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.

Mineral phases of the Earth´s mantle

2001 ◽  
Vol 216 (5) ◽  
Author(s):  
G. Fiquet
Keyword(s):  
Seismic Waves ◽  
Mineralogical Composition ◽  
X Ray Diffraction ◽  
Temperature Behaviour ◽  
Mineral Physics ◽  
The Earth ◽  
Mineral Phases ◽  
High Pressure High Temperature ◽  
Deep Earth ◽  
Essential Knowledge

AbstractOur knowledge of the structure of the Earth´s interior has been obtained by analysing seismic waves that travel in the Earth, and the reference Earth global models used by geophysicists are essentially seismological. Depth profiles of the seismic waves velocities reveal that the deep Earth is divided in several shells, separated by velocity and density discontinuities. The main discontinuity located at a depth of 2900 km corresponds to the transition between the mantle and the core. The Earth´s mantle can be further divided into the upper mantle and the lower mantle, with a transition zone characterised by two prominent increases in velocities observed at 410- and 660-km depths. This article will be focused on the mineral phases of the Earth´s mantle. The interpretation of seismological models in terms of chemical composition and temperature relies on the knowledge of the nature, structure and elastic properties of the candidate materials. We will describe to what extent recent advances in experimental mineral physics and X-ray diffraction have yielded essential knowledge on the structure and high-pressure high-temperature behaviour of pertinent materials, and major improvements in our understanding of the chemical and mineralogical composition of the Earth´s mantle.

scholarly journals Sir Harold Jeffreys, 2 April 1891 - 18 March 1989

1990 ◽  
Vol 36 ◽  
pp. 301-333 ◽  
Keyword(s):  
Small Group ◽  
20Th Century ◽  
Lower Mantle ◽  
Seismic Waves ◽  
Classical Mechanics ◽  
The Core ◽  
New Methods ◽  
The Earth ◽  
Physical Study ◽  
Primitive Condition

Harold Jeffreys stood out among the small group of pioneers who developed the physical study of the Earth from its primitive condition at the beginning of the 20th century to its state at the launch of the first Sputnik . He, above all, applied classical mechanics to investigate the interior of the Earth. He showed that the core of the Earth is liquid and that there is a substantial difference between the upper and lower mantle, as we now call them. His massive analyses of travel times of seismic waves (with K.E. Bullen, F.R.S.) are still standards of reference and are currently being brought up to date. Jeffreys retired from his Chair at Cambridge (but certainly not from active study) just after the first Sputnik had been launched, and as powerful new methods in seismology and marine geophysics were coming into use. Geophysics has since expanded out of all recognition so that it is easy to lose sight of Jeffreys’s earlier contributions. There have been considerable changes in the concepts and methods of geophysics from some that he established, yet the major spherically symmetrical elements of the structure of the Earth that he did so much to elucidate, are the basis for all subsequent elaboration, and generations of students learnt their geophysics from his book The Earth .

scholarly journals Observations on seismic waves reflected at the core boundary of the earth*

1950 ◽  
Vol 40 (2) ◽  
pp. 95-109
Author(s):  
Samuel T. Martner
Keyword(s):  
Observational Data ◽  
Seismic Waves ◽  
Outer Boundary ◽  
Body Waves ◽  
Longitudinal Waves ◽  
The Core ◽  
The Earth ◽  
Core Boundary ◽  
Direct Body

Abstract Waves reflected from the outer boundary of the core of the earth often record trace amplitudes that appear excessive. A comparison of the observed displacements of these phases and the direct body waves is presented. Observational data seem to confirm the idea that the displacement ratios of the longitudinal waves reflected at the core to the longitudinal direct waves is larger than the presently recognized theory indicates. A discussion is included of some possible causes for this difference, but reasonable changes in accepted assumptions fail to explain the entire discrepancy.

scholarly journals Attenuation of seismic waves in the earth's mantle

1958 ◽  
Vol 48 (3) ◽  
pp. 269-282 ◽  
Author(s):  
B. Gutenberg
Keyword(s):  
Absorption Coefficient ◽  
Elastic Waves ◽  
Laboratory Experiments ◽  
Seismic Waves ◽  
Body Waves ◽  
The Core ◽  
Earth’S Mantle ◽  
The Earth ◽  
Theoretical Considerations

Abstract Contrasting with conclusions from laboratory experiments that the absorption coefficient k for amplitudes of elastic waves is proportional to 1/T, or, from theoretical considerations, that it should be proportional to 1/T or to 1/T2, observations of body waves through the mantle of the earth show little if any decrease in absorption with increasing period T. In teleseismic records S rarely shows periods of less than 4 seconds, while in P periods of 1 second are observed to the greatest distances. The value k = 0.06 per 1,000 km., found previously for P, P′P′ and P′P′P′ through the mantle and the core, is confirmed for P and PP and is found also for S in the mantle.

The GRACEFUL project : probing the Earth’s deep interior with satellite observations of the gravity field, magnetic field and earth’s rotation

2020 ◽  
Author(s):  
Julia Pfeffer ◽  
Anny Cazenave ◽  
Mioara Mandea ◽  
Véronique Dehant ◽  
Anne Barnoud
Keyword(s):  
Magnetic Field ◽  
Gravity Field ◽  
Liquid Core ◽  
Temporal Variations ◽  
Champ Satellite ◽  
The Core ◽  
Temporal Correlations ◽  
The Earth ◽  
Deep Earth ◽  
Order Of Magnitude

<p><span id="divtagdefaultwrapper" dir="ltr"><span lang="en-US">Convective motions in the Earth’s liquid core are known to  generate temporal variations of the magnetic field and of the length of day. Mass redistribution associated with these motions and exchange of matter with the lower mantle at the core mantle boundary (CMB) may eventually also contribute to the temporal variations of the gravity field, possibly detectable in the data of the GRACE and GRACE Follow On missions. In a pioneering work, Mandea et al., 2012 detected compelling spatio-temporal correlations at interannual time scale between the gravity and magnetic fields measured respectively by the GRACE and CHAMP satellite missions. These correlations were later interpreted by these authors as the results of physico-chemical interactions between the core and the mantle at the CMB. While such mechanisms are plausible, their mere existence, order of magnitude and  time scales remain an open question. Here we present the </span><span lang="en-US"> GRACEFUL project, recently selected by the  "Synergy" programme of the </span><span lang="en-US">European Research Council</span><span lang="en-US">, which objective is to  explore in more detail the previously reported observations described above, in particular the interannual co-variations of the magnetic and gravity fields, as well as their link with deep Earth processes.  This presentation is focussed on the  gravity field component, in particular on the search for the deep Earth signal that we hope to be able to detect i</span><span lang="en-US">n the  GRACE/GRACE FO data,  </span><span lang="en-US">after removing all other contributions due to water mass redistributions  occuring in the surface fluid evelopes, as well as  unrelated solid Earth signals associated with the Glacial Isostatic Adjustment and large earthquakes.</span></span></p>

Geophysics: A Very Short Introduction

2018 ◽  
Author(s):  
William Lowrie
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Plate Tectonics ◽  
Seismic Waves ◽  
Outer Space ◽  
The Sun ◽  
Short Introduction ◽  
The Earth ◽  
Gravity And Magnetic ◽  
Harmful Radiation

Geophysics is the physics of the Earth. It encompasses areas such as seismology, plate tectonics, gravity, and the Earth’s magnetic field, all of which give clues to both the structure and the working of the Earth. Geophysics: A Very Short Introduction describes the internal and external processes that affect the planet, as well as the techniques used by geophysicists to investigate them. It explains how analysis of the seismic waves produced in earthquakes reveals the Earth’s internal structure, and tells how heat is transported through its interior. Chapters describe how satellite missions measure the gravity and magnetic fields, and explain how its magnetic field shields the Earth against harmful radiation from the Sun and outer space.

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.

Seismic Waves in the Core of the Earth

Nature ◽  
1938 ◽  
Vol 141 (3565) ◽  
pp. 371-371 ◽  
Author(s):  
B. GUTENBERG ◽  
C. F. RICHTER
Keyword(s):  
Seismic Waves ◽  
The Core ◽  
The Earth

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.

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