TRUE or FALSE: The mantle is relatively rigid compared to the asthenosphere because the pressures are so low. A. True B. False?
yes!
What is the lithosphere and asthenosphere?
For the best answers, search on this site https://shorturl.im/ayjXe On the Earth, the lithosphere includes the crust and the uppermost mantle which is joined to the crust across the mantle. The lithosphere is underlain by the asthenosphere, the weaker, hotter, and deeper part of the upper mantle. The boundary between the lithosphere and the underlying asthenosphere is defined by a difference in response to stress: the lithosphere remains rigid for long periods of geologic time, whereas the asthenosphere flows much more readily. As the conductively cooling surface layer of the Earth's convection system, the lithosphere thickens over time. It is fragmented into tectonic plates (shown in the picture), which move independently relative to one another. This movement of lithospheric plates is described as plate tectonics. This is when plates move horizontally across the Earth's surface and the continents change their relative positions. If the core cooled enough for the mantle to solidify, the tectonic plates would stop moving because they move on the semi-liquid mantle.
How much pressure is on the asthenosphere?
The asthenosphere (from Greek asthenēs 'weak' + sphere) is the mechanically weak ductily-deforming region of the upper mantle of the Earth. It lies below the lithosphere, at depths between 100 and 200 km (~ 62 and 124 miles) below the surface, but perhaps extending as deep as 400 km (~ 249 miles). The asthenosphere is a portion of the upper mantle just below the lithosphere that is involved in plate movements and isostatic adjustments. In spite of its heat, pressures keep it plastic, and it has a relatively low density. Seismic waves pass relatively slowly through the asthenosphere, compared to the overlying lithospheric mantle, thus it has been called the low-velocity zone. This was the observation that originally alerted seismologists to its presence and gave some information about its physical properties, as the speed of seismic waves decreases with decreasing rigidity.
Below the crust is the mantle, a dense, hot layer of semi-solid rock approximately 2,900 km thick. The mantle, which contains more iron, magnesium, and calcium than the crust, is hotter and denser because temperature and pressure inside the Earth increase with depth. As a comparison, the mantle might be thought of as the white of a boiled egg. At the center of the Earth lies the core, which is nearly twice as dense as the mantle because its composition is metallic (iron-nickel alloy) rather than stony. Unlike the yolk of an egg, however, the Earth's core is actually made up of two distinct parts: a 2,200 km-thick liquid outer core and a 1,250 km-thick solid inner core. As the Earth rotates, the liquid outer core spins, creating the Earth's magnetic field.Not surprisingly, the Earth's internal structure influences plate tectonics. The upper part of the mantle is cooler and more rigid than the deep mantle; in many ways, it behaves like the overlying crust. Together they form a rigid layer of rock called the lithosphere (The solid part of the earth consisting of the crust and outer mantle). The lithosphere tends to be thinnest under the oceans and in volcanically active continental areas, such as the Western United States. Averaging at least 80 km in thickness over much of the Earth, the lithosphere has been broken up into the moving plates that contain the world's continents and oceans. Scientists believe that below the lithosphere is a relatively narrow, mobile zone in the mantle called the asthenosphere (The lower layer of the crust). This zone is composed of hot, semi-solid material, which can soften and flow after being subjected to high temperature and pressure over geologic time. The rigid lithosphere is thought to "float" or move about on the slowly flowing asthenosphere.
An earthquake (EQ) is not caused by the movement of tectonic plate, they are caused by excess pressure in the crust, and upper mantle. And if tectonic plates are involved, they are moved by pressure. The theory of movement of tectonic plates ca’t be proven, but EQ’s caused by pressure in the crust, and mantle can. There are three types of earthquakes.Voolcanic EQ’s: They are caused when pressure from the lower mantle rises up to the upper mantle, and crust, and push against them.Natural gas well EQ’s: They are caused when the natural gas in a gas well is ignited. The gas explodes, and expand, and push the upper mantle, and crust apart. The explosion can’t be heard, because it takes place underground, but the shock wave (epicenter) can be felt.Fracking, and water injection EQ’s: They are caused when oil companies pump high pressure, and chemical into the crust to remove hydrocarbons, or water injection to get rid of chemical wastewater dur to fracking.In any event, when upwards movement of the ocean flood is pushed upwards by the pressure a Tsunamis will formed. Most Tsunamis form during volcanic EQ’sArtificial EQ’s can be triggered by using the waste water injection process, or by igniting the gas in a natural gas well. Natural gas EQ’s are the strongest of the threeEvidence Connects Quakes to Oil, Natural Gas BoomHow Oil and Gas Disposal Wells Can Cause EarthquakesVolcanic Earthquakes | Pacific Northwest Seismic Network
Long story short - continental crust is thicker because is less dense, and it is less dense because it's composed mostly of quartz and feldspars, both having density around 2.6 g/cm3, whereas oceanic crust is made up by slightly denser Ca feldspar called plagioclase as well as pyroxenes and olivine, both having density above 3 g/dm3. If oceanic crust grows too thick it sinks into underlaying mantle - it's called subduction.And why we have those two major types of crust in the first place? When molten rock, be it huge magma ocean of the early Earth or small intrusion today, starts to crystalize at temperature well above 1000 degree C, first-appearing minerals are those rich in Mg and Fe like olivines - order of crystalization is descibed by Bowen's reaction series. Those minerals, be extracting denser elements, make the remaining magma less dense and richer in Si, Al, K etc., so by establishing a density contrast dense minerals can sink to the bottom of the magma reservoir.
The mantle makes up a large part of the Earth's crust??
the mantle and the crust are different areas of the earth. Your statement is false, although it could be a poorly worded one intended to state that much of the crust is of direct mantle origin. Oceanic crust is dominated by mantle material that has injected into or extruded onto the crustal region via partial melting of the upper mantle. Thus, oceanic crust (until you add sediments) is very similar chemically to upper mantle material. The lower crust of continents is evidently similar (but without the extrusions, only intrusions are possible, of course). The mantle is not mostly molten, either, which is a very common error. It is "plastic" in behavior, but it is almost entirely solid in state.
The lithosphere is the solid, outer part of the Earth, extending to a depth of about 100 kilometers (62 miles). The lithosphere includes both the crust and the brittle upper portion of the mantle. The lithosphere is both the coolest and the most rigid of Earth’s layers.The most well-known feature associated with Earth’s lithosphere is tectonic activity. Tectonic activity describes the interaction of the huge slabs of lithosphere called tectonic plates. The lithosphere is divided into 15 major tectonic plates: the North American, Caribbean, South American, Scotia, Antarctic, Eurasian, Arabian, African, Indian, Philippine, Australian, Pacific, Juan de Fuca, Cocos, and Nazca.The division in the lithosphere between the crust and the mantle is called the Mohorovicic discontinuity, or simply the Moho. The Moho does not exist at a uniform depth, because not all regions of Earth are equally balanced in isostatic equilibrium. Isostasy describes the physical, chemical, and mechanical differences that allow the crust to “float” on the sometimes more malleable mantle. The Moho is found at about 8 kilometers (5 miles) beneath the ocean and about 32 kilometers (20 miles) beneath continents.Different types of rocks distinguish lithospheric crust and mantle. Lithospheric crust is characterized by gneiss (continental crust) and gabbro (oceanic crust). Below the Moho, the mantle is characterized by peridotite, a rock mostly made up of the minerals olivine and pyroxene.Source: mantle