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Earth's Mantle
Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of 4.01 × 1024 kg and thus makes up 67% of the mass of Earth. It has a thickness of making up about 84% of Earth's volume. It is predominantly solid but, on geologic time scales, it behaves as a viscous fluid, sometimes described as having the consistency of caramel. Partial melting of the mantle at mid-ocean ridges produces oceanic crust, and partial melting of the mantle at subduction zones produces continental crust. Structure Rheology Earth's mantle is divided into two major rheological layers: the rigid lithosphere comprising the uppermost mantle, and the more ductile asthenosphere, separated by the lithosphere-asthenosphere boundary. Lithosphere underlying ocean crust has a thickness of around 100 km, whereas lithosphere underlying continental crust generally has a thickness of 150–200 km. The lithosphere and overlying crust make up tectonic plates, which mov ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth Poster
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surface is made up of the ocean, dwarfing Earth's polar ice, lakes, and rivers. The remaining 29% of Earth's surface is land, consisting of continents and islands. Earth's surface layer is formed of several slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth's liquid outer core generates the magnetic field that shapes the magnetosphere of the Earth, deflecting destructive solar winds. The atmosphere of the Earth consists mostly of nitrogen and oxygen. Greenhouse gases in the atmosphere like carbon dioxide (CO2) trap a part of the energy from the Sun close to the surface. Water vapor is widely present in the atmosphere and forms clouds that cover most of the planet. More solar energy is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet, dwarf planet, or natural satellite. It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase (solid crust vs. liquid mantle). The crusts of Earth, Mercury, Venus, Mars, Io, the Moon and other planetary bodies formed via igneous processes and were later modified by erosion, impact cratering, volcanism, and sedimentation. Most terrestrial planets have fairly uniform crusts. Earth, however, has two distinct types: continental crust and oceanic crust. These two types have different chemical compositions and physical properties and were formed by different geological processes. Types of crust Planetary geologists divide crust into three categories based on how and when it formed. Primary crust / primordial crust This is a planet's "original" crust. It forms from solidification of a magma ocean. Towa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Large Low-shear-velocity Provinces
Large low-shear-velocity provinces, LLSVPs, also called LLVPs or superplumes, are characteristic structures of parts of the lowermost mantle (the region surrounding the outer core) of Earth. These provinces are characterized by slow shear wave velocities and were discovered by seismic tomography of deep Earth. There are two main provinces: the African LLSVP and the Pacific LLSVP. Both extend laterally for thousands of kilometers and possibly up to vertically from the core–mantle boundary. The Pacific LLSVP is across, and underlies four hotspots that suggest multiple mantle plumes underneath. These zones represent around 8% of the volume of the mantle (6% of Earth). Other names for LLSVPs include " superswells", "thermo-chemical piles", or "hidden reservoirs". Most of these names, however, are more interpretive of their proposed geodynamical or geochemical effects. For example, the name "thermo-chemical pile" interprets LLSVPs as lower-mantle piles of thermally hot and/or chemi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
D Double-prime
D, or d, is the fourth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''dee'' (pronounced ), plural ''dees''. History The Semitic letter Dāleth may have developed from the logogram for a fish or a door. There are many different Egyptian hieroglyphs that might have inspired this. In Semitic, Ancient Greek and Latin, the letter represented ; in the Etruscan alphabet the letter was archaic, but still retained (see letter B). The equivalent Greek letter is Delta, Δ. Architecture The minuscule (lower-case) form of 'd' consists of a lower-story left bowl and a stem ascender. It most likely developed by gradual variations on the majuscule (capital) form 'D', and today now composed as a stem with a full lobe to the right. In handwriting, it was common to start the arc to the left of the vertical stroke, resulting in a serif at the top of the arc. This serif w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Post-perovskite
Post-perovskite (pPv) is a high-pressure phase of magnesium silicate (MgSiO3). It is composed of the prime oxide constituents of the Earth's rocky mantle (MgO and SiO2), and its pressure and temperature for stability imply that it is likely to occur in portions of the lowermost few hundred km of Earth's mantle. The post-perovskite phase has implications for the ''D''′′ layer, which influences the convective mixing in the mantle responsible for plate tectonics. Post-perovskite has the same crystal structure as the synthetic solid compound CaIrO3, and is often referred to as the "CaIrO3-type phase of MgSiO3" in the literature. The crystal system of post-perovskite is orthorhombic, its space group is ''Cmcm'', and its structure is a stacked SiO6-octahedral sheet along the ''b'' axis. The name "post-perovskite" derives from silicate perovskite, the stable phase of MgSiO3 throughout most of Earth's mantle, which has the perovskite structure. The prefix "post-" refers to the fact t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bridgmanite
Silicate perovskite is either (the magnesium end-member is called bridgmanite) or (calcium silicate known as davemaoite) when arranged in a perovskite structure. Silicate perovskites are not stable at Earth's surface, and mainly exist in the lower part of Earth's mantle, between about depth. They are thought to form the main mineral phases, together with ferropericlase. Discovery The existence of silicate perovskite in the mantle was first suggested in 1962, and both and had been synthesized experimentally before 1975. By the late 1970s, it had been proposed that the seismic discontinuity at about 660 km in the mantle represented a change from spinel structure minerals with an olivine composition to silicate perovskite with ferropericlase. Natural silicate perovskite was discovered in the heavily shocked Tenham meteorite. In 2014, the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA) approved the na ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lower Mantle (Earth)
The lower mantle, historically also known as the mesosphere, represents approximately 56% of Earth's total volume, and is the region from 660 to 2900 km below Earth's surface; between the transition zone and the outer core. The preliminary reference Earth model (PREM) separates the lower mantle into three sections, the uppermost (660–770 km), mid-lower mantle (770–2700 km), and the D layer (2700–2900 km). Pressure and temperature in the lower mantle range from 24–127 GPa and 1900–2600 K. It has been proposed that the composition of the lower mantle is pyrolitic, containing three major phases of bridgmanite, ferropericlase, and calcium-silicate perovskite. The high pressure in the lower mantle has been shown to induce a spin transition of iron-bearing bridgmanite and ferropericlase, which may affect both mantle plume dynamics and lower mantle chemistry. The upper boundary is defined by the sharp increase in seismic wave velocities and density at a d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ringwoodite
Ringwoodite is a high-pressure phase of Mg2SiO4 (magnesium silicate) formed at high temperatures and pressures of the Earth's mantle between depth. It may also contain iron and hydrogen. It is polymorphous with the olivine phase forsterite (a magnesium iron silicate). Ringwoodite is notable for being able to contain hydroxide ions (oxygen and hydrogen atoms bound together) within its structure. In this case two hydroxide ions usually take the place of a magnesium ion and two oxide ions. Combined with evidence of its occurrence deep in the Earth's mantle, this suggests that there is from one to three times the world ocean's equivalent of water in the mantle transition zone from 410 to 660 km deep. This mineral was first identified in the Tenham meteorite in 1969, and is inferred to be present in large quantities in the Earth's mantle. Ringwoodite was named after the Australian earth scientist Ted Ringwood (1930–1993), who studied polymorphic phase transitions in the co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wadsleyite
Wadsleyite is an orthorhombic mineral with the formula β-(Mg,Fe)2SiO4. It was first found in nature in the Peace River meteorite from Alberta, Canada. It is formed by a phase transformation from olivine (α-(Mg,Fe)2SiO4) under increasing pressure and eventually transforms into spinel-structured ringwoodite (γ-(Mg,Fe)2SiO4) as pressure increases further. The structure can take up a limited amount of other bivalent cations instead of magnesium, but contrary to the α and γ structures, a β structure with the sum formula Fe2SiO4 is not thermodynamically stable. Its cell parameters are approximately a = 5.7 Å, b = 11.71 Å and c = 8.24 Å. Wadsleyite is found to be stable in the upper part of the Transition Zone of the Earth's mantle between in depth. Because of oxygen atoms not bound to silicon in the Si2O7 groups of wadsleyite, it leaves some oxygen atoms insufficiently bonded. Thus, these oxygens are hydrated easily, allowing for high concentrations of hydroge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mantle Transition Zone
The transition zone is part of the Earth's mantle, and is located between the lower mantle and the upper mantle, between a depth of 410 and 660 km (250 to 400 mi). The Earth's mantle, including the transition zone, consists primarily of peridotite, an ultramafic igneous rock. The mantle was divided into the upper mantle, transition zone, and lower mantle as a result of sudden seismic-velocity discontinuities at depths of 410 and 660 km (250 to 400 mi). This is thought to occur as a result of rearrangement of grains in olivine (which constitutes a large portion of peridotite) at a depth of 410 km, to form a denser crystal structure as a result of the increase in pressure with increasing depth. Below a depth of 660 km, evidence suggests due to pressure changes ringwoodite minerals change into two new denser phases, bridgmanite and periclase. This can be seen using body waves from earthquakes, which are converted, reflected or refracted at the boundar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tibetan Plateau
The Tibetan Plateau (, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau () or as the Himalayan Plateau in India, is a vast elevated plateau located at the intersection of Central, South and East Asia covering most of the Tibet Autonomous Region, most of Qinghai, western half of Sichuan, Southern Gansu provinces in Western China, southern Xinjiang, Bhutan, the Indian regions of Ladakh and Lahaul and Spiti (Himachal Pradesh) as well as Gilgit-Baltistan in Pakistan, northwestern Nepal, eastern Tajikistan and southern Kyrgyzstan. It stretches approximately north to south and east to west. It is the world's highest and largest plateau above sea level, with an area of (about five times the size of Metropolitan France). With an average elevation exceeding and being surrounded by imposing mountain ranges that harbor the world's two highest summits, Mount Everest and K2, the Tibetan Plateau is often referred to as "the Roof of the World". The Tibetan Plateau ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oceanic Crust
Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the rigid uppermost layer of the mantle. The crust and the rigid upper mantle layer together constitute oceanic lithosphere. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick; however, it is denser, having a mean density of about 3.0 grams per cubic centimeter as opposed to continental crust which has a density of about 2.7 grams per cubic centimeter. The crust uppermost is the result of the cooling of magma derived from mantle material below the plate. The magma is injected into the spreading center, which consists mainly of a partly solidified crystal mush derived from earlier ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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