Minimum heat flow from the core and thermal evolution of the Earth

2020 ◽  
Vol 305 ◽  
pp. 106457
Author(s):  
V. Patočka ◽  
O. Šrámek ◽  
N. Tosi
Keyword(s):  
Heat Flow ◽  
Thermal Evolution ◽  
The Core ◽  
The Earth ◽  
Minimum Heat

Adiabatic Heat Flow in Mercury with a Fe-8.5wt%Si Core

2021 ◽  
Author(s):  
Meryem Berrada ◽  
Richard Secco ◽  
Wenjun Yong
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Internal Structure ◽  
High Pressures ◽  
Inner Core ◽  
Thermal Evolution ◽  
The Core ◽  
Thermally Driven ◽  
Wire Method ◽  
Core Conditions

<p>Recent theoretical studies have tried to constrain Mercury’s internal structure and composition using thermal evolution models. The presence of a thermally stratified layer of Fe-S at the top of an Fe-Si core has been suggested, which implies a sub-adiabatic heat flow on the core side of the CMB. In this work, the adiabatic heat flow at the top of the core was estimated using the electronic component of thermal conductivity (k<sub>el</sub>), a lower bound for thermal conductivity. Direct measurements of electrical resistivity (ρ) of Fe-8.5wt%Si at core conditions can be related to k<sub>el</sub> using the Wiedemann-Franz law. Measurements were carried out in a 3000 ton multi-anvil press using a 4-wire method. The integrity of the samples at high pressures and temperatures was confirmed with electron-microprobe analysis of quenched samples at various conditions. Unexpected behaviour at low temperatures between 6-8 GPa may indicate an undocumented phase transition. Measurements of ρ at melting seem to remain constant at 127 µΩ·cm from 10-24 GPa, on both the solid and liquid side of the melting boundary. The adiabatic heat flow at the core side of Mercury’s core-mantle boundary is estimated between 21.8-29.5 mWm<sup>-2</sup>, considerably higher than most models of an Fe-S or Fe-Si core yet similar to models of an Fe core. Comparing these results with thermal evolution models suggests that Mercury’s dynamo remained thermally driven up to 0.08-0.22 Gyr, at which point the core became sub-adiabatic and stimulated a change from dominant thermal convection to dominant chemical convection arising from the growth of an inner core. Simply considering the internal structure of Mercury, these results support the capture of Mercury into a 3:2 resonance orbit during the thermally driven era of the dynamo.</p>

scholarly journals Effect of core electrical conductivity on core surface flow models

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Masaki Matsushima
Keyword(s):  
Boundary Layer ◽  
Electrical Conductivity ◽  
Lorentz Force ◽  
Thermal Evolution ◽  
Surface Flow ◽  
Core Flow ◽  
Core Surface ◽  
Flow Models ◽  
The Core ◽  
The Earth

AbstractThe electrical conductivity of the Earth’s core is an important physical parameter that controls the core dynamics and the thermal evolution of the Earth. In this study, the effect of core electrical conductivity on core surface flow models is investigated. Core surface flow is derived from a geomagnetic field model on the presumption that a viscous boundary layer forms at the core–mantle boundary. Inside the boundary layer, where the viscous force plays an important role in force balance, temporal variations of the magnetic field are caused by magnetic diffusion as well as motional induction. Below the boundary layer, where core flow is assumed to be in tangentially geostrophic balance or tangentially magnetostrophic balance, contributions of magnetic diffusion to temporal variation of the magnetic field are neglected. Under the constraint that the core flow is tangentially geostrophic beneath the boundary layer, the core electrical conductivity in the range from $${10}^{5} ~\mathrm{S}~{\mathrm{m}}^{-1}$$ 10 5 S m - 1 to $${10}^{7}~ \mathrm{S}~{\mathrm{m}}^{-1}$$ 10 7 S m - 1 has less significant effect on the core flow. Under the constraint that the core flow is tangentially magnetostrophic beneath the boundary layer, the influence of electrical conductivity on the core flow models can be clearly recognized; the magnitude of the mean toroidal flow does not increase or decrease, but that of the mean poloidal flow increases with an increase in core electrical conductivity. This difference arises from the Lorentz force, which can be stronger than the Coriolis force, for higher electrical conductivity, since the Lorentz force is proportional to the electrical conductivity. In other words, the Elsasser number, which represents the ratio of the Lorentz force to the Coriolis force, has an influence on the difference. The result implies that the ratio of toroidal to poloidal flow magnitudes has been changing in accordance with secular changes of rotation rate of the Earth and of core electrical conductivity due to a decrease in core temperature throughout the thermal evolution of the Earth.

The first 800 million years of Earth's history

1981 ◽  
Vol 301 (1461) ◽  
pp. 401-422 ◽  
Keyword(s):  
Heat Flow ◽  
Upper Mantle ◽  
Calc Alkaline ◽  
Radiogenic Heat ◽  
Crustal Rocks ◽  
The Core ◽  
The Earth ◽  
Equilibrium Data ◽  
Geochemical Transport ◽  
Lunar Basins

The Earth grew initially from hot planetesimals of reduced material, and began to differentiate early into a metal-rich core, a silicate-rich mantle and a volcanic surface. Accretion ended with volatile-rich oxidized material, which did not interact with the core because of a mantle barrier. Quenching of magmas at the surface and foundering of cool material was effective in cooling the Earth by 1600 J per gram of magma. Magmas transported radioactive elements and volatiles to the outer 50 km. The lower mantle became stranded below the critical adiabat for melting. The core may have been fully molten. Radiogenic and non-radiogenic heat sources produced a surface heat flow that decreased from ca . 1.3 x 10 14 W at 4.45 Ga B.P . to the present value of 4 x 10 13 W. In spite of uncertainties in the production and transport of heat, it seems safe to conclude that intense volcanism occurred throughout the pre-Archaean era before survival of crust. From phase-equilibrium data for peridotites and calc-alkaline rocks, it is deduced that a range of ultrabasic to basic magmas was produced from a peridotitic upper mantle, and that calc-alkaline magmas were produced during foundering of crust. An anorthositic crust was not formed. From observations of lunar basins, it is concluded that a minimum of ca . 500-1000 impact basins were formed on Earth in ca . 100—200 Ma before 3.95 Ga B.P. Plausible calculations suggest that ca . 20 times as many basins were formed in the preceding ca . 300 Ma. Impact debris would be cooled by water in wet crustal rocks and oceans. It is assumed that after 4.0 Ga B.P. impacts would have only temporary local effects on the crust, and emphasis is placed on upper-mantle convection as the main driving force for geochemical transport. Sedimentation and metamorphism were important factors during foundering of crust. ‘Oceanic' and ‘continental' regions developed above up-welling and down-welling segments of convection cells, and these regions resembled greenstone belts and high-grade regions of the Archaean era. As heat flow declined, polygonal tectonics was replaced by symmetrical linear tectonics during the Archaean era, and then by asymmetrical linear tectonics during the Proterozoic era.

Ups and Downs

2018 ◽  
Author(s):  
Roy Livermore
Keyword(s):  
Mantle Convection ◽  
Laboratory Experiments ◽  
Inner Core ◽  
Computer Modelling ◽  
Great Depth ◽  
New Horizons ◽  
The Core ◽  
The Earth ◽  
The World ◽  
The 1960S

Despite the dumbing-down of education in recent years, it would be unusual to find a ten-year-old who could not name the major continents on a map of the world. Yet how many adults have the faintest idea of the structures that exist within the Earth? Understandably, knowledge is limited by the fact that the Earth’s interior is less accessible than the surface of Pluto, mapped in 2016 by the NASA New Horizons spacecraft. Indeed, Pluto, 7.5 billion kilometres from Earth, was discovered six years earlier than the similar-sized inner core of our planet. Fortunately, modern seismic techniques enable us to image the mantle right down to the core, while laboratory experiments simulating the pressures and temperatures at great depth, combined with computer modelling of mantle convection, help identify its mineral and chemical composition. The results are providing the most rapid advances in our understanding of how this planet works since the great revolution of the 1960s.

Part 2. The deeper structure of the Atlantic - Geological hypotheses and the earth's crust under the oceans

1954 ◽  
Vol 222 (1150) ◽  
pp. 341-348 ◽  
Keyword(s):  
Heat Flow ◽  
Recent Work ◽  
Sea Water ◽  
Volcanic Rocks ◽  
The Other ◽  
Ocean Floor ◽  
Peridotite Xenoliths ◽  
The Earth ◽  
Southern Rhodesia ◽  
Mohorovičić Discontinuity

Recent work has determined the depth of the Mohorovičić discontinuity at sea and has made it likely that peridotite xenoliths in basaltic volcanic rocks are samples of material from below the discontinuity. It is now possible to produce a hypothetical section showing the transition from a continent to an ocean. This section is consistent with both the seismic and gravity results. The possible reactions of the crust to changes in the total volume of sea water are dis­cussed. It seems possible that the oceans were shallower and the crust thinner in the Archean than they are now. If this were so, some features of the oldest rocks of Canada and Southern Rhodesia could be explained. Three processes are described that might lead to the formation of oceanic ridges; one of these involves tension, one compression and the other quiet tectonic conditions. It is likely that not all ridges are formed in the same way. It is possible that serpentization of olivine by water rising from the interior of the earth plays an important part in producing changes of level in the ocean floor and anomalies in heat flow. Finally, a method of reducing gravity observations at sea is discussed.

scholarly journals Nuclear equation of state and neutron star cooling

2017 ◽  
Vol 26 (04) ◽  
pp. 1750015 ◽  
Author(s):  
Yeunhwan Lim ◽  
Chang Ho Hyun ◽  
Chang-Hwan Lee
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Nuclear Matter ◽  
Thermal Evolution ◽  
Observation Data ◽  
Nuclear Equation Of State ◽  
The Core ◽  
Dense Nuclear Matter ◽  
Nuclear Models

In this paper, we investigate the cooling of neutron stars with relativistic and nonrelativistic models of dense nuclear matter. We focus on the effects of uncertainties originated from the nuclear models, the composition of elements in the envelope region, and the formation of superfluidity in the core and the crust of neutron stars. Discovery of [Formula: see text] neutron stars PSR J1614−2230 and PSR J0343[Formula: see text]0432 has triggered the revival of stiff nuclear equation of state at high densities. In the meantime, observation of a neutron star in Cassiopeia A for more than 10 years has provided us with very accurate data for the thermal evolution of neutron stars. Both mass and temperature of neutron stars depend critically on the equation of state of nuclear matter, so we first search for nuclear models that satisfy the constraints from mass and temperature simultaneously within a reasonable range. With selected models, we explore the effects of element composition in the envelope region, and the existence of superfluidity in the core and the crust of neutron stars. Due to uncertainty in the composition of particles in the envelope region, we obtain a range of cooling curves that can cover substantial region of observation data.

Dead-Ends and New Directions

2021 ◽  
Vol 15 (4) ◽  
pp. 327-347
Author(s):  
Jean Francesco A.L. Gomes
Keyword(s):  
Natural History ◽  
Scientific Theory ◽  
Good Science ◽  
Orthodox Christian ◽  
The Core ◽  
The Earth ◽  
New Directions ◽  
History Of ◽  
Evolutionary Science ◽  
Doctrine Of Creation

Abstract The aim of this article is to investigate how Abraham Kuyper and some late neo-Calvinists have addressed the doctrine of creation in light of the challenges posed by evolutionary scientific theory. I argue that most neo-Calvinists today, particularly scholars from the Vrije Universiteit Amsterdam (VU), continue Kuyper’s legacy by holding the core principles of a creationist worldview. Yet, they have taken a new direction by explaining the natural history of the earth in evolutionary terms. In my analysis, Kuyper’s heirs at the VU today offer judicious parameters to guide Christians in conversation with evolutionary science, precisely because of their high appreciation of good science and awareness of the nonnegotiable elements that make up the orthodox Christian narrative.

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