century traded salt for weight for weight; the Tuareg have traditionally maintained routes across the Sahara for the transportation of salt by Azalai. The caravans
The Atacama Desert is a desert plateau in South America covering a 1000-km strip of land on the Pacific coast, west of the Andes mountains. The Atacama desert is one of the driest places in the world, as well as the only true desert to receive less precipitation than the polar deserts. According to estimates, the Atacama Desert occupies 105,000 km2, or 128,000 km2 if the barren lower slopes of the Andes are included. Most of the desert is composed of stony terrain, salt lakes and felsic lava that flows towards the Andes; the desert owes its extreme aridity to a constant temperature inversion due to the cool north-flowing Humboldt ocean current, to the presence of the strong Pacific anticyclone. The most arid region of the Atacama desert is situated between two mountain chains of sufficient height to prevent moisture advection from either the Pacific or the Atlantic Oceans, a two-sided rain shadow. According to the World Wide Fund for Nature, the Atacama Desert ecoregion occupies a continuous strip for nearly 1,600 km along the narrow coast of the northern third of Chile, from near Arica southward to near La Serena.
The National Geographic Society considers the coastal area of southern Peru to be part of the Atacama Desert and includes the deserts south of the Ica Region in Peru. Peru borders it on the north and the Chilean Matorral ecoregion borders it on the south. To the east lies the less arid Central Andean dry puna ecoregion; the drier portion of this ecoregion is located south of the Loa River between the parallel Sierra Vicuña Mackenna and Cordillera Domeyko. To the north of the Loa lies the Pampa del Tamarugal; the Coastal Cliff of northern Chile west of the Chilean Coast Range is the main topographical feature of the coast. The geomorphology of the Atacama Desert has been characterized as a low-relief bench "similar to a giant uplifted terrace" by Armijo and co-workers; the intermediate depression forms a series of endorheic basins in much of Atacama Desert south of latitude 19°30'S. North of this latitude, the intermediate depression drains into the Pacific Ocean. Although the total lack of precipitation is the most prominent characteristic of the Atacama Desert, exceptions may occur.
In July 2011, an extreme Antarctic cold front broke through the rain shadow, bringing 80 cm of snow to the plateau, stranding residents across the region in Bolivia, where many drivers became stuck in snow drifts and emergency crews became overtaxed with a large number of rescue calls. In 2012, the altiplano winter brought floods to San Pedro de Atacama. On 25 March 2015, heavy rainfall affected the southern part of the Atacama Desert. Resulting floods triggered mudflows that affected the cities of Copiapo, Tierra Amarilla and Diego de Almagro, causing the deaths of more than 100 people; the Atacama Desert is known as the driest nonpolar place in the world the surroundings of the abandoned Yungay town. The average rainfall is about 15 mm per year, although some locations, such as Arica and Iquique, receive 1 to 3 mm in a year. Moreover, some weather stations in the Atacama have never received rain. Periods up to four years have been registered with no rainfall in the central sector, delimited by the cities of Antofagasta and Copiapó, in Chile.
Evidence suggests that the Atacama may not have had any significant rainfall from 1570 to 1971. The Atacama Desert may be the oldest desert on earth, has experienced extreme hyperaridity for at least 3 million years, making it the oldest continuously arid region on earth; the long history of aridity raises the possibility that supergene mineralisation, under the appropriate conditions, can form in arid environments, instead of requiring humid conditions. The presence of evaporite formations suggest that in some sections of the Atacama Desert, arid conditions have persisted for the last 200 million years; the Atacama is so arid that many mountains higher than 6,000 m are free of glaciers. Only the highest peaks have some permanent snow coverage; the southern part of the desert, between 25 and 27°S, may have been glacier-free throughout the Quaternary, though permafrost extends down to an altitude of 4,400 m and is continuous above 5,600 m. Studies by a group of British scientists have suggested that some river beds have been dry for 120,000 years.
However, some locations in the Atacama receive a marine fog known locally as the camanchaca, providing sufficient moisture for hypolithic algae and some cacti—the genus Copiapoa is notable among these. Geographically, the aridity of the Atacama is explained by it being situated between two mountain chains of sufficient height to prevent moisture advection from either the Pacific or the Atlantic Oceans, a two-sided rain shadow. In a region about 100 km south of Antofagasta, which averages 3,000 m in elevation, the soil has been compared to that of Mars. Owing to its otherworldly appearance, the Atacama has been used as a location for filming Mars scenes, most notably in the television series Space Odyssey: Voyage to the Planets. In 2003, a team of researchers published a report in which they duplicated the tests used by the Viking 1 and Viking 2 Mars landers to detect life, were unable to detect any signs in Atacama Desert soil in the region of Yungay; the region may be unique on Earth in this regard, is being used by NASA to test instru
San Francisco Bay
San Francisco Bay is a shallow estuary in the US state of California. It is surrounded by a contiguous region known as the San Francisco Bay Area, is dominated by the large cities of San Jose, San Francisco and Oakland. San Francisco Bay drains water from 40 percent of California. Water from the Sacramento and San Joaquin rivers, from the Sierra Nevada mountains, flow into Suisun Bay, which travels through the Carquinez Strait to meet with the Napa River at the entrance to San Pablo Bay, which connects at its south end to San Francisco Bay; the Guadalupe River enters the bay at its southernmost point in San Jose. The Guadalupe drains water from the Santa Cruz mountains and Hamilton Mountain ranges in southernmost San Jose, it enters the bay at the town of Alviso. It connects to the Pacific Ocean via the Golden Gate strait. However, this entire group of interconnected bays is called the San Francisco Bay; the bay was designated a Ramsar Wetland of International Importance on February 2, 2012. The bay covers somewhere between 400 and 1,600 square miles, depending on which sub-bays, wetlands, so on are included in the measurement.
The main part of the bay measures three to twelve miles wide east-to-west and somewhere between 48 miles 1 and 60 miles 2 north-to-south. It is the largest Pacific estuary in the Americas; the bay was navigable as far south as San Jose until the 1850s, when hydraulic mining released massive amounts of sediment from the rivers that settled in those parts of the bay that had little or no current. Wetlands and inlets were deliberately filled in, reducing the Bay's size since the mid-19th century by as much as one third. Large areas of wetlands have been restored, further confusing the issue of the Bay's size. Despite its value as a waterway and harbor, many thousands of acres of marshy wetlands at the edges of the bay were, for many years, considered wasted space; as a result, soil excavated for building projects or dredged from channels was dumped onto the wetlands and other parts of the bay as landfill. From the mid-19th century through the late 20th century, more than a third of the original bay was filled and built on.
The deep, damp soil in these areas is subject to soil liquefaction during earthquakes, most of the major damage close to the Bay in the Loma Prieta earthquake of 1989 occurred to structures on these areas. The Marina District of San Francisco, hard hit by the 1989 earthquake, was built on fill, placed there for the Panama-Pacific International Exposition, although liquefaction did not occur on a large scale. In the 1990s, San Francisco International Airport proposed filling in hundreds more acres to extend its overcrowded international runways in exchange for purchasing other parts of the bay and converting them back to wetlands; the idea was, remains, controversial. There are five large islands in San Francisco Bay. Alameda, the largest island, was created when a shipping lane was cut to form the Port of Oakland in 1901, it is now a suburban community. Angel Island was known as "Ellis Island West" because it served as the entry point for immigrants from East Asia, it is now a state park accessible by ferry.
Mountainous Yerba Buena Island is pierced by a tunnel linking the east and west spans of the San Francisco–Oakland Bay Bridge. Attached to the north is the artificial and flat Treasure Island, site of the 1939 Golden Gate International Exposition. From the Second World War until the 1990s, both islands served as military bases and are now being redeveloped. Isolated in the center of the Bay is Alcatraz, the site of the famous federal penitentiary; the federal prison on Alcatraz Island no longer functions, but the complex is a popular tourist site. Despite its name, Mare Island in the northern part of the bay is a peninsula rather than an island. San Francisco Bay is thought to represent a down-warping of the Earth's crust between the San Andreas Fault to the west and the Hayward Fault to the east, though the precise nature of this remains under study. About 560,000 years ago, a tectonic shift caused the large inland Lake Corcoran to spill out the central valley and through the Carquinez Strait, carving out sediment and forming canyons in what is now the northern part of the San Francisco Bay and Golden Gate strait.
Until the last ice age, the basin, now filled by the San Francisco Bay was a large linear valley with small hills, similar to most of the valleys of the Coast Ranges. As the great ice sheets began to melt, around 11,000 years ago, the sea level started to rise. By 5000 BC the sea level rose 300 feet; the valley become a bay, the small hills became islands. From 15,000 – 10,000 years ago, the Ohlone tribe inhabited the area, now the San Francisco Bay; the natives were displaced 5,000 years ago as the bay filled with water due to the rising sea level at the end of the ice age. The first European to see San Francisco Bay is N. de Morena, left at New Albion at Drakes Bay in Marin County, California by Sir Francis Drake in 1579 and walked to Mexico. The first recorded European discovery of San Francisco Bay was on November 4, 1769 when Spanish explorer Gaspar de Portolà, unable to find the port of Monterey, continued north close to what is now Pacifica and reached the summit of the 1,200-foot-high Sweeney Ridge, now marked as the place where he first sighted San Francisco Bay.
Portolá and his party did not realize what they had discovered, thinking they had arrived at a large arm of what is now called Drakes Bay. At the time, Drakes Bay went by the name Bahia de San