On the fate of water in the formation of rocky planets

2021 ◽  
Author(s):  
Lindy Elkins-Tanton ◽  
Jenny Suckale ◽  
Sonia Tikoo
Keyword(s):  
Water Content ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Plate Tectonics ◽  
Solidus Temperature ◽  
Magma Ocean ◽  
Excess Water ◽  
Low Degree ◽  
Giant Impacts ◽  
Rocky Planets

<p>Rocky planets go through at least one and likely multiple magma ocean stages, produced by the giant impacts of accretion. Planetary data and models show that giant impacts do not dehydrate either the mantle or the atmosphere of their target planets. The magma ocean liquid consists of melted target material and melted impactor, and so will be dominated by silicate melt, and also contain dissolved volatiles including water, carbon, and sulfur compounds.</p><p>As the magma ocean cools and solidifies, water and other volatiles will be incorporated into the nominally anhydrous mantle phases up to their saturation limits, and will otherwise be enriched in the remaining, evolving magma ocean liquids. The water content of the resulting cumulate mantle is therefore the sum of the traces in the mineral grains, and any water in trapped interstitial liquids. That trapped liquid fraction may in fact be by far the largest contributor to the cumulate water budget.</p><p>The water and other dissolved volatiles in the evolving liquids may quickly reach the saturation limit of magmas near the surface, where pressure is low, but degassing the magma ocean is likely more difficult than has been assumed in some of our models. To degas into the atmosphere, the gases must exsolve from the liquid and form bubbles, and those bubbles must be able to rise quickly enough to avoid being dragged down by convection and re-dissolved at higher pressures. If bubbles are buoyant enough (that is, large enough) to decouple from flow and rise, then they are also dynamically unstable and liable to be torn into smaller bubbles and re-entrained. This conundrum led to the hypothesis that volatiles do not significantly degas until a high level of supersaturation is reached, and the bubbles form a buoyant layer and rise in diapirs in a continuum dynamics sense. This late degassing would have the twin effects of increasing the water content of the cumulates, and of speeding up cooling and solidification of the planet.</p><p>Once the mantle is solidified, the timeclock until the start of plate tectonics begins. Modern plate tectonics is thought to rely on water to lower the viscosity of the asthenosphere, but plate tectonics is also thought to be the process by which water is brought into the mantle. Magma ocean solidification, however, offers two relevant processes. First, following solidification the cumulate mantle is gravitationally unstable and overturns to stability, carrying water-bearing minerals from the upper mantle through the transition zone and into the lower mantle. Upon converting to lower-mantle phases, these minerals will release their excess water, since lower mantle phases have lower saturation limits, thus fluxing the upper mantle with water. Second, the mantle will be near its solidus temperature still, and thus its viscosity will be naturally low. When fluxed with excess water, the upper mantle would be expected to form a low degree melt, which if voluminous enough with rise to help form the earliest crust, and if of very low degree, will further reduce the viscosity of the asthenosphere.</p>

scholarly journals The fate of water within Earth and super-Earths and implications for plate tectonics

2017 ◽  
Vol 375 (2094) ◽  
pp. 20150394 ◽  
Author(s):  
Sonia M. Tikoo ◽  
Linda T. Elkins-Tanton
Keyword(s):  
Upper Mantle ◽  
Plate Tectonics ◽  
Extrasolar Planets ◽  
Internal Heat ◽  
Magma Ocean ◽  
Nominally Anhydrous Minerals ◽  
The Earth ◽  
Giant Impacts ◽  
Crystallographic Defects

The Earth is likely to have acquired most of its water during accretion. Internal heat of planetesimals by short-lived radioisotopes would have caused some water loss, but impacts into planetesimals were insufficiently energetic to produce further drying. Water is thought to be critical for the development of plate tectonics, because it lowers viscosities in the asthenosphere, enabling subduction. The following issue persists: if water is necessary for plate tectonics, but subduction itself hydrates the upper mantle, how is the upper mantle initially hydrated? The giant impacts of late accretion created magma lakes and oceans, which degassed during solidification to produce a heavy atmosphere. However, some water would have remained in the mantle, trapped within crystallographic defects in nominally anhydrous minerals. In this paper, we present models demonstrating that processes associated with magma ocean solidification and overturn may segregate sufficient quantities of water within the upper mantle to induce partial melting and produce a damp asthenosphere, thereby facilitating plate tectonics and, in turn, the habitability of Earth-like extrasolar planets. This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’.

3. Minerals and the interior of the Earth

2014 ◽  
Author(s):  
David Vaughan
Keyword(s):  
Upper Mantle ◽  
Lower Mantle ◽  
Plate Tectonics ◽  
Inner Core ◽  
Indirect Evidence ◽  
Outer Core ◽  
The Earth ◽  
Granite Formation ◽  
Temperature And Pressure

‘Minerals and the interior of the Earth’ looks at the role of minerals in plate tectonics during the processes of crystallization and melting. The size and range of minerals formed are dependent on the temperature and pressure of the magma during its movement through the crust. The evolution of the continental crust also involves granite formation and processes of metamorphism. Our understanding of the interior of the Earth is based on indirect evidence, mainly the study of earthquake waves. The Earth consists of concentric shells: a solid inner core; liquid outer core; a solid mantle divided into a lower mantle, a transition zone, and an upper mantle; and then the outer rigid lithosphere.

scholarly journals Mantle Evolution of Asia Inferred from Pb Isotopic Signatures of Sources for Late Phanerozoic Volcanic Rocks

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 739
Author(s):  
Sergei Rasskazov ◽  
Irina Chuvashova ◽  
Tatyana Yasnygina ◽  
Elena Saranina
Keyword(s):  
Upper Mantle ◽  
Lower Mantle ◽  
Volcanic Rocks ◽  
Solid Core ◽  
Magma Ocean ◽  
Low Velocity ◽  
Isotopic Signatures ◽  
Mantle Evolution ◽  
Mantle Sources

We present a systematic study of Pb isotope ages obtained from sources of the late Phanerozoic volcanic rocks from unstable Asia and also volcanic rocks and kimberlites from stable regions of the Siberian and Indian paleocontinents. In the mantle sources, we have recorded events of the Early, Middle, and Late epochs of the Earth’s evolution. Evidence on the Early epoch are preserved in sources of the protolithosphere and viscous lower protomantle likely generated from the Hadean magma ocean about 4.51 and 4.44 Ga and in sources of the viscous upper mantle that acquired low µ and elevated µ (LOMU and ELMU) signatures in the early Archean (4.0–3.7 Ga). The Middle and Late epochs are denoted by sources of the viscous upper mantle that was generated, respectively, in the late Archean-Paleoproterozoic (2.9–2.6 Ga and 2.0–1.8 Ga) and in the Neoproterozoic-late Phanerozoic (0.7–0.6 Ga and < 0.25 Ga). Our results show the specific role of the mantle beneath unstable Asia in terms of globally varied µ signatures and the same mantle epochs in sources of the late Phanerozoic volcanic rocks and kimberlites from stable regions of the Siberian and Indian paleocontinents, but with high μ (HIMU) signatures that are distributed worldwide and explained by sulfide sequestration of Pb from the mantle to the core. We refer the LOMU-ELMU mantle sources to the Asian high-velocity lower mantle domain and propose that the HIMU generating processes were focused mainly in the South Pacific and African low-velocity lower mantle domains in the Middle Mantle Epoch of the Earth’s evolution due to influence of the unbalanced solid core.

How does volcanic outgassing differ on geological time scales between planets with and without plate tectonics?

2021 ◽  
Author(s):  
Lena Noack
Keyword(s):  
Plate Tectonics ◽  
Plate Boundaries ◽  
Magma Ocean ◽  
Geological Time ◽  
Molten Material ◽  
Liquid Form ◽  
Formation Stage ◽  
Harmful Radiation ◽  
Rocky Planets ◽  
Volcanic Outgassing

&lt;div&gt;One of the main factors to assess the possible habitability of a rocky planet (either in or beyond our solar system) is its capability to maintain an atmosphere that allows for moderate temperatures at the surface and would allow water to occur in a liquid form, and that can help shield surface life from harmful radiation.&lt;/div&gt; &lt;div&gt;The existence of an atmosphere depends on several factors - possible accretion from the nebula and catastrophic degassing from the crystallizing magma ocean during planet formation, later delivery of volatiles via comets, sinks of atmosphere gases to the surface or to space, and last, but definitely not least, volcanic release of volatiles from the mantle that where stored in the planet's interior during its formation stage.&lt;/div&gt; &lt;div&gt;For planets of masses not too different from Earth, volcanic degassing plays a major role for the question if the planet could have an atmosphere. Lower-mass planets might not be able to keep an atmosphere but loose it entirely to space, and much more massive super-Earth planets will likely keep the primordial, catastrophically outgassed atmosphere during magma ocean crystallization, and may never be habitable at their surface due to a thick atmosphere rather comparable to Venus. The &quot;Goldilocks zone&quot; for potentially habitable rocky planets is therefore limited to a range from&amp;#160;above Mars' mass to a few Earth masses. However, planets of a few Earth masses may not be able to efficiently outgas volcanic gases, if they are in a stagnant-lid regime. This may be different, though, for planets experiencing plate tectonics like Earth, where hot, molten material reaches the surface at plate boundaries and may therefore build up or replenish an atmosphere. The work presented here compares the efficiency of interior volatile depletion and degassing to the surface for rocky planets of different size and composition, either in the stagnant-lid or in the plate-tectonics regime.&lt;/div&gt;

scholarly journals Direct imaging of molten protoplanets in nearby young stellar associations

2019 ◽  
Vol 621 ◽  
pp. A125 ◽  
Author(s):  
Irene Bonati ◽  
Tim Lichtenberg ◽  
Dan J. Bower ◽  
Miles L. Timpe ◽  
Sascha P. Quanz
Keyword(s):  
Planet Formation ◽  
Magma Ocean ◽  
Direct Imaging ◽  
Origin And Evolution ◽  
Giant Impacts ◽  
Formation And Evolution ◽  
Magma Oceans ◽  
Rocky Planets ◽  
Stellar Associations

During their formation and early evolution, rocky planets undergo multiple global melting events due to accretionary collisions with other protoplanets. The detection and characterization of their post-collision afterglows (magma oceans) can yield important clues about the origin and evolution of the solar and extrasolar planet population. Here, we quantitatively assess the observational prospects to detect the radiative signature of forming planets covered by such collision-induced magma oceans in nearby young stellar associations with future direct imaging facilities. We have compared performance estimates for near- and mid-infrared instruments to be installed at ESO’s Extremely Large Telescope (ELT), and a potential space-based mission called Large Interferometer for Exoplanets (LIFE). We modelled the frequency and timing of energetic collisions using N-body models of planet formation for different stellar types, and determine the cooling of the resulting magma oceans with an insulating atmosphere. We find that the probability of detecting at least one magma ocean planet depends on the observing duration and the distribution of atmospheric properties among rocky protoplanets. However, the prospects for detection significantly increase for young and close stellar targets, which show the highest frequencies of giant impacts. For intensive reconnaissance with a K band (2.2 μm) ELT filter or a 5.6 μm LIFE filter, the β Pictoris, Columba, TW Hydrae, and Tucana-Horologium associations represent promising candidates for detecting a molten protoplanet. Our results motivate the exploration of magma ocean planets using the ELT and underline the importance of space-based direct imaging facilities to investigate and characterize planet formation and evolution in the solar vicinity. Direct imaging of magma oceans will advance our understanding of the early interior, surface and atmospheric properties of terrestrial worlds.

scholarly journals Speculations on the Generation and Movement of Komatiites

2020 ◽  
Vol 61 (7) ◽  
Author(s):  
Dan McKenzie
Keyword(s):  
Boundary Layer ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Thermal Boundary Layer ◽  
Solidus Temperature ◽  
Stable Phase ◽  
Average Temperature ◽  
Low Concentrations ◽  
Greenstone Belts ◽  
Archean Greenstone Belts

Abstract The discovery of komatiites, first in South Africa and then in many other Archean greenstone belts, with MgO concentrations of 20–30% and eruption temperatures of more than ∼1600 °C, showed that some parts of the mantle were hotter in the Archean than they are now. Since their discovery there have been many speculative proposals as to how such magmas can form. At present melt is produced by mantle upwelling, because the solidus temperature gradient of the mantle is steeper than that of isentropic decompression gradient at depths of less than 300 km. In contrast, in the lower half of the upper mantle the solidus gradient is shallower than the isentropic gradient, and, therefore, isentropic upwelling cannot generate melt. At the base of the upper mantle limited melting can occur, either in the thermal boundary layer at the base of the upper mantle, or in the upper part of the lower mantle where the solidus gradient is steeper than the isentropic gradient. In both cases melting can occur at depths of more than 600 km, where Ca perovskite, CaPv, is a stable phase on the solidus. A surprising feature of the partitioning between melt and solid CaPv is that most trace elements are compatible in the solid. Partitioning into CaPv can, therefore, account for the low concentrations of such elements in komatiites. The temperatures required to generate such magmas in plumes need be no more than ∼50 °C above those of Phanerozoic plumes. The presence of komatiites in the Archean, therefore, requires plume temperatures in the first half of the Earth’s history to have been somewhat hotter than they are now, but does not constrain the average temperature of the Archean upper mantle.

scholarly journals Magma oceans as a critical stage in the tectonic development of rocky planets

2018 ◽  
Vol 376 (2132) ◽  
pp. 20180109 ◽  
Author(s):  
Laura Schaefer ◽  
Linda T. Elkins-Tanton
Keyword(s):  
Plate Tectonics ◽  
Magma Ocean ◽  
Stability Issue ◽  
Tectonic Development ◽  
Magma Oceans ◽  
Set Up ◽  
Almost All ◽  
High Degree ◽  
Rocky Planets ◽  
Earth Dynamics

Magma oceans are a common result of the high degree of heating that occurs during planet formation. It is thought that almost all of the large rocky bodies in the Solar System went through at least one magma ocean phase. In this paper, we review some of the ways in which magma ocean models for the Earth, Moon and Mars match present-day observations of mantle reservoirs, internal structure and primordial crusts, and then we present new calculations for the oxidation state of the mantle produced during the magma ocean phase. The crystallization of magma oceans probably leads to a massive mantle overturn that may set up a stably stratified mantle. This may lead to significant delays or total prevention of plate tectonics on some planets. We review recent models that may help alleviate the mantle stability issue and lead to earlier onset of plate tectonics. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics’.

scholarly journals Feedbacks between a non-Newtonian upper mantle, mantle viscosity structure and mantle dynamics

2020 ◽  
Vol 224 (2) ◽  
pp. 961-972
Author(s):  
A G Semple ◽  
A Lenardic
Keyword(s):  
Upper Mantle ◽  
Lower Mantle ◽  
Mantle Convection ◽  
Mantle Flow ◽  
Mantle Dynamics ◽  
Plate Motions ◽  
Low Viscosity ◽  
Mantle Viscosity ◽  
Flow Feature ◽  
Mantle Rheology

SUMMARY Previous studies have shown that a low viscosity upper mantle can impact the wavelength of mantle flow and the balance of plate driving to resisting forces. Those studies assumed that mantle viscosity is independent of mantle flow. We explore the potential that mantle flow is not only influenced by viscosity but can also feedback and alter mantle viscosity structure owing to a non-Newtonian upper-mantle rheology. Our results indicate that the average viscosity of the upper mantle, and viscosity variations within it, are affected by the depth to which a non-Newtonian rheology holds. Changes in the wavelength of mantle flow, that occur when upper-mantle viscosity drops below a critical value, alter flow velocities which, in turn, alter mantle viscosity. Those changes also affect flow profiles in the mantle and the degree to which mantle flow drives the motion of a plate analogue above it. Enhanced upper-mantle flow, due to an increasing degree of non-Newtonian behaviour, decreases the ratio of upper- to lower-mantle viscosity. Whole layer mantle convection is maintained but upper- and lower-mantle flow take on different dynamic forms: fast and concentrated upper-mantle flow; slow and diffuse lower-mantle flow. Collectively, mantle viscosity, mantle flow wavelengths, upper- to lower-mantle velocities and the degree to which the mantle can drive plate motions become connected to one another through coupled feedback loops. Under this view of mantle dynamics, depth-variable mantle viscosity is an emergent flow feature that both affects and is affected by the configuration of mantle and plate flow.

Palmer Amaranth (Amaranthus palmeri) Competition for Water in Cotton

Weed Science ◽  
2015 ◽  
Vol 63 (4) ◽  
pp. 928-935 ◽  
Author(s):  
Sarah T. Berger ◽  
Jason A. Ferrell ◽  
Diane L. Rowland ◽  
Theodore M. Webster
Keyword(s):  
Water Content ◽  
Relative Water Content ◽  
Yield Loss ◽  
Linear Trend ◽  
Palmer Amaranth ◽  
Cotton Production ◽  
Excess Water ◽  
Relative Water ◽  
Competition For Light ◽  
Daily Water

Palmer amaranth is a troublesome weed in cotton production. Yield losses of 65% have been reported from season-long Palmer amaranth competition with cotton. To determine whether water is a factor in this system, experiments were conduced in 2011, 2012, and 2013 in Citra, FL, and in Tifton, GA. In 2011, infrequent rainfall lead to drought stress. The presence of Palmer amaranth resulted in decreased soil relative water content up to 1 m in depth. Cotton stomatal conductance (gs) was reduced up to 1.8 m from a Palmer amaranth plant. In 2012 and 2013 higher than average rainfall resulted in excess water throughout the growing season. In this situation, no differences were found in soil relative water content or cottongsas a function of proximity to Palmer amaranth. A positive linear trend was found in cotton photosynthesis and yield; each parameter increased as distance from Palmer amaranth increased. Even in these well-watered conditions, daily water use of Palmer amaranth was considerably higher than that of cotton, at 1.2 and 0.49 g H20 cm−2d−1, respectively. Although Palmer amaranth removed more water from the soil profile, rainfall was adequate to replenish the profile in 2 of the 3 yr of this study. However, yield loss due to Palmer amaranth was still observed despite no change ings, indicating other factors, such as competition for light or response to neighboring plants during development, are driving yield loss.

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