Talk:Lithosphere

message: 168.212.92.5 17:06, 21 September 2006 (UTC)
replies: text: Geology by Chernicoff & Whitney, 4th ed., page 386, states that average thickness for oceanic lithosphere (=crust plus upper mantle) is 70 km and for continental lithosphere 150 km. You are right that the lithosphere is defined as the brittle topmost layer, but the depth at which this changes to plastic depends on the material present, and this is different in the continental vs. the oceanic setting. The density of the material (which affects pressure) as well as its relationship between temperature and plasticity both play a role.AxelBoldt 00:56, 24 May 2006 (UTC)
thread_title:  Older comments 

message: The Earth's hydrosphere consists chiefly of oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters. The average depth of the oceans is 3,794 m (12,447 ft), more than five times the average height of the continents. The mass of the oceans is approximately 1.35 × 1018 tonnes, or about 1/4400 of the total mass of the Earth (ranges reported: 1.347 × 1021 to 1.4 × 1021 kg.[1] )
The abundance of water on Earth is a unique feature that distinguishes our "Blue Planet" from others in the solar system. Approximately 70.8 percent (97% of it being sea water and 3% fresh water[2]) of the Earth is covered by water and only 29.2 percent is landmass. Earth's solar orbit, vulcanism, gravity, greenhouse effect, magnetic field and oxygen-rich atmosphere seem to combine to make Earth a water planet.
Earth is actually beyond the outer edge of the orbits which would be warm enough to form liquid water. Without some form of a greenhouse effect, Earth's water would freeze. Paleontological evidence indicates that at one point after blue-green bacteria (Cyanobacteria) had colonized the oceans, the greenhouse effect failed, and Earth's oceans may have completely frozen over for 10 to 100 million years in what is called a snowball Earth event.
On other planets, such as Venus, gaseous water is destroyed (cracked) by solar ultraviolet radiation, and the hydrogen is ionized and blown away by the solar wind. This effect is slow, but inexorable. This is one hypothesis explaining why Venus has no water. Without hydrogen, the oxygen interacts with the surface and is bound up in solid minerals.
In the Earth's atmosphere, a tenuous layer of ozone within the stratosphere absorbs most of this energetic ultraviolet radiation high in the atmosphere, reducing the cracking effect. The ozone, too, can only be produced in an atmosphere with a large amount of free diatomic oxygen, and so also is dependent on the biosphere (plants). The magnetosphere also shields the ionosphere from direct scouring by the solar wind.
Finally, volcanism continuously emits water vapor from the interior. Earth's plate tectonics recycle carbon and water as limestone rocks are subducted into the mantle and volcanically released as gaseous carbon dioxide and steam. It is estimated that the minerals in the mantle may contain as much as 10 times the water as in all of the current oceans, though most of this trapped water will never be released.
The water cycle describes the methods of transport for water in the hydrosphere. This cycle includes water beneath the Earth's surface and in rocks (lithosphere), the water in plants and animals (biosphere), the water covering the surface of the planet in liquid and solid forms, and the water in the atmosphere in the form of water vapor, clouds, and precipitation. Movement of water within the hydrosphere is described by the hydrologic cycle. It is easy to see this motion in rivers and streams, but it is harder to tell that there is this motion in lakes and ponds.
The water in the oceans moves as it is of different temperature and salinity on different locations. Surface waters are also moved by winds, giving rise to surface ocean currents. Warm water is lighter or less dense than cold water which is more dense or heavier and salty water is also more dense than fresh water. The combination of the water's temperature and salinity determines whether it rises to the surface, sinks to the bottom, or stays at some intermediate depth.
Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass. The gases are attracted by the gravity of the body, and held fast if gravity is sufficient and the atmosphere's temperature is low. Some planets consist mainly of various gases, and thus have very deep atmospheres (see gas giants).
Earth, Venus, and Mars have atmospheres that envelop their surfaces, as do three of the satellites of the outer planets: Titan, Enceladus (moons of Saturn), and Triton (a moon of Neptune). In addition, the giant planets of the outer solar system - Jupiter, Saturn, Uranus, and Neptune - are composed predominantly of gases. Other bodies in the solar system possess extremely thin atmospheres. Such bodies are the Moon (sodium gas), Mercury (sodium gas), Europa (oxygen) and Io (sulfur). The dwarf planet Pluto also has an envelope of gas as it approaches close to the Sun, but these gases are frozen for most of its orbit.
The Earth's atmosphere consists, from the ground up, of the Troposphere (which includes the planetary boundary layer or peplosphere as lowest layer), Stratosphere, Mesosphere, Ionosphere (or Thermosphere), Exosphere and the Magnetosphere.
Initial atmospheric makeup is generally related to the chemistry and temperature of the local solar nebula during planetary formation and the subsequent escape of interior gases. These original atmospheres underwent much evolution over time, with the varying properties of each planet resulting in very different outcomes.
Surface gravity, the force that holds down an atmosphere, differs significantly among the planets. For example, the large gravitational force of the giant planet Jupiter is able to retain light gases such as hydrogen and helium that escape from lower gravity objects. Second, the distance from the sun determines the energy available to heat atmospheric gas to the point where its molecules' thermal motion exceed the planet's escape velocity, the speed at which gas molecules overcome a planet's gravitational grasp. Thus, the distant and cold Titan, Triton, and Pluto are able to retain their atmospheres despite relatively low gravities.
Since a gas at any particular temperature will have molecules moving at a wide range of velocities, there will almost always be some slow leakage of gas into space. Lighter molecules move faster than heavier ones with the same thermal kinetic energy, and so gases of low molecular weight are lost more rapidly than those of high molecular weight. It is thought that Venus and Mars may have both lost much of their water when, after being photodissociated into hydrogen and oxygen by solar ultraviolet, the hydrogen escaped. Earth's magnetic field helps to prevent this, as the solar wind greatly enhances the escape of hydrogen.
Other mechanisms that can cause atmosphere depletion are solar wind-induced sputtering, impact erosion, weathering, and sequestration—sometimes referred to as "freezing out"—into the regolith and polar caps.
Moreover, on Earth, atmospheric composition is largely governed by the by-products of the very life that it sustains.
Interstellar planets, theoretically, may also retain thick atmospheres.
The lithosphere (from the Greek for "rocky" sphere) is the solid outermost shell of a rocky planet. On the Earth, the lithosphere includes the crust and the uppermost mantle which is joined to the crust across the Mohorovicic discontinuity. Lithosphere is underlain by asthenosphere, the weaker, hotter, and deeper part of the upper mantle. The base of the lithosphere-asthenosphere boundary corresponds approximately to the depth of the melting temperature in the mantle. 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.
The concept of the lithosphere as Earth’s strong outer layer was developed by Barrell, who wrote a series of papers introducing the concept (Barrell 1914a-c). The concept was based on the presence of significant gravity anomalies over continental crust, from which he inferred that there must exist a strong upper layer (which he called the lithosphere) above a weaker layer which could flow (which he called the asthenosphere). These ideas were enlarged by Daly (1940), and have been broadly accepted by geologists and geophysicists. Although these ideas about lithosphere and asthenosphere were developed long before plate tectonic theory was articulated in the 1960's, the concepts that strong lithosphere exists and that this rests on weak lithosphere are essential to that theory.
The division of Earth's outer layers into lithosphere and asthenosphere should not be confused with the chemical subdivision of the outer Earth into mantle, and crust. All crust is in the lithosphere, but lithosphere generally contains more mantle than crust.
There are two types of lithosphere:
Oceanic lithosphere, which is associated with Oceanic crust 
Continental lithosphere, which is associated with Continental crust 
Oceanic lithosphere is typically about 50-100 km thick (but beneath the mid-ocean ridges is no thicker than the crust), while continental lithosphere is about 150 km thick, consisting ~50 km of crust and 100km or more of uppermost mantle. Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle and is denser than continental lithosphere, for which the mantle is associated with crust made of felsic rocks. The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the Moho discontinuity. Oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle, and causes the oceanic lithosphere to become increasingly dense with age. Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years, but after this becomes increasingly denser than asthenosphere. The gravitational instability of mature oceanic lithosphere has the effect that at subduction zones the oceanic lithosphere invariably sinks underneath the overriding lithosphere, which can be oceanic or continental. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones. As a result, oceanic lithosphere is much younger than continental lithosphere: the oldest oceanic lithosphere is about 170 million years old, while parts of the continental lithosphere are billions of years old.
Another distinguishing characteristic of the lithosphere is its flow properties. Under the influence of the low-intensity, long-term stresses that drive plate tectonic motions, the lithosphere responds essentially as a rigid shell and thus deforms primarily through brittle failure, whereas the asthenosphere (the layer of the mantle below the lithosphere) is heat-softened and accommodates strain through plastic deformation.
Geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths brought up in kimberlite and other volcanic pipes —The preceding unsigned comment was added by 70.186.162.149 (talk) 00:10, 31 January 2007 (UTC)
thread_title:  ME AND MY EARTH 

message: No one ever got their Moho working —The preceding unsigned comment was added by Zyzzy2 (talk • contribs) 04:32, 22 April 2007 (UTC)
thread_title:  Moho not mojo 

message: Oh yes the oceanic and continental lithospheres are quite different, and surly the crusts are different but the mantles are distinct as well.  Sub-oceanis mantle lithosphere (SOML) is distinctly younger and thinner than sub-continental continental mantle lithosphere (SCML).  SCML shows isotopic characteristics of ancient enrichments and depletions —The preceding unsigned comment was added by Zyzzy2 (talk • contribs) 04:39, 22 April 2007 (UTC)
thread_title:  2 types of lithosphere 

message: This figure is confusing because it doesn't even show the lithosphere.  Why confuse people unnecessarily? Zyzzy2 16:23, 26 May 2007 (UTC)
thread_title:  Second Figure is not useful and should be replaced or at least deleted

message: It's unclear in the article whether the Lithosphere is a real proven FACT, or merely part of a larger THEORY. As tectonic plates are described as a theory, there should be a more obvious connection to the theoretical nature of the lithosphere. It's true that people are expected to approach Wikipedia with at least some degree of caution, but let's make it clear for the audience. 
Unless, of course, I am somehow wrong... As far as I know, the reason plate tectonics are THEORY is because nobody has actually drilled to the center of the earth to take samples. In fact, I don't think we've been able to get very deep at all. Certainly we can call the "top" layer lithosphere if we want, but the article expands on that to include where it places in tectonics, mixing any possible known facts about the lithosphere with theory. - Commandur (talk) 10:03, 19 January 2010 (UTC)
replies: text: The lithosphere is something that is observed. We may not have drilled it to get samples but we have a lot of remote sensed data especially seismic data, on which the lithosphere is well 'imaged' because its base shows up as a marked change in S-wave velocity. The concept of the lithosphere is much older than the theory of Plate tectonics, it was developed about a hundred years ago, so stands on its own. Mikenorton (talk) 18:00, 19 January 2010 (UTC)

text: I hope there is no implication that a 'theory' is an unproved concept.  This would be quite wrong and it is not the meaning of the word in science.  As stated the Lithosphere is an Earth Science model to explain the geophysical data (and the petrological data from magmas originating at depth).  This data and the model were used in Geodynamics to make predictions that match both geophysical and topographic data of such things as Island Arcs, Subduction zones, Ocean Ridges, etc.  So it is accepted that it is the best model as it fits the 'facts' extremely well.  —Preceding unsigned comment added by Physics Sensei (talk • contribs) 23:44, 14 May 2010 (UTC)

text: In astronomy, the geocentric model (also known as geocentrism, or the Ptolemaic system), is the theory, that the Earth is the center of the universe, and that all other objects orbit around it. So I guess geocentricism is not an unproved concept, since it was embraced for like 1500 years. DasV (talk) 19:59, 14 March 2011 (UTC)
thread_title:  Lithosphere part of Tectonic Plate THEORY 

message: There is something wrong with the description of the formula under oceanic lithosphere.  In the equation the symbol for thermal diffusivity is kappa but in the text it looks like chi, even though in the text for editing the symbol is given as kappa.  I don't know how to fix it.  —Preceding unsigned comment added by Earthophile (talk • contribs) 00:53, 11 July 2010 (UTC)
thread_title:  Formula under oceanic lithosphere 

message: "Lithosphere" has the potential to become a really great article, but it is currently missing a few key topics. The article would benefit from discussions of the effective elastic thickness and how it relates to lithospheric thickness (Burov and Diament, 1995), rheological models of the lithosphere (i.e., yield strength envelopes)(Goetze and Evans, 1979), and the observation that the equation given for lithospheric thickness does not work for lithosphere older than ~80 Ma, possibly due to small-scale convection (Parsons and McKenzie, 1978).
However, I think this article would benefit most from a discussion of the different ways in which the base of the lithosphere is defined. Right now the article suggests that the base of the lithosphere is defined as the brittle-ductile transition (BDT) in olivine, following the mechanical-boundary layer definition of Parsons and McKenzie (1978). However, several other definitions exist including 1) the crust and portion of the mantle which mainly transports heat through conduction rather than convection (i.e., a thermal boundary layer), 2) a rheological boundary defined by compositional differences (e.g., water and/or melt content; this is becoming increasingly well received and should be mentioned), and 3) the seismically fast, elastically anisotropic lid (i.e., seismic lithosphere). An excellent review is given by Fischer et al. (Annual Reviews of Earth and Planetary Sciences, 2010).
Although the definition currently provided is worth mentioning, statements such as "the lithosphere remains rigid for very long periods of geologic time in which it deforms elastically and through brittle failure" reflect the outdated perspective of the article as written.  — Preceding unsigned comment added by Larhansen (talk • contribs) 16:44, 10 April 2011 (UTC)
thread_title:  Definition of lithosphere asthenosphere boundary 

message: I was hoping for a list of the most common elements and their concentrations in the lithosphere. I was reading an old geology text (c. 1950's) that listed Oxygen and Silicon as the most common, and gave percentages. However, I was unclear if those were proportions by mass, or by volume. I was hoping Wiki could help me out. Perhaps someone could add that information for future readers.  — Preceding unsigned comment added by 2602:30A:C08C:A6F0:21C:B3FF:FEC3:2572 (talk) 13:19, 19 February 2014 (UTC)
replies: text: Typically given as mass percent, see Crust (geology)#Composition. Vsmith (talk) 13:39, 19 February 2014 (UTC)
thread_title: Mineral content?

message: I've always thought of "rheology" as encompassing fluid flow, plastic deformation, elasticity, and even brittle failure. As a student, I used this book by Ranalli:
, where all of these concepts are discussed in the context of the Earth. Yet, when I visit the wikipage Rheology the focus there is on fluid flow and plasticity, not on elasticity and brittleness. Any thoughts on this? Isambard Kingdom (talk) 15:32, 11 July 2015 (UTC)
replies: text: Strictly, flow is what it's about. However, materials show a wide range of behaviour including some elasticity - Bingham plasticity is one type of behaviour that is sometimes used to describe how the lithosphere deforms. More generally the term rheid gets used for the typically time dependent behaviour of rocks, although less often than perhaps it should. I think that earth scientists use rheology in a slightly broader sense than engineers. Mikenorton (talk) 16:16, 11 July 2015 (UTC)
thread_title:  Rheology 

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