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48-794: The Precambrian to Cenozoic Aïr Mountains consist of peralkaline granite intrusions which appear dark in colour (unusual since most granitic masses are light-toned in the field). In the Sahara Desert such mountains often stand out in stark relief as topographic heights amidst lowlands covered by sand. The terrain consists of high plateau, mountain ranges, and broad, sandy valleys and seasonal wadis which once contained rivers. Areas of these deep, often intersecting, valleys also contain waterborne clay and silt deposits. Underground watercourses in some of these valleys continue to provide year-round oasis and seasonal vegetation. The Aïr mountains themselves consist of nine almost circular massifs rising from

96-708: A supereon , but this is also an informal term, not defined by the ICS in its chronostratigraphic guide. Eozoic (from eo- "earliest") was a synonym for pre-Cambrian , or more specifically Archean . A specific date for the origin of life has not been determined. Carbon found in 3.8 billion-year-old rocks (Archean Eon) from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have been found in Western Australia . Probable fossils 100 million years older have been found in

144-541: A Saharan matrix, these species have a high conservation value. The town of Agadez in the heart of the Tuareg country is the capital of Aïr. Much of the Tuareg population of Aïr until recently led a nomadic life, relying essentially on camel and goats from which they take milk, meat and skins used in the production of local handicrafts. Most sedentary populations were either dependents of higher caste Tuareg pastoralists or

192-525: A Saharan-Mediterranean distribution. Three ferns were found for the first time in the Aïr recently, Cheilanthes coriacea , Actiniopteris radiata , and Ophioglossum polyphyllum , suggesting that ferns may be more prone to develop in arid environments than commonly proposed. All these data evidence a marked mountain climatic specificity in the Aïr, with a positive impact on species richness and species diversity. Because of their strong geographic isolation within

240-402: A gland at the bottom of the last pair of pinnulae. Flowers in globulous heads 1.2–1.5 cm in diameter of a bright golden-yellow color, set up either axillary or whorly on peduncles 2–3 cm long located at the end of the branches. Pods are strongly constricted, hairy, white-grey, thick and softly tomentose. Its seeds number approximately 8000/kg. Acacia nilotica or Vachellia nilotica

288-735: A possible 2450 Ma red alga from the Kola Peninsula , 1650 Ma carbonaceous biosignatures in north China, the 1600 Ma Rafatazmia , and a possible 1047 Ma Bangiomorpha red alga from the Canadian Arctic. The earliest fossils widely accepted as complex multicellular organisms date from the Ediacaran Period. A very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as Ediacaran or Vendian biota . Hard-shelled creatures appeared toward

336-573: A promising restoration tool to be used by local inhabitants. In comparison, mountainous areas are even less documented. Tropical tree species less resistant to drought have been described in the highlands, among which the Fabaceae Senegalia laeta and Vachellia seyal . Quezel has observed the remnant presence of a rare endemic taxon related to the olive in the northern sector of the Aïr range. Recently, this taxon, Olea europaea subsp. laperrinei , has been found in other mountains of

384-515: A reddish-tinge. The tender twig of this plant is used as a toothbrush in south-east Africa and the Indian subcontinent.   The exudate gum of this tree is known as gum arabic and has been collected from the pharaonic times for the manufacture of medicines, dyes and paints. In the present commercial market, gum arabic is defined as the dried exudate from the trunks and branches of Senegalia (Acacia) senegal or Vachellia (Acacia) seyal in

432-612: A rocky plateau, bordered by the sand dunes and plain of the Ténéré Desert to the east. The massif is a plateau consisting of a sub- Cambrian age erosion surface on Precambrian metamorphic rocks , punctuated by a series of flat-topped, granite intrusion peaks, which include Mont Idoukal-n-Taghès (Niger's highest point at 2022 m), Mont Tamgak (1988 m), Mont Greboun (1944 m), Adrar Bous , Fadei , Chirriet , Taghmert , Agueraguer , Takaloukouzet , and Goundai . The massif contains volcanic features including

480-468: Is a tree 5–20 m high with a dense spheric crown , stems and branches usually dark to black coloured, fissured bark, grey-pinkish slash, exuding a reddish low quality gum. The tree has thin, straight, light, grey spines in axillary pairs, usually in 3 to 12 pairs, 5 to 7.5 cm (3 in) long in young trees, mature trees commonly without thorns. The leaves are bipinnate, with 3–6 pairs of pinnulae and 10–30 pairs of leaflets each, tomentose, rachis with

528-515: Is also very popular with cattle. Pods are used as a supplement to poultry rations in India. Dried pods are particularly sought out by animals on rangelands. In India branches are commonly lopped for fodder . In West Africa, the pods and leaves are considered to have anthelminthic properties on small ruminants and this has been confirmed by in vitro experiments on nematodes . In Kano of Nigeria , acacia pods have traditionally been used to dye leather

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576-664: Is known to occur during the RNA replication of extant coronaviruses . Evidence of the details of plate motions and other tectonic activity in the Precambrian is difficult to interpret. It is generally believed that small proto-continents existed before 4280 Ma, and that most of the Earth's landmasses collected into a single supercontinent around 1130 Ma. The supercontinent, known as Rodinia , broke up around 750 Ma. A number of glacial periods have been identified going as far back as

624-576: Is native from Egypt , across the Maghreb and Sahel , south to Mozambique and KwaZulu-Natal , South Africa, and east through the Arabian Peninsula to the Indian subcontinent and Burma . It has become widely naturalised outside its native range including Zanzibar and Australia. It is spread by livestock. In part of its range smallstock consume the pods and leaves, but elsewhere it

672-668: Is the earliest part of Earth's history , set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian , the first period of the Phanerozoic Eon , which is named after Cambria , the Latinized name for Wales , where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time. The Precambrian is an informal unit of geologic time, subdivided into three eons ( Hadean , Archean , Proterozoic ) of

720-521: Is thought that the Earth coalesced from material in orbit around the Sun at roughly 4,543 Ma, and may have been struck by another planet called Theia shortly after it formed, splitting off material that formed the Moon (see Giant-impact hypothesis ). A stable crust was apparently in place by 4,433 Ma, since zircon crystals from Western Australia have been dated at 4,404 ± 8 Ma. The term "Precambrian"

768-418: Is thought to have formed about 1300-900 Ma, to have included most or all of Earth's continents and to have broken up into eight continents around 750–600 million years ago. Vachellia nilotica Vachellia nilotica , more commonly known as Acacia nilotica , and by the vernacular names of gum arabic tree , babul , thorn mimosa , Egyptian acacia or thorny acacia , is a flowering tree in

816-731: Is used by geologists and paleontologists for general discussions not requiring a more specific eon name. However, both the United States Geological Survey and the International Commission on Stratigraphy regard the term as informal. Because the span of time falling under the Precambrian consists of three eons (the Hadean , the Archean , and the Proterozoic ), it is sometimes described as

864-534: The Huronian epoch, roughly 2400–2100 Ma. One of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a " Snowball Earth ". The atmosphere of the early Earth is not well understood. Most geologists believe it was composed primarily of nitrogen, carbon dioxide, and other relatively inert gases, and

912-558: The Ikelan ( Bouzou in Hausa / Bella in Songhai ), Tuareg slaves. These peoples were settled in northern oases, to tend the date palm plantations held by the noble clans. Agriculture products from oases such as Timia , Aouderas and Tabelot are traditionally exchanged against clothes, or salt, brought by camel caravans ( Azalai ) from the remote Tenere oases of Bilma and Fachi to

960-522: The geologic time scale . It spans from the formation of Earth about 4.6 billion years ago ( Ga ) to the beginning of the Cambrian Period, about 538.8 million years ago ( Ma ), when hard-shelled creatures first appeared in abundance. Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history , and what is known has largely been discovered from

1008-482: The oxygen catastrophe . At first, oxygen would have quickly combined with other elements in Earth's crust, primarily iron, removing it from the atmosphere. After the supply of oxidizable surfaces ran out, oxygen would have begun to accumulate in the atmosphere, and the modern high-oxygen atmosphere would have developed. Evidence for this lies in older rocks that contain massive banded iron formations that were laid down as iron oxides. A terminology has evolved covering

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1056-682: The principle of priority , which would normally prevent such a taxonomic change, was waived with a majority vote by the International Botanical Congress in 2005. The renaming of the traditional Acacia to Vachellia remains controversial, especially in Africa, where V. nilotica is an iconic species and is widely referred to as "the acacia". For the new classification of this and other species historically classified under genus Acacia , see Acacia . The genus name Acacia derives from ἀκακία , which may come from

1104-645: The 1880s, Toubu raids increased, and when the Tuareg Ag Mohammed Wau Teguidda Kaocen rose against the French in 1917, many towns were destroyed on his way to the siege of Agadez. When the French retook Agadez, a brutal punitive expedition through the Aïr left many formerly populous places abandoned, razed by Kaosen and the French successively. While the Kel Owey continued to dominate the settled oasis towns and pastoral herding,

1152-401: The 1960s onwards. The Precambrian fossil record is poorer than that of the succeeding Phanerozoic , and fossils from the Precambrian (e.g. stromatolites ) are of limited biostratigraphic use. This is because many Precambrian rocks have been heavily metamorphosed , obscuring their origins, while others have been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata. It

1200-725: The Aïr mountains. The location of the Aïr as a southern extension of the Hoggar mountain range makes it a connection between the Saharan Flora and the Sahelian Flora. However, the presence of mountains up to 2000 m a.s.l. generates locally favourable conditions for several species of the Sudanian zone and the Mediterranean zone. During the 20th century a series of scientific missions in the Aïr has permitted to identify

1248-656: The Aïr: these very isolated, small populations represent the southern limit of the species distribution. A study led on the slopes of the highest summit in the Aïr, Mont Idoukal-n-Taghès (2022 m a.s.l.), identified plant species that had never been inventoried in Niger before. Among them, Pachycymbium decaisneanum , Cleome aculeata , Echinops mildbraedii and Indigofera nummularia are tropical species with relatively low resistance to water stress, whereas Silene lynesii , Tephrosia elegans , and Echinops mildbraedii have

1296-673: The ancient Greek word ἄκις , ákis , "thorn", for its characteristic thorns, or may have been borrowed from a pre-Greek language. The specific epithet nilotica was probably given by Linnaeus from the tree's originally known range along the Nile river. In Australia the tree is known as a prickly acacia , despite usurping Dioscorides' two millennia-old etymology, the Australian species classified as Acacia in Australia do not have thorns. Acacia nilotica or Vachellia nilotica

1344-629: The area since at least the twelfth century. Agadez, as well as In-Gall to the east, were the farthest outposts of the Songhai Empire in the early 15th century. In the sixteenth century, the area fell under the newly created Tuareg Sultanate of Agadez , and remained so until the arrival of the French at the end of the 19th. The emergence of the French weakened the Tuareg Kels and provoked both infighting and resistance to colonialism. From

1392-401: The current scheme based upon numerical ages. Such a system could rely on events in the stratigraphic record and be demarcated by GSSPs . The Precambrian could be divided into five "natural" eons, characterized as follows: The movement of Earth's plates has caused the formation and break-up of continents over time, including occasional formation of a supercontinent containing most or all of

1440-621: The dry wadi river valleys (known by the Hausa term " Kori ") channel and hold rainwater in gueltas (stone pools, such as that near the town of Timia ), creating oases which provide forage for animals, and in some areas, farming. The high Bagzane plateau of the central Aïr in particular provides adequate rainfall for intensive agriculture. Other, vast, areas of the region are entirely devoid of plant life and with their volcanic protrusions and rock fields present an otherworldly appearance. More than 430 vascular species have been recorded so far in

1488-453: The early years of the Earth's existence, as radiometric dating has allowed absolute dates to be assigned to specific formations and features. The Precambrian is divided into three eons: the Hadean (4567.3–4031 Ma), Archean (4031-2500 Ma) and Proterozoic (2500-538.8 Ma). See Timetable of the Precambrian . It has been proposed that the Precambrian should be divided into eons and eras that reflect stages of planetary evolution, rather than

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1536-482: The east. The Aïr is known for its rock art , dating from 6000 BCE to around 1000CE. During the African humid period , the region was a pastoral area, as is illustrated by images of cattle and large mammals. During the 3rd millennium BC, however, a process of desertification began and the Tuareg from further north migrated into the region. Later art indicated war, depicting horses and chariots . In particular,

1584-705: The end of that time span, marking the beginning of the Phanerozoic Eon. By the middle of the following Cambrian Period, a very diverse fauna is recorded in the Burgess Shale , including some which may represent stem groups of modern taxa. The increase in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life. While land seems to have been devoid of plants and animals, cyanobacteria and other microbes formed prokaryotic mats that covered terrestrial areas. Tracks from an animal with leg-like appendages have been found in what

1632-518: The extinct caldera of Arakao, Cenozoic lava flows of hawaiite to trachyte composition, volcanic cones , tuff rings and one of the largest ring dike systems in the world. At Izouzaoenehe, lie the marble Blue Mountains , and the lower Zagado valley is surrounded by white marble hills. Carboniferous sandstone and coal units in the Iullemmeden Basin just to the west of the massif contain uranium mineralisation sourced from

1680-601: The family Fabaceae . It is native to Africa, the Middle East and the Indian subcontinent . It is also considered a ' weed of national significance ' and an invasive species of concern in Australia, as well as a noxious weed by the federal government of the United States. This species of tree is the type species of the Linnaean genus Acacia , which derives its name from Greek ἀκακία , akakía ,

1728-458: The family Leguminosae (Fabaceae). The gum of A. nilotica is also referred to in India as Amaravati gum . The tree's wood is "very durable if water-seasoned " and its uses include tool handles and lumber for boats. The wood has a density of about 833 kg/m . In India it's used as an ingredient in various dishes. The Maasai people eat both the inner bark ( phloem ) and the fruit pulp boiled in water. The East african tribes living on

1776-416: The five-meter-high carvings of the " Dabous Giraffes " discovered in 1999 is internationally famous. Cave art in the region is predominantly stone carving , initially with sharp rock, and from around 1200 BC perhaps with metal. When the Tuareg tribes were pushed south by Arab invaders in the eighth and ninth centuries, there were Gobirwa Hausa in the southern Aïr. Successive Tuareg Kel s have controlled

1824-490: The granites of the massif. Because of its altitude (on average between 500 and 900 m) and despite its low rainfall (50 to 160 mm/year on the lower plateau), the Aïr forms a green region in comparison with the surrounding deserts, especially after the August–September seasonal rains. The climate is classified as Sahel , like that of the regions well to its south. While the mountains are largely bare of vegetation,

1872-431: The intermountain zone of the Aïr a particularly harsh place for plants to develop. The additional presence of domestic herbivores has led to a severe deficit in tree regeneration, which has been cited as a major ecological concern. Tree regeneration has been observed enhanced as soon as tree seedlings are protected by large tussocks of the frequent grass Panicum turgidum . This positive interaction between plants represents

1920-541: The landmass. The earliest known supercontinent was Vaalbara . It formed from proto-continents and was a supercontinent 3.636 billion years ago. Vaalbara broke up c. 2.845–2.803 Ga ago. The supercontinent Kenorland was formed c. 2.72 Ga ago and then broke sometime after 2.45–2.1 Ga into the proto-continent cratons called Laurentia , Baltica , Yilgarn craton and Kalahari . The supercontinent Columbia , or Nuna, formed 2.1–1.8 billion years ago and broke up about 1.3–1.2 billion years ago. The supercontinent Rodinia

1968-461: The majority of plant species developing in the Aïr. Vachellia tortilis , subsp. raddiana ( afagag ) and Balanites aegyptiaca ( aborak ) are among the most frequent tree species in the intermountain zone. In the vicinity of temporary rivers named koris , species like Vachellia nilotica , Faidherbia albida and the palm Hyphaene thebaica coexist with date palm cultivars ( Phoenix dactylifera ). Severe droughts and high aridity have made

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2016-421: The name given by early Greek botanist-physician Pedanius Dioscorides ( c.  40–90 CE) to this tree as a medicinal, in his book Materia Medica . The genus Acacia was long known not to be taxonomically monophyletic, and despite being the type species of that genus, A. nilotica has since been moved to the genus Vachellia , with the genus name Acacia being reserved for Australian species;

2064-526: The same area. However, there is evidence that life could have evolved over 4.280 billion years ago. There is a fairly solid record of bacterial life throughout the remainder (Proterozoic Eon) of the Precambrian. Complex multicellular organisms may have appeared as early as 2100 Ma. However, the interpretation of ancient fossils is problematic, and "... some definitions of multicellularity encompass everything from simple bacterial colonies to badgers." Other possible early complex multicellular organisms include

2112-403: The savanna use this plant medicinally to treat sore throat, cough, chest pains etc. In Northern Nigeria it is called bagaruwa in Hausa . Medicinal uses include soaking the tender bark in water to be taken against dysentery and pile. The fruits are ground together with the seeds and taken with honey as treatment against stomach ulcers. Two new antiprotozoal diterpenes have been isolated from

2160-421: The sedentary farmers (Tuareg, Hausa, or Songhai) expanded farming and sedentary livestock cultivation in the mid-20th century. The famines of the 1970s and 1980s brought an end to this expansion, and as Agadez and Arlit grew, the towns of the Aïr have shrunk. The first Tuareg rebellion of 1990-95 saw brutal government reprisals which depopulated many villages in the Aïr. Peace from the mid-1990s, as well as

2208-631: The uranium mines of Arlit brought unprecedented growth to the region, with many small towns gaining valuable tourism revenue. In 2004, a locust invasion ravaged many gardens, bringing scarcity and contributing to the Second Tuareg Rebellion of 2007–2009. Unrest continues in the region, effectively ending the nascent tourist industry. Precambrian The Precambrian ( / p r i ˈ k æ m b r i . ə n , - ˈ k eɪ m -/ pree- KAM -bree-ən, -⁠KAYM- ; or Pre-Cambrian , sometimes abbreviated pC , or Cryptozoic )

2256-482: Was lacking in free oxygen . There is, however, evidence that an oxygen-rich atmosphere existed since the early Archean. At present, it is still believed that molecular oxygen was not a significant fraction of Earth's atmosphere until after photosynthetic life forms evolved and began to produce it in large quantities as a byproduct of their metabolism . This radical shift from a chemically inert to an oxidizing atmosphere caused an ecological crisis , sometimes called

2304-852: Was mud 551 million years ago. The RNA world hypothesis asserts that RNA evolved before coded proteins and DNA genomes. During the Hadean Eon (4,567–4,031 Ma) abundant geothermal microenvironments were present that may have had the potential to support the synthesis and replication of RNA and thus possibly the evolution of a primitive life form. It was shown that porous rock systems comprising heated air-water interfaces could allow ribozyme - catalyzed RNA replication of sense and antisense strands that could be followed by strand-dissociation, thus enabling combined synthesis, release and folding of active ribozymes. This primitive RNA replicative system also may have been able to undergo template strand switching during replication ( genetic recombination ) as

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