Radiocarbon dating
Radiocarbon dating is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was developed in the late 1940s by Willard Libby, who received the Nobel Prize in Chemistry for his work in 1960, it is based on the fact that radiocarbon is being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting 14C combines with atmospheric oxygen to form radioactive carbon dioxide, incorporated into plants by photosynthesis; when the animal or plant dies, it stops exchanging carbon with its environment, from that point onwards the amount of 14C it contains begins to decrease as the 14C undergoes radioactive decay. Measuring the amount of 14C in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died; the older a sample is, the less 14C there is to be detected, because the half-life of 14C is about 5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods permit accurate analysis of older samples.
Research has been ongoing since the 1960s to determine what the proportion of 14C in the atmosphere has been over the past fifty thousand years. The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age. Other corrections must be made to account for the proportion of 14C in different types of organisms, the varying levels of 14C throughout the biosphere. Additional complications come from the burning of fossil fuels such as coal and oil, from the above-ground nuclear tests done in the 1950s and 1960s; because the time it takes to convert biological materials to fossil fuels is longer than the time it takes for its 14C to decay below detectable levels, fossil fuels contain no 14C, as a result there was a noticeable drop in the proportion of 14C in the atmosphere beginning in the late 19th century. Conversely, nuclear testing increased the amount of 14C in the atmosphere, which attained a maximum in about 1965 of twice what it had been before the testing began.
Measurement of radiocarbon was done by beta-counting devices, which counted the amount of beta radiation emitted by decaying 14C atoms in a sample. More accelerator mass spectrometry has become the method of choice; the development of radiocarbon dating has had a profound impact on archaeology. In addition to permitting more accurate dating within archaeological sites than previous methods, it allows comparison of dates of events across great distances. Histories of archaeology refer to its impact as the "radiocarbon revolution". Radiocarbon dating has allowed key transitions in prehistory to be dated, such as the end of the last ice age, the beginning of the Neolithic and Bronze Age in different regions. In 1939, Martin Kamen and Samuel Ruben of the Radiation Laboratory at Berkeley began experiments to determine if any of the elements common in organic matter had isotopes with half-lives long enough to be of value in biomedical research, they synthesized 14C using the laboratory's cyclotron accelerator and soon discovered that the atom's half-life was far longer than had been thought.
This was followed by a prediction by Serge A. Korff employed at the Franklin Institute in Philadelphia, that the interaction of thermal neutrons with 14N in the upper atmosphere would create 14C, it had been thought that 14C would be more to be created by deuterons interacting with 13C. At some time during World War II, Willard Libby, at Berkeley, learned of Korff's research and conceived the idea that it might be possible to use radiocarbon for dating. In 1945, Libby moved to the University of Chicago, he published a paper in 1946 in which he proposed that the carbon in living matter might include 14C as well as non-radioactive carbon. Libby and several collaborators proceeded to experiment with methane collected from sewage works in Baltimore, after isotopically enriching their samples they were able to demonstrate that they contained 14C. By contrast, methane created from petroleum showed no radiocarbon activity because of its age; the results were summarized in a paper in Science in 1947, in which the authors commented that their results implied it would be possible to date materials containing carbon of organic origin.
Libby and James Arnold proceeded to test the radiocarbon dating theory by analyzing samples with known ages. For example, two samples taken from the tombs of two Egyptian kings and Sneferu, independently dated to 2625 BC plus or minus 75 years, were dated by radiocarbon measurement to an average of 2800 BC plus or minus 250 years; these results were published in Science in 1949. Within 11 years of their announcement, more than 20 radiocarbon dating laboratories had been set up worldwide. In 1960, Libby was awarded the Nobel Prize in Chemistry for this work. In nature, carbon exists as two stable, nonradioactive isotopes: carbon-12, carbon-13, a radioactive isotope, carbon-14 known as "radiocarbon"; the half-life
Adansonia digitata
Adansonia digitata, the baobab, is the most widespread tree species of the genus Adansonia, the baobabs, is native to the African continent. The long-lived pachycauls are found in dry, hot savannahs of sub-Saharan Africa, where they dominate the landscape, reveal the presence of a watercourse from afar, their growth rate is determined by ground water or rainfall, their maximum age, subject to much conjecture, seems to be in the order of 1,500 years. They have traditionally been valued as sources of food, health remedies or places of shelter and are steeped in legend and superstition. European explorers of old were inclined to carve their names on baobabs, many are defaced by modern graffiti. Common names for the baobab include dead-rat tree, monkey-bread tree, upside-down tree and cream of tartar tree; the vernacular name "baobab" is derived from Arabic بو حِباب, which means "father of many seeds". The scientific name Adansonia refers to the French explorer and botanist, Michel Adanson, who observed a specimen in 1749 on the island of Sor, Senegal.
On the nearby Îles des Madeleines Adanson found another baobab, 3.8 m in diameter, which bore the carvings of passing mariners on its trunk, including those of Henry the Navigator in 1444 and André Thevet in 1555. When Théodore Monod searched the island in the 20th century, the tree was not to be found however. Adanson concluded that the baobab, of all the trees he studied, “is the most useful tree in all.” He consumed baobab juice twice a day. He remained convinced. "Digitata" refers to the digits of the hand. The baobab's compound leaves with five leaflets are akin to a hand; the trees grow as solitary individuals, are large and distinctive elements of savannah or scrubland vegetation. Some large individuals live to well over a thousand years of age. All baobab trees are deciduous, losing their leaves in the dry season, remain leafless for nine months of the year, they can grow to between 5–25 m in height. They are in fact known both for trunk's girth; the trunk can reach a diameter of 10 -- 14 m.
The span of the roots exceed the tree's height, a factor that enables it to survive in a dry climate. Many consider the tree to be “upside-down” due to the trunk likeness to a taproot and the branches akin to finer capillary roots; the trunk can range from being reddish brown to grey. The bark can feel cork-like; the branches are thick and wide and stout compared to the trunk. During the early summer the tree bears large, white flowers; these are open during the late afternoon to stay open for one night. The pendulous, showy flowers have a large number of stamens, they have a sweet scent but emit a carrion smell when they turn brown and fall after 24 hours. Researchers have shown that they appear to be pollinated by fruit bats of the subfamily Pteropodinae; the flowers have 5 petals that are hairy on the inside. The sepals are 5-cleft; the stamens are divided into multiple anthers and styles are 7-10 rayed. The indehiscent fruit are large, egg-shaped capsules, they are filled with pulp that dries and falls to pieces which look like chunks of powdery, dry bread.
The seed are hard and kidney-shaped. The northern limit of its distribution in Africa is associated with rainfall patterns. On the Atlantic coast, this may be due to spreading after cultivation, its occurrence is limited in Central Africa, it is found only in the north of South Africa. In Eastern Africa, the trees grow in shrublands and on the coast. In Angola and Namibia, the baobabs grow in woodlands, in coastal regions, in addition to savannahs, it is found in Dhofar region of Oman and Yemen in the Arabian Peninsula, Western Asia. This tree is found in India in the dry regions of the country, in Penang, along certain streets; the baobab is native to most of Africa in drier, less tropical climates. It is not found in areas, it is sensitive to frost. More specifically: Mauritania, Guinea, Sierra Leone, Burkina Faso, Togo, Niger, Nigeria, n-Cameroon, Sudan, Congo, DR Congo, Ethiopia, s-Somalia, Tanzania, Zimbabwe, Mozambique, Angola, São Tomé, Príncipe isl. Annobon isl. Java, Sri Lanka, Jamaica, South Africa, Botswana, Puerto Rico, Dominican Republic, Seychelles, Comores, India, sw-Yemen, China, Fujian, Yunnan.
Adansonia trees produce faint growth rings annually, but they are not reliable for aging specimens, because they are difficult to count and may fade away as the wood ages. Radiocarbon dating has provided data on a few individuals of A. digitata. The Panke baobab in Zimbabwe was some 2,450 years old when it died in 2011, making it the oldest angiosperm documented, two other trees — Dorslandboom in Namibia and Glencoe in South Africa — were estimated to be 2,000 years old. Another specimen known as Grootboom was dat
Plant
Plants are multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae. Plants were treated as one of two kingdoms including all living things that were not animals, all algae and fungi were treated as plants. However, all current definitions of Plantae exclude the fungi and some algae, as well as the prokaryotes. By one definition, plants form the clade Viridiplantae, a group that includes the flowering plants and other gymnosperms and their allies, liverworts and the green algae, but excludes the red and brown algae. Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplasts that are derived from endosymbiosis with cyanobacteria, their chloroplasts contain b, which gives them their green color. Some plants are parasitic or mycotrophic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is common.
There are about 320 thousand species of plants, of which the great majority, some 260–290 thousand, are seed plants. Green plants provide a substantial proportion of the world's molecular oxygen and are the basis of most of Earth's ecosystems on land. Plants that produce grain and vegetables form humankind's basic foods, have been domesticated for millennia. Plants have many cultural and other uses, as ornaments, building materials, writing material and, in great variety, they have been the source of medicines and psychoactive drugs; the scientific study of plants is known as a branch of biology. All living things were traditionally placed into one of two groups and animals; this classification may date from Aristotle, who made the distincton between plants, which do not move, animals, which are mobile to catch their food. Much when Linnaeus created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia and Animalia. Since it has become clear that the plant kingdom as defined included several unrelated groups, the fungi and several groups of algae were removed to new kingdoms.
However, these organisms are still considered plants in popular contexts. The term "plant" implies the possession of the following traits multicellularity, possession of cell walls containing cellulose and the ability to carry out photosynthesis with primary chloroplasts; when the name Plantae or plant is applied to a specific group of organisms or taxon, it refers to one of four concepts. From least to most inclusive, these four groupings are: Another way of looking at the relationships between the different groups that have been called "plants" is through a cladogram, which shows their evolutionary relationships; these are not yet settled, but one accepted relationship between the three groups described above is shown below. Those which have been called "plants" are in bold; the way in which the groups of green algae are combined and named varies between authors. Algae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom.
The seaweeds range from large multicellular algae to single-celled organisms and are classified into three groups, the green algae, red algae and brown algae. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, they are no longer classified as plants as defined here; the Viridiplantae, the green plants – green algae and land plants – form a clade, a group consisting of all the descendants of a common ancestor. With a few exceptions, the green plants have the following features in common, they undergo closed mitosis without centrioles, have mitochondria with flat cristae. The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria. Two additional groups, the Rhodophyta and Glaucophyta have primary chloroplasts that appear to be derived directly from endosymbiotic cyanobacteria, although they differ from Viridiplantae in the pigments which are used in photosynthesis and so are different in colour.
These groups differ from green plants in that the storage polysaccharide is floridean starch and is stored in the cytoplasm rather than in the plastids. They appear to have had a common origin with Viridiplantae and the three groups form the clade Archaeplastida, whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event; this is the broadest modern definition of the term'plant'. In contrast, most other algae not only have different pigments but have chloroplasts with three or four surrounding membranes, they are not close relatives of the Archaeplastida having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in the broadest modern definition of the plant kingdom, although they were in the past; the green plants or Viridiplantae were traditionally divided into the green algae (including
Tanzania
Tanzania the United Republic of Tanzania, is a country in eastern Africa within the African Great Lakes region. It borders Uganda to the north. Mount Kilimanjaro, Africa's highest mountain, is in north-eastern Tanzania; the first humans known lived in Pliocene Tanzania 6 million years ago. The genus Australopithecus ranged all over Africa 4-2 million years ago. Following the rise of Homo erectus 1.8 million years ago, mankind spread all over the Old World, in the New World and Australia under the species Homo sapiens. Homo sapiens overtook Africa and absorbed the older archaic species and subspecies of humanity. One of the oldest known ethnic groups still existing, the Hadzabe, appears to have originated in Tanzania, their oral history recalls ancestors who were tall and were the first to use fire and lived in caves, much like Homo erectus or Homo heidelbergensis who lived in the same region before them. In the Stone and Bronze Age, prehistoric migrations into Tanzania included Southern Cushitic speakers who moved south from present-day Ethiopia.
These movements took place at about the same time as the settlement of the Mashariki Bantu from West Africa in the Lake Victoria and Lake Tanganyika areas. They subsequently migrated across the rest of Tanzania between 1,700 years ago. European colonialism began in mainland Tanzania during the late 19th century when Germany formed German East Africa, which gave way to British rule following World War I; the mainland was governed as Tanganyika, with the Zanzibar Archipelago remaining a separate colonial jurisdiction. Following their respective independence in 1961 and 1963, the two entities merged in April 1964 to form the United Republic of Tanzania; the United Nations estimated Tanzania's 2016 population at 55.57 million. The population is composed of several ethnic and religious groups; the sovereign state of Tanzania is a presidential constitutional republic and since 1996 its official capital city has been Dodoma where the president's office, the National Assembly, some government ministries are located.
Dar es Salaam, the former capital, retains most government offices and is the country's largest city, principal port, leading commercial centre. Tanzania is a de facto one-party state with the democratic socialist Chama Cha Mapinduzi party in power. Tanzania is densely forested in the north-east, where Mount Kilimanjaro is located. Three of Africa's Great Lakes are within Tanzania. To the north and west lie Lake Victoria, Africa's largest lake, Lake Tanganyika, the continent's deepest lake, known for its unique species of fish. To the south lies Lake Malawi; the eastern shore is humid, with the Zanzibar Archipelago just offshore. The Menai Bay Conservation Area is Zanzibar's largest marine protected area; the Kalambo Falls, located on the Kalambo River at the Zambian border, is the second highest uninterrupted waterfall in Africa. Over 100 different languages are spoken in Tanzania, making it the most linguistically diverse country in East Africa; the country does not have a de jure official language.
Swahili is used in parliamentary debate, in the lower courts, as a medium of instruction in primary school. English is used in foreign trade, in diplomacy, in higher courts, as a medium of instruction in secondary and higher education, although the Tanzanian government is planning to discontinue English as a language of instruction altogether. 10 percent of Tanzanians speak Swahili as a first language, up to 90 percent speak it as a second language. The name "Tanzania" was created as a clipped compound of the names of the two states that unified to create the country: Tanganyika and Zanzibar, it comprises the first three letters of the two states, "Tan" and "Zan" as well as the only two vowels in the names of two states, "I" and "a" to form Tanzania. The name "Tanganyika" is derived from the Swahili words tanga and nyika, creating the phrase "sail in the wilderness", it is sometimes understood as a reference to Lake Tanganyika. The name of Zanzibar comes from "zenji", the name for a local people, the Arabic word "barr", which means coast or shore.
The indigenous populations of eastern Africa are thought to be the linguistically isolated Hadza and Sandawe hunter-gatherers of Tanzania. The first wave of migration was by Southern Cushitic speakers who moved south from Ethiopia and Somalia into Tanzania, they are ancestral to the Iraqw and Burunge. Based on linguistic evidence, there may have been two movements into Tanzania of Eastern Cushitic people at about 4,000 and 2,000 years ago, originating from north of Lake Turkana. Archaeological evidence supports the conclusion that Southern Nilotes, including the Datoog, moved south from the present-day South Sudan / Ethiopia border region into central northern Tanzania between 2,900 and 2,400 years ago; these movements took place at the same time as the settlement of the iron-making Mashariki Bantu from West Africa in the Lake Victoria and Lake Tanganyika areas. They brought with them the west African planting tradition and the p
Deciduous
In the fields of horticulture and botany, the term deciduous means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves in the autumn. The term deciduous means "the dropping of a part, no longer needed" and the "falling away after its purpose is finished". In plants, it is the result of natural processes. "Deciduous" has a similar meaning when referring to animal parts, such as deciduous antlers in deer, deciduous teeth in some mammals. Wood from deciduous trees is used in a variety of ways in several industries including lumber for furniture and flooring, bowling pins and baseball bats and furniture, cabinets and paneling. In botany and horticulture, deciduous plants, including trees and herbaceous perennials, are those that lose all of their leaves for part of the year; this process is called abscission. In some cases leaf loss coincides with winter -- namely in polar climates. In other parts of the world, including tropical and arid regions, plants lose their leaves during the dry season or other seasons, depending on variations in rainfall.
The converse of deciduous is evergreen, where foliage is shed on a different schedule from deciduous trees, therefore appearing to remain green year round. Plants that are intermediate may be called semi-deciduous. Other plants are semi-evergreen and lose their leaves before the next growing season, retaining some during winter or dry periods; some trees, including a few species of oak, have desiccated leaves that remain on the tree through winter. Many deciduous plants flower during the period when they are leafless, as this increases the effectiveness of pollination; the absence of leaves improves wind transmission of pollen for wind-pollinated plants and increases the visibility of the flowers to insects in insect-pollinated plants. This strategy is not without risks, as the flowers can be damaged by frost or, in dry season regions, result in water stress on the plant. There is much less branch and trunk breakage from glaze ice storms when leafless, plants can reduce water loss due to the reduction in availability of liquid water during cold winter days.
Leaf drop or abscission involves complex physiological changes within plants. The process of photosynthesis degrades the supply of chlorophylls in foliage; when autumn arrives and the days are shorter or when plants are drought-stressed, deciduous trees decrease chlorophyll pigment production, allowing other pigments present in the leaf to become apparent, resulting in non-green colored foliage. The brightest leaf colors are produced when days grow short and nights are cool, but remain above freezing; these other pigments include carotenoids that are yellow and orange. Anthocyanin pigments produce red and purple colors, though they are not always present in the leaves. Rather, they are produced in the foliage in late summer, when sugars are trapped in the leaves after the process of abscission begins. Parts of the world that have showy displays of bright autumn colors are limited to locations where days become short and nights are cool. In other parts of the world, the leaves of deciduous trees fall off without turning the bright colors produced from the accumulation of anthocyanin pigments.
The beginnings of leaf drop starts when an abscission layer is formed between the leaf petiole and the stem. This layer is formed in the spring during active new growth of the leaf; the cells are sensitive to a plant hormone called auxin, produced by the leaf and other parts of the plant. When auxin coming from the leaf is produced at a rate consistent with that from the body of the plant, the cells of the abscission layer remain connected; the elongation of these cells break the connection between the different cell layers, allowing the leaf to break away from the plant. It forms a layer that seals the break, so the plant does not lose sap. A number of deciduous plants remove nitrogen and carbon from the foliage before they are shed and store them in the form of proteins in the vacuoles of parenchyma cells in the roots and the inner bark. In the spring, these proteins are used as a nitrogen source during the growth of new leaves or flowers. Plants with deciduous foliage have advantages and disadvantages compared to plants with evergreen foliage.
Since deciduous plants lose their leaves to conserve water or to better survive winter weather conditions, they must regrow new foliage during the next suitable growing season. Evergreens suffer greater water loss during the winter and they can experience greater predation pressure when small. Losing leaves in winter may reduce damage from insects. Removing leaves reduces cavitation which can damage xylem vessels in plants; this allows deciduous plants to have xylem vessels with larger diameters and therefore a greater rate of transpiration during the summer growth period
Australia
Australia the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania and numerous smaller islands. It is the world's sixth-largest country by total area; the neighbouring countries are Papua New Guinea and East Timor to the north. The population of 25 million is urbanised and concentrated on the eastern seaboard. Australia's capital is Canberra, its largest city is Sydney; the country's other major metropolitan areas are Melbourne, Brisbane and Adelaide. Australia was inhabited by indigenous Australians for about 60,000 years before the first British settlement in the late 18th century, it is documented. After the European exploration of the continent by Dutch explorers in 1606, who named it New Holland, Australia's eastern half was claimed by Great Britain in 1770 and settled through penal transportation to the colony of New South Wales from 26 January 1788, a date which became Australia's national day; the population grew in subsequent decades, by the 1850s most of the continent had been explored and an additional five self-governing crown colonies established.
On 1 January 1901, the six colonies federated. Australia has since maintained a stable liberal democratic political system that functions as a federal parliamentary constitutional monarchy, comprising six states and ten territories. Being the oldest and driest inhabited continent, with the least fertile soils, Australia has a landmass of 7,617,930 square kilometres. A megadiverse country, its size gives it a wide variety of landscapes, with deserts in the centre, tropical rainforests in the north-east and mountain ranges in the south-east. A gold rush began in Australia in the early 1850s, its population density, 2.8 inhabitants per square kilometre, remains among the lowest in the world. Australia generates its income from various sources including mining-related exports, telecommunications and manufacturing. Indigenous Australian rock art is the oldest and richest in the world, dating as far back as 60,000 years and spread across hundreds of thousands of sites. Australia is a developed country, with the world's 14th-largest economy.
It has a high-income economy, with the world's tenth-highest per capita income. It is a regional power, has the world's 13th-highest military expenditure. Australia has the world's ninth-largest immigrant population, with immigrants accounting for 26% of the population. Having the third-highest human development index and the eighth-highest ranked democracy globally, the country ranks in quality of life, education, economic freedom, civil liberties and political rights, with all its major cities faring well in global comparative livability surveys. Australia is a member of the United Nations, G20, Commonwealth of Nations, ANZUS, Organisation for Economic Co-operation and Development, World Trade Organization, Asia-Pacific Economic Cooperation, Pacific Islands Forum and the ASEAN Plus Six mechanism; the name Australia is derived from the Latin Terra Australis, a name used for a hypothetical continent in the Southern Hemisphere since ancient times. When Europeans first began visiting and mapping Australia in the 17th century, the name Terra Australis was applied to the new territories.
Until the early 19th century, Australia was best known as "New Holland", a name first applied by the Dutch explorer Abel Tasman in 1644 and subsequently anglicised. Terra Australis still saw occasional usage, such as in scientific texts; the name Australia was popularised by the explorer Matthew Flinders, who said it was "more agreeable to the ear, an assimilation to the names of the other great portions of the earth". The first time that Australia appears to have been used was in April 1817, when Governor Lachlan Macquarie acknowledged the receipt of Flinders' charts of Australia from Lord Bathurst. In December 1817, Macquarie recommended to the Colonial Office. In 1824, the Admiralty agreed that the continent should be known by that name; the first official published use of the new name came with the publication in 1830 of The Australia Directory by the Hydrographic Office. Colloquial names for Australia include "Oz" and "the Land Down Under". Other epithets include "the Great Southern Land", "the Lucky Country", "the Sunburnt Country", "the Wide Brown Land".
The latter two both derive from Dorothea Mackellar's 1908 poem "My Country". Human habitation of the Australian continent is estimated to have begun around 65,000 to 70,000 years ago, with the migration of people by land bridges and short sea-crossings from what is now Southeast Asia; these first inhabitants were the ancestors of modern Indigenous Australians. Aboriginal Australian culture is one of the oldest continual civilisations on earth. At the time of first European contact, most Indigenous Australians were hunter-gatherers with complex economies and societies. Recent archaeological finds suggest. Indigenous Australians have an oral culture with spiritual values based on reverence for the land and a belief in the Dreamtime; the Torres Strait Islanders, ethnically Melanesian, obtained their livelihood from seasonal horticulture and the resources of their reefs and seas. The northern coasts and waters of Australia were visited s
Madagascar
Madagascar the Republic of Madagascar, known as the Malagasy Republic, is an island country in the Indian Ocean 400 kilometres off the coast of East Africa. The nation comprises the island of Madagascar and numerous smaller peripheral islands. Following the prehistoric breakup of the supercontinent Gondwana, Madagascar split from the Indian subcontinent around 88 million years ago, allowing native plants and animals to evolve in relative isolation. Madagascar is a biodiversity hotspot; the island's diverse ecosystems and unique wildlife are threatened by the encroachment of the growing human population and other environmental threats. The first archaeological evidence for human foraging on Madagascar may have occurred as much as 10,000 years ago. Human settlement of Madagascar occurred between 350 BC and 550 AD by Austronesian peoples, arriving on outrigger canoes from Borneo; these were joined around the 9th century AD by Bantu migrants crossing the Mozambique Channel from East Africa. Other groups continued to settle on Madagascar over time, each one making lasting contributions to Malagasy cultural life.
The Malagasy ethnic group is divided into 18 or more subgroups, of which the largest are the Merina of the central highlands. Until the late 18th century, the island of Madagascar was ruled by a fragmented assortment of shifting sociopolitical alliances. Beginning in the early 19th century, most of the island was united and ruled as the Kingdom of Madagascar by a series of Merina nobles; the monarchy ended in 1897 when the island was absorbed into the French colonial empire, from which the island gained independence in 1960. The autonomous state of Madagascar has since undergone four major constitutional periods, termed republics. Since 1992, the nation has been governed as a constitutional democracy from its capital at Antananarivo. However, in a popular uprising in 2009, president Marc Ravalomanana was made to resign and presidential power was transferred in March 2009 to Andry Rajoelina. Constitutional governance was restored in January 2014, when Hery Rajaonarimampianina was named president following a 2013 election deemed fair and transparent by the international community.
Madagascar is a member of the United Nations, the African Union, the Southern African Development Community, the Organisation Internationale de la Francophonie. Madagascar belongs according to the United Nations. Malagasy and French are both official languages of the state; the majority of the population adheres to traditional beliefs, Christianity, or an amalgamation of both. Ecotourism and agriculture, paired with greater investments in education and private enterprise, are key elements of Madagascar's development strategy. Under Ravalomanana, these investments produced substantial economic growth, but the benefits were not evenly spread throughout the population, producing tensions over the increasing cost of living and declining living standards among the poor and some segments of the middle class; as of 2017, the economy has been weakened by the 2009–2013 political crisis, quality of life remains low for the majority of the Malagasy population. In the Malagasy language, the island of Madagascar is called Madagasikara and its people are referred to as Malagasy.
The island's appellation "Madagascar" is not of local origin but rather was popularized in the Middle Ages by Europeans. The name Madageiscar was first recorded in the memoirs of 13th-century Venetian explorer Marco Polo as a corrupted transliteration of the name Mogadishu, the Somali port with which Polo had confused the island. On St. Laurence's Day in 1500, Portuguese explorer Diogo Dias landed on the island and named it São Lourenço. Polo's name popularized on Renaissance maps. No single Malagasy-language name predating Madagasikara appears to have been used by the local population to refer to the island, although some communities had their own name for part or all of the land they inhabited. At 592,800 square kilometres, Madagascar is the world's 47th largest country and the fourth-largest island; the country lies between latitudes 12°S and 26°S, longitudes 43°E and 51°E. Neighboring islands include the French territory of Réunion and the country of Mauritius to the east, as well as the state of Comoros and the French territory of Mayotte to the north west.
The nearest mainland state is Mozambique, located to the west. The prehistoric breakup of the supercontinent Gondwana separated the Madagascar–Antarctica–India landmass from the Africa–South America landmass around 135 million years ago. Madagascar split from India about 88 million years ago during the late Cretaceous period allowing plants and animals on the island to evolve in relative isolation. Along the length of the eastern coast runs a narrow and steep escarpment containing much of the island's remaining tropical lowland forest. To the west of this ridge lies a plateau in the center of the island ranging in altitude from 750 to 1,500 m above sea level; these central highlands, traditionally the homeland of the Merina people and the location of their historic capital at Antananarivo, are the most densely populated part of the island and are characterized by terraced, rice-growing valleys lying between grassy hills and patches of the subhumid forests that covered the highland region. To the west of the highlands, the arid terrain slope
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