On the origin of mountains

1963 ◽  
Vol 275 (1360) ◽  
pp. 1-22 ◽  
Keyword(s):  
Liquid Core ◽  
Linear Functions ◽  
Core Material ◽  
Earth Model ◽  
Mathematical Form ◽  
Initial Surface ◽  
Mantle Material ◽  
Spherical Form ◽  
The Earth ◽  
Central Regions

The hypothesis is adopted that the Earth began as an entirely solid body and gradually became melted in its central regions. The incompressibilities of both the liquid and solid regions are linear functions of the pressure, and this enables an integral pressure-density relation to be found and also the effective uncom pressed densities of the different regions. The equations for hydrostatic equilibrium can be reduced to a standard mathematical form, while Earth-models can be related to their solution by homologies with factors depending on the mass and physical constants of the material. An Earth of purely mantle-material and solid throughout would have radius 1.043 times the present radius, while allowance for lower uncompressed density of the outer layers increases this to 1.056 R E . This implies an initial surface area nearly 60 million square kilometres in excess of the present area. The liquid core-material is more compressible than the solid mantle-material at the pressures prevailing deep within the Earth, and it results that as the size of the core gradually increases, the composite Earth-model decreases in overall radius. The extreme lower limit of size corresponding to an entirely molten Earth would be 0.846 R E . The slow contraction of the entire Earth will gradually build up shearing stresses at and near the surface that the material there will eventually be unable to withstand, and periods of surface folding and thrusting will occur intermittently to relieve these stresses. Down to a depth of a few kilometres, less potential energy would be involved in piling up material against gravity than would be required in compressing it horizontally to maintain perfectly spherical form. The Earth would therefore prefer to buckle at the surface thereby remaining as uncompressed as possible at its outer parts. The theory suggests that Venus will have developed in much the same way as the Earth. On the other hand, because of the much lower pressures within the Moon, Mercury, and Mars, these objects are still solid throughout, and if melting ever occurs it would probably result in their expansion, not in contraction. Accordingly, thrusted and folded mountains would not be expected to be found on these bodies.

Constraints on core composition from shock-waves data

1982 ◽  
Vol 306 (1492) ◽  
pp. 37-47 ◽  
Keyword(s):  
Equations Of State ◽  
Liquid Core ◽  
Light Element ◽  
Outer Core ◽  
Atomic Ratio ◽  
Core Material ◽  
Solar Photosphere ◽  
The Core ◽  
The Earth ◽  
Core Composition

Seismic data demonstrate that the density of the liquid core is some 8-10 % less than pure iron. Equations of state of Fe-Si, C, FeS 2 , FeS, KFeS 2 and FeO, over the pressure interval 133-364 GPa and a range of possible core temperatures (3500- 5000 K), can be used to place constraints on the cosmochemically plausible light element constituents of the core (Si, C, S, K and O ). The seismically derived density profile allows from 14 to 20 % Si (by mass) in the outer core. The inclusion of Si, or possibly G (up to 11 %), in the core is possible if the Earth accreted inhomogeneously within a region of the solar nebulae in which a C :0 (atomic) ratio of about 1 existed, compared with a G : O ratio of 0.6 for the present solar photosphere. In contrast, homogeneous accretion permits Si, but not C, to enter the core by means of reduction of silicates to metallic Fe-Si core material during the late stages of the accumulation of the Earth. The data from the equation of state for the iron sulphides allow up to 9-13 % S in the core. This composition would provide the entire Earth with a S:Si ratio in the range 0.14-0.3, comparable with meteoritic and cosmic abundances. Shock-wave data for KFeS 2 give little evidence for an electronic phase change from 4s to 3d orbitals, which has been suggested to occur in K, and allow the Earth to store a cosmic abundance of K in the metallic core.

scholarly journals Rotational Velocity of an Earth Model with a Liquid Core

1979 ◽  
Vol 82 ◽  
pp. 313-314
Author(s):  
S. Takagi
Keyword(s):  
Rotational Motion ◽  
Velocity Vector ◽  
Inner Core ◽  
Rotational Velocity ◽  
Equations Of Motion ◽  
Liquid Core ◽  
Outer Core ◽  
Earth Model ◽  
The Earth ◽  
Rotation Of The Earth

There have been many papers discussing the rotation of the Earth (Jeffreys and Vicente, 1957; Molodenskij, 1961; Rochester, 1973; Smith, 1974; Shen and Mansinha, 1976). This report summarizes the application of the perturbation method of celestial mechanics to calculate the rotation of the Earth (Takagi, 1978). In this solution the Earth is assumed to consist of three components: a mantle, liquid outer core, and a solid inner core, each having a separate rotational velocity vector. Hamiltonian equations of motion were constructed to solve the rotational motion of the Earth.

On the phase-change hypothesis of the structure of the Earth

1965 ◽  
Vol 287 (1411) ◽  
pp. 471-493 ◽  
Keyword(s):  
Phase Change ◽  
Average Rate ◽  
Liquid Core ◽  
Rotation Period ◽  
Crystal Form ◽  
Outer Radius ◽  
Gravitational Energy ◽  
The Earth ◽  
Slow Expansion ◽  
Central Regions

The hypothesis that the liquid core of the Earth represents a phase-change at high pressure (and suitable temperature) of the mantle material is further investigated. A more accurate series of two-zone models have been computed, and also a new series of three-zone models. The change of overall radius as between an original all-solid Earth and the present size is shown to be at least 370 km. In the outer regions, greater pressure may be needed with rising temperature to effect the transition to denser crystal form (associated with the 20°-discontinuity), and from this cause acting alone slight expansion of the Earth would result but to an extent less than one-tenth the overall contraction. Epochs of rapid contraction (mountain-building eras) could thus be separated by longer intervals of very slow expansion. The initial liquefaction of the central regions brings about pressure increase at the boundary of the core that renders the Earth unstable in that about 6 per cent of the entire mass liquefies extremely rapidly to cause a sudden collapse of the planet as a whole. The accompanying decrease of outer radius is about 70 km. Thereafter the planet remains thoroughly stable and contracts only slowly. The total contraction to date would have reduced the moment of inertia by a factor about 4/5, and the corresponding reduction in rotation period (through conservation of angular momentum) would be an effect comparable with tidal friction. The contraction also leads to release of gravitational energy at an average rate comparable with that from radioactive sources. An important consequence of the phase-change hypothesis is that the melting-point gradient changes sign after sufficient depth, thereby permitting melting of the central regions to occur at moderate temperatures explicable by a reasonable content of radioactive elements.

Development of deep-seated magma sources throughout the Earth’s history: Evidence from evolution of the large igneous provinces (LIPs)

2020 ◽  
Author(s):  
Evgenii Sharkov ◽  
Maria Bogina ◽  
Alexei Chistyakov
Keyword(s):  
Liquid Core ◽  
Core Material ◽  
Mantle Plumes ◽  
Early Precambrian ◽  
Large Igneous Provinces ◽  
Early Stages ◽  
The Earth ◽  
Igneous Provinces ◽  
Essential Change ◽  
Magma Sources

<p>Most researchers believe that large igneous provinces (LIPs) are formed by adiabatic melting of heads of ascending mantle plumes. Because the LIPs have existed throughout the geological history of the Earth (Ernst, 2014), their rocks can be used to probe the plume composition and to decipher the evolution of deep-seated processes in the Earth’s interior.</p><p>The early stages of the LIPs evolution are discussed by the example of the eastern Fennoscandian Shield, where three major LIP types successively changed each other during the early Precambrian: (1) Archean LIP composed mainly of komatiite-basaltic series, (2) Early Paleoproterozoic LIP made up mainly of siliceous high-Mg series, and (3) Mid-Paleoproterozoic LIP composed of picrites and basalts similar to the Phanerozoic LIPs (Sharkov, Bogina, 2009). The two former types of LIPs derived from high-Mg depleted ultramafic material practically were extinct after the Mid-Paleoproterozoic, whereas the third type is survived till now without essential change. The magmas of this LIP sharply differed in composition. Like in Phanerozoic LIPs, they were close to E-MORB and OIB and characterized by the elevated and high contents of Fe, Ti, P, alkalis, LREE, and other incompatible elements (Zr, Ba, Nb, Ta, etc.), which are typical of geochemically enriched plume sources.</p><p>According to modern paradigm (Maruyama, 1994; Dobretsov, 2010; French, Romanowiсz, 2015, etc.), formation of such LIPs is related to the ascending thermochemical mantle plumes, generated at the mantle-liquid core boundary due to the percolation of the core’s fluids into overlying mantle. Thus, these plumes contain two types of material, which provide two-stage melting of the plume’s heads: adiabatic and fluid-assisted incongruent melting of peridotites of upper cooled margins (Sharkov et al., 2017).</p><p>These data indicate that the modern setting in the Earth’s interior has existed since the Mid Paleoproterozoic (~2.3 Ga) and was sharply different at the early stages of the Earth’s evolution. What was happened in the Mid Paleoproterozoic? Why thermochemical plumes appeared only at the middle stages of the Earth’s evolution? It is not clear yet. We suggest that this could be caused by the involvement of primordial core material in the terrestrial tectonomagmatic processes.  This core survived from the Earth’s heterogeneous accretion owing to its gradual centripetal warming accompanied by cooling of outer shells (Sharkov, Bogatikov, 2010).</p><p>References</p><p>Dobretsov, N.L. (2008). Geological implications of the thermochemical plume model. Russian Geology and Geophysics, <strong>49</strong> (7), 441-454.</p><p>Ernst, R.E. (2014). Large Igneous Provinces. Cambridge Univ. Press, Cambridge, 653 p.</p><p>French, S.W., Romanowicz, B. (2015). Broad plumes rooted at the base of the Earth’s mantle beneath major hotspots. Nature, <strong>525</strong>, 95-99.</p><p>Maruyama, S. (1994). Plume tectonics. Journal of Geological Society of Japan, 100, 24-49.</p><p>Sharkov, E.V., Bogina, M.M. (2009). Mafic-ultramafic magmatism of the Early Precambrian (from the Archean to Paleoproterozoic)<strong>.</strong> Stratigraphy and Geological Correlation, 17, 117-136.</p><p>Sharkov, E.V., Bogatikov, O.A. (2010). Tectonomagmatic evolution of the Earth and Moon // Geotectonics 44(2), 83-101.</p><p>Sharkov, E., Bogina, M., Chistyakov, A. (2017). Magmatic systems of large continental igneous provinces. Geoscience Frontiers 8(4), 621-640</p><p> </p>

Correlation between large-scale motions in the liquid core of the Earth and geomagnetic jerks, earthquakes, and variations in the Earth’s length of day

2016 ◽  
Vol 467 (1) ◽  
pp. 280-283 ◽  
Author(s):  
M. B. Gokhberg ◽  
E. V. Olshanskaya ◽  
O. G. Chkhetiani ◽  
S. L. Shalimov ◽  
O. M. Barsukov
Keyword(s):  
Large Scale ◽  
Liquid Core ◽  
Length Of Day ◽  
The Earth ◽  
Geomagnetic Jerks

2.1.3.2 The earth model

2005 ◽  
pp. 85-96
Author(s):  
A. M. Dziewonski ◽  
D. L. Anderson
Keyword(s):  
Earth Model ◽  
The Earth

scholarly journals Nutation in Space and Diurnal Nutation in the Case of an Elastic Earth

1979 ◽  
Vol 82 ◽  
pp. 169-174 ◽  
Author(s):  
Nicole Capitaine
Keyword(s):  
Rotation Axis ◽  
Liquid Core ◽  
Elastic Earth ◽  
The Earth ◽  
Earth’S Interior ◽  
Earth's Interior

In order to improve the representation of nutation, the effect of elasticity of the Earth on the nutation in space and diurnal nutation of the terrestrial rotation axis is considered and its amplitude is evaluated for the principal terms. The choice between several methods taking this effect into account is discussed. A comparison with the effect induced on nutation by the existence of a liquid core in the Earth's interior shows that the consideration of elasticity alone cannot give any amelioration in the representation of nutation.

scholarly journals Rigid-Earth Nutation Models

2000 ◽  
Vol 180 ◽  
pp. 190-195
Author(s):  
J. Souchay
Keyword(s):  
Transfer Function ◽  
Rigid Body ◽  
Earth Model ◽  
High Quality ◽  
Frequency Dependent ◽  
Relative Improvement ◽  
The Earth ◽  
Rigid Earth

AbstractDespite the fact that the main causes of the differences between the observed Earth nutation and that derived from analytical calculations come from geophysical effects associated with nonrigidity (core flattening, core-mantle interactions, oceans, etc…), efforts have been made recently to compute the nutation of the Earth when it is considered to be a rigid body, giving birth to several “rigid Earth nutation models.” The reason for these efforts is that any coefficient of nutation for a realistic Earth (including effects due to nonrigidity) is calculated starting from a coefficient for a rigid-Earth model, using a frequency-dependent transfer function. Therefore it is important to achieve high quality in the determination of rigid-Earth nutation coefficients, in order to isolate the nonrigid effects still not well-modeled.After reviewing various rigid-Earth nutation models which have been established recently and their relative improvement with respect to older ones, we discuss their specifics and their degree of agreement.

Validity of Resolving the 785 km Discontinuity in the Lower Mantle with P′P′ Precursors?

2020 ◽  
Vol 91 (6) ◽  
pp. 3278-3285
Author(s):  
Baolong Zhang ◽  
Xiangfang Zeng ◽  
Jun Xie ◽  
Vernon F. Cormier
Keyword(s):  
Lower Mantle ◽  
Forward Modeling ◽  
Earth Model ◽  
Frequency Content ◽  
Waveform Data ◽  
Mantle Discontinuities ◽  
The Earth ◽  
Earth Models ◽  
Beamforming Technique ◽  
Ray Paths

Abstract P ′ P ′ precursors have been used to detect discontinuities in the lower mantle of the Earth, but some seismic phases propagating along asymmetric ray paths or scattered waves could be misinterpreted as reflections from mantle discontinuities. By forward modeling in standard 1D Earth models, we demonstrate that the frequency content, slowness, and decay with distance of precursors about 180 s before P′P′ arrival are consistent with those of the PKPPdiff phase (or PdiffPKP) at epicentral distances around 78° rather than a reflection from a lower mantle interface. Furthermore, a beamforming technique applied to waveform data recorded at the USArray demonstrates that PKPPdiff can be commonly observed from numerous earthquakes. Hence, a reference 1D Earth model without lower mantle discontinuities can explain many of the observed P′P′ precursors signals if they are interpreted as PKPPdiff, instead of P′785P′. However, this study does not exclude the possibility of 785 km interface beneath the Africa. If this interface indeed exists, P′P′ precursors at distances around 78° would better not be used for its detection to avoid interference from PKPPdiff. Indeed, it could be detected with P′P′ precursors at epicentral distances less than 76° or with other seismic phases such as backscattered PKP·PKP waves.

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