Density distribution in the Earth

Williamson, Erskine D.; Adams, L. H.

doi:10.1029/sp026p0001

Cited by 25 publications

(27 citation statements)

References 738 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In equation (4), K s is the isentropic bulk modulus, defined by the first equality, and the second equality expresses the choice made here to consider only a linear variation with pressure, the subscript 0 giving values at the center (r = 0). This amounts to using the Adams-Williamson equation (Williamson and Adams, 1923), as is done for example in PREM to relate density to the seismic velocity (Poirier, 2000). This equation of state is simpler than the one used by Labrosse et al (2001) but the results are compatible, at least to the second order that was considered in that former study.…”

Section: Radial Structure Of the Corementioning

confidence: 88%

Thermal evolution of the core with a high thermal conductivity

Labrosse

2015

Physics of the Earth and Planetary Interiors

181

271

View full text Add to dashboard Cite

The rate at which heat is extracted across the core mantle boundary (CMB) is constrained by the requirement of dynamo action in the core. This constraint can be computed explicitly using the entropy balance of the core and depends on the thermal conductivity, whose value has been revised upwardly. A high order model (fourth degree polynomial of the radial position) for the core structure is derived and the implications for the core cooling rate and thermal evolution obtained, using the recent values of the thermal conductivity. For a thermal conductivity increasing with depth as proposed by some of these recent studies, a CMB heat flow equal to the isentropic value (13.25TW at present) leads to a 700 km thick layer at the top of the core where a downward convective heat flow is necessary to maintain an isentropic and well mixed average state. Considering a CMB heat flow larger than the well mixed isentropic value leads to an inner core less than 700 Myr old and the thermal evolution of the core is largely constrained by the conditions for dynamo action without an inner core. Analytical calculations for that period show that a CMB temperature larger than 7000 K must have prevailed 4.5 Gyr ago if the geodynamo has been driven by thermal convection for that whole time. This raises questions regarding the onset of the geodynamo and its continuous operation for the last 3.5 Gyr. Implications regarding the evolution of a basal magma ocean are also considered.

show abstract

Section: Radial Structure Of the Corementioning

confidence: 88%

Thermal evolution of the core with a high thermal conductivity

Labrosse

2015

Physics of the Earth and Planetary Interiors

181

271

View full text Add to dashboard Cite

show abstract

“…In contrast, Williamson and Adams [1923] argued for a varying composition with depth. In their proposed Earth structure the greatest departure from the contemporary view was a gradual change in composition below about 1600 km depth through a mixed silicate and iron region.…”

Section: Nature Of the 410 520 And 660mentioning

confidence: 99%

Topography of the transition zone seismic discontinuities

Helffrich¹

2000

Reviews of Geophysics

256

192

View full text Add to dashboard Cite

Abstract.Phase transformations in mantle mineralogies probably cause the transition zone seismic discontinuities, nominally at 410, 520, and 660 km depth. , 1923]. This paper focuses on the mantle discontinuities in the transition zone, the region between about 400 and 800 km depth. Whereas in seismology's nascency new discontinuity discoveries progressively refined our basic knowledge of Earth structure, in its maturity the discontinuities themselves become investigative tools rather than investigative targets. The goal of this review is to show how changes in discontinuity depth have been and can be used to investigate the mantle's properties. The argument develops along two lines. The first establishes what the major discontinuities at 410, 520, and 660 km depth are. Significantly, the topography on the discontinuities gives strong evidence to discriminate among different ideas about how they arise. The second strand describes the sort of scientific craftsmanship that can be achieved using the spatial variation of discontinuity depths as a tool, a tool that turns out to be surprisingly versatile, under continual refinement, and increasingly common in a research seismologist's tool kit. Detecting DiscontinuitiesSeismic discontinuities are detected by the additional arrivals they cause in the seismic wave field by reflection and refraction of the direct wave at the discontinuity. Reflection typically leads to an earlier arrival than would be expected in a uniform medium. Its timing relative to the direct arrival yields the discontinuity's depth. A refraction usually leads to more than one arrival, where only one would be expected in a uniform medium. In this case, one deduces the discontinuity depth from the distance from the seismic source where the multiple arrivals appear. The Earth's major discontinuities were initially discovered this way, and others continue to be discovered like this [Oldham, 1906;Lehmann, 1936;Song and Helmberger, 1998].There are quite diverse methods for measuring discontinuity depths, probably best described through sketches (Figure 2) (see Shearer [1991] for more exotic ones). One way to characterize the methods is by the position where the seismic wave interacts with the discontinuity: near the source, near the receiver, or elsewhere. Near-source studies provide the best spatial resolution because there is little opportunity for the seismic wave field to spread out before interacting with the discontinuity (its Fresnel zone width is small). Spatial resolution for near-receiver studies is worse since the interaction is at least 410 km from the receiver. Interac-

show abstract

“…Both the Earth's core and the Earth's mantle are compressed by the weight of the mass above (Birch, 1964;Dziewonski and Anderson, 1981;Williamson and Adams, 1923). As shown in Fig.…”

Section: Historical Misunderstanding: Physical Impossibility Of Earthmentioning

confidence: 88%

Inseparability of science history and discovery

Herndon¹

2010

Hist. Geo Space. Sci.

View full text Add to dashboard Cite

Abstract. Science is very much a logical progression through time. Progressing along a logical path of discovery is rather like following a path through the wilderness. Occasionally the path splits, presenting a choice; the correct logical interpretation leads to further progress, the wrong choice leads to confusion. By considering deeply the relevant science history, one might begin to recognize past faltering in the logical progression of observations and ideas and, perhaps then, to discover new, more precise understanding. The following specific examples of science faltering are described from a historical perspective: (1) Composition of the Earth's inner core; (2) Giant planet internal energy production; (3) Physical impossibility of Earth-core convection and Earth-mantle convection, and; (4) Thermonuclear ignition of stars. For each example, a revised logical progression is described, leading, respectively, to: (1) Understanding the endo-Earth's composition; (2) The concept of nuclear georeactor origin of geo-and planetary magnetic fields; (3) The invalidation and replacement of plate tectonics; and, (4) Understanding the basis for the observed distribution of luminous stars in galaxies. These revised logical progressions clearly show the inseparability of science history and discovery. A different and more fundamental approach to making scientific discoveries than the frequently discussed variants of the scientific method is this: An individual ponders and through tedious efforts arranges seemingly unrelated observations into a logical sequence in the mind so that causal relationships become evident and new understanding emerges, showing the path for new observations, for new experiments, for new theoretical considerations, and for new discoveries. Science history is rich in "seemingly unrelated observations" just waiting to be logically and causally related to reveal new discoveries.

show abstract

Density distribution in the Earth

Cited by 25 publications

References 738 publications

Thermal evolution of the core with a high thermal conductivity

Thermal evolution of the core with a high thermal conductivity

Topography of the transition zone seismic discontinuities

Inseparability of science history and discovery

Contact Info

Product

Resources

About