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Desert Varnish
Desert varnish or rock varnish is an orange-yellow to black coating found on exposed rock surfaces in arid environments. Desert varnish is approximately one micrometer thick and exhibits nanometer-scale layering. Rock rust and desert patina are other terms which are also used for the condition, but less often. Formation Desert varnish forms only on physically stable rock surfaces that are no longer subject to frequent precipitation, fracturing or wind abrasion. The varnish is primarily composed of particles of clay along with oxides of iron and manganese. There is also a host of trace elements and almost always some organic matter. The color of the varnish varies from shades of brown to black. It has been suggested that desert varnish should be investigated as a potential candidate for a "shadow biosphere". However, a 2008 microscopy study posited that desert varnish has already been reproduced with chemistry not involving life in the lab, and that the main component is actuall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Desert Varnish
Desert varnish or rock varnish is an orange-yellow to black coating found on exposed rock surfaces in arid environments. Desert varnish is approximately one micrometer thick and exhibits nanometer-scale layering. Rock rust and desert patina are other terms which are also used for the condition, but less often. Formation Desert varnish forms only on physically stable rock surfaces that are no longer subject to frequent precipitation, fracturing or wind abrasion. The varnish is primarily composed of particles of clay along with oxides of iron and manganese. There is also a host of trace elements and almost always some organic matter. The color of the varnish varies from shades of brown to black. It has been suggested that desert varnish should be investigated as a potential candidate for a "shadow biosphere". However, a 2008 microscopy study posited that desert varnish has already been reproduced with chemistry not involving life in the lab, and that the main component is actuall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microbe
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in older texts. The informal synonym ''microbe'' () comes from μικρός, mikrós, "small" and βίος, bíos, "life". is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from sixth century BC India. The scientific study of microorganisms began with their observation under the microscope in the 1670s by Anton van Leeuwenhoek. In the 1850s, Louis Pasteur found that microorganisms caused food spoilage, debunking the theory of spontaneous generation. In the 1880s, Robert Koch discovered that microorganisms caused the diseases tuberculosis, cholera, diphtheria, and anthrax. Because ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wadi Saham
Wadi Saham is a seasonal watercourse in the Hajar Mountains of Fujairah, in the United Arab Emirates. It is notable for its petroglyphs, including a single rock bearing 26 petroglyphs across four faces. Petroglyphs and other finds The Wadi Saham is located to the West of Fujairah City and consists mainly of a rocky wadi floor with scree and mountain walls. The largest petroglyph assemblage in the wadi is focused on a single rock, to the side of the road, with a large number of horse riders depicted, as well as geometric shapes such as the letter I and cruciform images. The petroglyphs have to a large extent been preserved by a natural bacterial deposit, known as desert varnish. Similar petroglyphs have also been found in the nearby sites of Wadi Hayl, ''Hassat Al Risoom'' (literally 'Rock with Drawings') close to the village of Roweida, and Wadi Al Shanah. They have been dated to between 1300 and 300 BCE. Some dates for the petroglyphs have been advanced as early as the Bronze Age ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Iron Age In The United Arab Emirates
The territory currently known as the United Arab Emirates was home to three distinct Iron Age periods. Iron Age I spanned 1,200–1,000 BCE, Iron Age II from 1,000–600 BCE, and Iron Age III from 600–300 BCE. This period of human development in the region was followed by the Mleiha or Late Pre-Islamic era, from 300 BCE onwards through to the Islamic era which commenced with the culmination of the 7th century Ridda Wars. To some degree the term 'Iron Age' is misapplied, as little evidence exists for any indigenous iron-work outside the finds at Muweilah, themselves thought to be imports, and even the extensive evidence of smelting throughout the Iron Age found at Saruq Al Hadid is dominated by copper and tin production. Finds from the important site of Tell Abraq have been crucial in the division of the three Iron Age periods in the UAE. P. Hellyer, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite.Blatt, Harvey and Robert J. Tracy (1996) ''Petrology: Igneous, Sedimentary and Metamorphic'', 2nd ed., Freeman, pp. 281–292 Shale is characterized by its tendency to split into thin layers ( laminae) less than one centimeter in thickness. This property is called '' fissility''. Shale is the most common sedimentary rock. The term ''shale'' is sometimes applied more broadly, as essentially a synonym for mudrock, rather than in the more narrow sense of clay-rich fissile mudrock. Texture Shale typically exhibits varying degrees of fissility. Because of the parallel orientation of clay mineral flakes in shale, it breaks into thin layers, often splintery and usually parallel to the otherwise indistinguishable bedding ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metamorphic Rock
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causing profound physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith may be an igneous, sedimentary, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by their protolith, their chemical and mineral makeup, and their texture. They may be formed simply by being deeply buried beneath the Earth's surface, where they are subject to high temperatures and the great pressure of the rock layers above. They can also form from tectonic processes such as continental collisions, which cause horizontal pressure, friction, and dis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quartzite
Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of hematite. Other colors, such as yellow, green, blue and orange, are due to other minerals. The term ''quartzite'' is also sometimes used for very hard but unmetamorphosed sandstones that are composed of quartz grains thoroughly cemented with additional quartz. Such sedimentary rock has come to be described as orthoquartzite to distinguish it from metamorphic quartzite, which is sometimes called metaquartzite to emphasize its metamorphic origins. Quartzite is very resistant to chemical weathering and often forms ridges and resistant hilltops. The nearly pure silica co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro. The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System. For example, the bulk of the plains of Venus, which cover ~80% of the surface, are basaltic; the lunar maria are plains of flood-basaltic lava flows; and basalt is a common rock on the surface of Mars. Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flows that can spread over great areas before cooling and solidifying. Flood basalts are t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life. About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite, a closely related rock, which contains a high percentage of the mineral dolomite, . ''Magnesian limestone'' is an obsolete and poorly-defined term used variously for dolomite, for limes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Petroglyph
A petroglyph is an image created by removing part of a rock surface by incising, picking, carving, or abrading, as a form of rock art. Outside North America, scholars often use terms such as "carving", "engraving", or other descriptions of the technique to refer to such images. Petroglyphs are found worldwide, and are often associated with prehistoric peoples. The word comes from the Greek prefix , from meaning "stone", and meaning "carve", and was originally coined in French as . Another form of petroglyph, normally found in literate cultures, a rock relief or rock-cut relief is a relief sculpture carved on "living rock" such as a cliff, rather than a detached piece of stone. While these relief carvings are a category of rock art, sometimes found in conjunction with rock-cut architecture, they tend to be omitted in most works on rock art, which concentrate on engravings and paintings by prehistoric or nonliterate cultures. Some of these reliefs exploit the rock' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Native Americans In The United States
Native Americans, also known as American Indians, First Americans, Indigenous Americans, and other terms, are the Indigenous peoples of the mainland United States ( Indigenous peoples of Hawaii, Alaska and territories of the United States are generally known by other terms). There are 574 federally recognized tribes living within the US, about half of which are associated with Indian reservations. As defined by the United States Census, "Native Americans" are Indigenous tribes that are originally from the contiguous United States, along with Alaska Natives. Indigenous peoples of the United States who are not listed as American Indian or Alaska Native include Native Hawaiians, Samoan Americans, and the Chamorro people. The US Census groups these peoples as " Native Hawaiian and other Pacific Islanders". European colonization of the Americas, which began in 1492, resulted in a precipitous decline in Native American population because of new diseases, wars, ethni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Valley Of Fire Petroglyphs
A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams over a very long period. Some valleys are formed through erosion by glacial ice. These glaciers may remain present in valleys in high mountains or polar areas. At lower latitudes and altitudes, these glacially formed valleys may have been created or enlarged during ice ages but now are ice-free and occupied by streams or rivers. In desert areas, valleys may be entirely dry or carry a watercourse only rarely. In areas of limestone bedrock, dry valleys may also result from drainage now taking place underground rather than at the surface. Rift valleys arise principally from earth movements, rather than erosion. Many different types of valleys are described by geographers, using terms that may be global in use or else applied only locally. F ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
