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29-582: The Nimba Range is a narrow ridge extending approximately 40 km long, with an orientation of northeast–southwest. It is composed mostly of Precambrian rock, including granite and quartzite which contain deposits of iron ore . Mining of top-quality iron-ore poses the major threat to the unique geomorphology and wildlife. There are about fifty springs, including the origins of the Cavally , Cestos , and Sassandra Rivers . Rainfall varies greatly with elevation and season. About 3,000 mm of rain falls at

58-708: 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

87-735: 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

116-441: Is a part of a distinct freshwater ecoregion with a high portion of endemic aquatic species. The plant communities vary with altitude and cardinal orientation. The Guinean montane forests ecoregion covers the portion of the range above 600 meters elevation. Major plant communities in the ecoregion include montane grasslands and savannas, cloud forests, and lower montane forests. High-altitude grasslands and montane savannas cover

145-644: Is a threatened species found on Mt. Nimba and other peaks in the Guinea Highlands. It is found in high-altitude grassland and in gallery forests during the dry season. Ptychadena submascareniensis is another frog species that has been found only on Mount Nimba and in the Loma Mountains of Sierra Leone . Below the highest peaks, montane grasslands interspersed by gallery forests, between 1,200 and 1,400 meters. Above 900 meters elevation, near-daily mist and clouds support cloud forests , dominated by

174-664: 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

203-668: 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

232-521: 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"

261-432: 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. Ochna 79; see text Ochna is a genus comprising 79 species of evergreen trees , shrubs and shrublets belonging to the flowering plant family Ochnaceae . These species are native to tropical woodlands of Africa , Madagascar ,

290-731: 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

319-534: 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

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348-640: The Mascarenes and Asia .  Species of this genus are usually called ochnas , bird's-eye bushes or Mickey-mouse plants , a name derived from the shape of the drupelet fruit . The name of this genus comes from the Greek word ὄχνη ( ókhnē ), used by Theocritus and meaning "wild pear", as the leaves are similar in appearance. Some species, including Ochna integerrima (yellow Mai flower) and O. serrulata (bird's eye plant), are cultivated as decorative plants . Species of this genus are found in

377-522: 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

406-482: 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

435-401: 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

464-608: The Guinea Plum tree ( Parinari excelsa ), trees of the Myrtle family ( Myrtaceae ), including Syzygium guineense , and species of Ochna and Gaertnera . The moist climate supports many epiphytes , including an endemic orchid , Rhipidoglossum paucifolium . Lower montane forests of Lophira procera , Tarrietia utilis , Mapania spp., Chlorophora regia , Morus mesozygia , and Terminalia ivorensis occur between 600 and 900 meters elevation. Below 600 meters,

493-751: The Nimba Range includes frogs, fish, the Nimba Stream Crab (Liberonautes nimba) , and the endangered Nimba otter shrew (Micropotamogale lamottei) . The African clawless otter (Aonyx capensis) also inhabits the mountain streams. Species richness is high among aquatic invertebrates, including 81 species of dragonflies . The WWF designates the Nimba Range a distinct freshwater ecoregion because of its moderate species richness and high proportion of endemic aquatic species, particularly among fish and amphibians. The Nimba Range's high elevation, its rapids and waterfalls that isolate habitat areas, and

522-703: The colonial government established a Strict Nature Reserve in the Ivory Coast section of the range. It was extended into Guinea the following year. The area remained protected after Guinea and Ivory Coast became independent. UNESCO declared Mount Nimba a biosphere reserve in 1980, and a World Heritage Site shortly thereafter. 7°34′N 8°28′W  /  7.567°N 8.467°W  / 7.567; -8.467 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 )

551-401: 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

580-453: 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

609-705: 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

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638-1079: The highest altitudes, and between 700 and 1,200 mm at the lower elevations. In fact, some parts of the mountain receive less precipitation, due to rain-shadow effect of the high ridge. Most of the rainfall occurs between May and October. The Nimba Range harbours an especially rich flora and fauna, and it is the home of more than 2000 vascular plant species, 317 vertebrate species, 107 of which are mammals , and to more than 2,500 invertebrate species. Notably endemic vertebrates are Nimba viviparous toad , Lamotte's roundleaf bat , Myotis nimbaensis , and Nimba otter shrew . Other rare and endangered animals are West African lion , pygmy hippopotamus , zebra duiker , and western chimpanzee that uses stones as tools. The range has been designated an Important Bird Area (IBA) by BirdLife International because it supports significant populations of many bird species. Terrestrial ecoregions include Western Guinean lowland forest , Guinean montane forest , Guinean forest-savanna mosaic , and West Sudanian savanna . The Nimba Range

667-475: The highest peaks, dominated by the grass Loudetia kagerensis . The grasslands are home to one endemic fern, Asplenium schnellii , and two endemic flowering plants, Osbeckia porteresii and Blaeria nimbana . Shrubs, including Protea occidentalis , inhabit the slopes. The endemic frog species Nimbaphrynoides occidentalis , which inhabits the montane grasslands of the range, is totally viviparous . The Guinea Screeching Frog ( Arthroleptis crusculum )

696-541: 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

725-482: The montane forests transition to the Western Guinean lowland forests ecoregion. The mountain is surrounded by Guinean forest-savanna mosaic, and West Sudanian savanna . Swift-running streams descend steep slopes of the range, and often experience torrential floods during the rainy season. Rheophytes , plants that can live in running water, dominate the aquatic vegetation. The endemic aquatic animals in

754-526: 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

783-411: The stability of the aquatic environment, have promoted speciation . The Guinean Highlands , of which the Nimba Range are part, separate the coastal rivers and streams of Upper Guinea from the upper Niger River basin. The highlands form a barrier to movement of aquatic species between these freshwater regions. The fish fauna of the Nimba Range shares affinities with that of Upper Guinea . In 1943,

812-482: 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

841-852: 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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