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.

scholarly journals Heat flow from the Earth interior as indicator of deep processes

Georesursy ◽  
2018 ◽  
Vol 20 (4) ◽  
pp. 366-376 ◽  
Author(s):  
B. Polyak ◽  
M. Khutorskoy
Keyword(s):  
Heat Flow ◽  
Hydrothermal Activity ◽  
Conductive Heat ◽  
Radiogenic Heat ◽  
The Earth ◽  
Open Discharge ◽  
Conductive Heat Flow ◽  
Different Depths ◽  
Tectonic Movements ◽  
Energy Aspects

The energy aspects of the problem of intraterrestrial heat transfer in various forms are discussed. Endogenous causes of conductive heat flow dispersion − radiogenic heat generation, tectonic movements and magmatism (volcanism), including its latent and open discharge in the form of volcanic and hydrothermal activity are considered. The geological ordering of the heat flow in the continental crust is related to convective discharge of the heat and mass flux from the mantle, marked by the isotopic composition of helium in freely circulating underground fluids. The combined transport of heat and helium, as well as the correlation of He isotopic compositions in volcanic and hydrothermal gases and Sr compositions in young lavas, testify to the silicate nature of the heat and mass flow emanating from the mantle reservoirs of different depths.

Thermal constraints on the distribution of long-lived radioactive elements in the Earth

1979 ◽  
Vol 291 (1381) ◽  
pp. 269-275 ◽  
Keyword(s):  
Heat Generation ◽  
Heat Production ◽  
Upper Mantle ◽  
High Heat ◽  
Geochemical Data ◽  
Radioactive Elements ◽  
The Core ◽  
Thermal Constraints ◽  
The Earth ◽  
Qualitative Models

Geochemical data show that radioactive heat production in the crust plus upper mantle (which is defined seismically to terminate at a depth of 415 km) cannot account for the heat escaping from the Earth. Deeper sources must be invoked, and a number of qualitative models of the variation of radioactive heat generation with depth are suggested. Preferred models involve a narrow zone of high heat production about halfway between the crust and the core.

5. Rocks in the deep

2016 ◽  
pp. 66-79
Author(s):  
Jan Zalasiewicz
Keyword(s):  
Magnetic Fields ◽  
Upper Mantle ◽  
Lower Crust ◽  
Seismic Waves ◽  
Direct Experience ◽  
Rock Fragments ◽  
The Core ◽  
The Earth ◽  
Deep Earth ◽  
Volcanic Processes

It is over 6,000 km to the centre of the Earth, but our direct experience of its rocks goes to little more than 3 km below the surface in the deepest mines on Earth. ‘Rocks in the deep’ shows that we can find out more by assessing rock fragments brought from deeper levels by tectonic or volcanic processes; by analysing patterns of change in the gravitational and magnetic fields; by detecting seismic waves that have travelled through the Earth; or by recreating conditions of the deep Earth in the laboratory. It describes what is known about the lower crust, the upper mantle, the deep mantle, and the core.

Universal dispersion tables

1969 ◽  
Vol 59 (4) ◽  
pp. 1667-1693
Author(s):  
Don L. Anderson ◽  
Robert L. Kovach
Keyword(s):  
Upper Mantle ◽  
Free Oscillation ◽  
Velocity Structure ◽  
Shear Velocity ◽  
Average Density ◽  
Earth Model ◽  
The Core ◽  
The Earth ◽  
Small Change ◽  
Dominant Parameter

Abstract The effect of a small change in any parameter of a realistic Earth model on the periods of free oscillation is computed for both spheroidal and torsional modes. The normalized partial derivatives, or variational parameters, are given as a function of order number and depth in the Earth. For a given mode it can immediately be seen which parameters and which regions of the Earth are controlling the period of free oscillation. Except for oSo and its overtones the low-order free oscillations are relatively insensitive to properties of the core. The shear velocity of the mantle is the dominant parameter controlling the periods of free oscillation and density can be determined from free oscillation data only if the shear velocity is known very accurately. Once the velocity structure is well known free oscillation data can be used to modify the average density of the upper mantle. The mass and moment of inertia are then the main constraints on how the mass must be redistributed in the lower mantle and core.

Composition of Earth

2021 ◽  
Author(s):  
H. Palme
Keyword(s):  
Upper Mantle ◽  
Core Formation ◽  
Formation Model ◽  
Major Element Composition ◽  
The Core ◽  
The Earth ◽  
The 1960S ◽  
Isotope Analyses ◽  
Uniform Composition

Early models of the composition of the Earth relied heavily on meteorites. In all these models Earth had different layers, each layer corresponded to a different type of meteorite or meteorite component. Later, more realistic models based on analyses of samples from Earth began with Ringwood’s pyrolite composition in the 1960s. Further improvement came with the analyses of rare MgO rich peridotites from a variety of occurrences all over the Earth, as xenoliths enclosed in melts from the upper mantle or as ultramafic massifs, tectonically emplaced on the Earth’s surface. Chemical systematics of these rocks allow the determination of the major element composition of the primitive upper mantle (PUM), the upper mantle after core formation and before extraction of basalts ultimately leading to the formation of the crust. Trace element analyses of upper mantle rocks confirmed their primitive nature. Geochemical and geophysical evidence argue for a bulk Earth mantle of uniform composition, identical to the PUM, also designated as “bulk silicate Earth” (BSE). The formation of a metal core was accompanied by the removal of siderophile and chalcophile elements into the core. Detailed modeling suggests that core formation was an ongoing process parallel to the accretion of Earth. The composition of the core is model dependent and thus uncertain and makes reliable estimates for siderophile and chalcophile element concentrations of bulk Earth difficult. Improved stable isotope analyses show isotopic similarities with noncarbonaceous chondrites (NCC), while the chemical composition of the mantle of the Earth indicates similarities with carbonaceous chondrites (CC). In detail, however, it can be shown that no single known meteorite group, nor any mixture of meteorite groups can match the chemical and isotopic composition of Earth. This conclusion is extremely important for any formation model of the Earth.

Geochemical Constraints on the Early Thermal History of the Earth

1989 ◽  
Vol 44 (10) ◽  
pp. 883-890 ◽  
Author(s):  
Michael J. Drake
Keyword(s):  
Upper Mantle ◽  
Partition Coefficients ◽  
Current Theory ◽  
Gravitational Potential Energy ◽  
The Moon ◽  
The Core ◽  
The Earth ◽  
History Of ◽  
Geochemical Constraints ◽  
Origin Of The Moon

Abstract Theories of the formation of the Earth strongly suggest that the Earth should have been substantially molten during and immediately after accretion. Estimates of the composition of the upper mantle indicate that many elements are present in chondritic ratios. Experimental measurements of element partition coefficients show that segregation of perovskite, majorite garnet, or olivine would fractionate the ratios of these elements away from chondritic values. The implication of these geochemical observations is that the Earth did not undergo extensive fractionation during and immediately following accretion. One possibility is that the Earth did not become substantially molten. Alternatively, if the Earth was indeed substantially molten, then it is possible that minerals were entrained in magma and were unable to segregate. In the former case, the accretional process must have delivered gravitational potential energy more slowly than current theory predicts, and an origin of the Moon in a giant impact would be unlikely. In the latter case, the high Mg/Si ratio in the upper mantle of the Earth relative to most classes of chondrites would be intrinsic to the silicate portion of the Earth. Unless significant amounts of Si exist in the core, the high Mg/Si ratio is a bulk planetary property, implying that the accretional process did not mix material between 1 AU and 2-4 AU.

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