Convection Hypothesis Research Articles

Stellar Aberration from the Standpoint of the Radiation Convection Hypothesis

Stellar Aberration from the Standpoint of the Radiation Convection Hypothesis

Mantle convection and core-mantle boundary topography: explanations and implications

Recent seismic inferences of the topography on the core-mantle boundary (CMB) constitute a new and potentially important constraint on the dynamics of the thermal convective circulation in the Earth's mantle. We employ viscous flow models for the mantle to predict the flow-induced deflections of the CMB that are expected on the basis of seismic tomographic inferences of internal mantle density heterogeneity. The good agreement between our theoretical predictions and the seismically inferred CMB deflections of Morelli and Dziewonski (1987) suggests that the latter may indeed be good approximations to the dynamically induced CMB topography. The amplitude of the seismically inferred CMB topography may be construed to provide a direct constraint on the temperature derivative of seismic P-wave velocity in the lower mantle and we determine a value for this parameter, in the course of fitting the data, that differs significantly from the value determined by laboratory measurements as appropriate for upper-mantle phases. The seismically observed topography on the CMB is also shown to provide evidence favouring the whole-mantle convection hypothesis and in this connection we argue that deep penetration of subducted lithospheric slabs into the lower mantle is likely to be responsible for controlling many of the features of this topography.

Circular convection during subsurface injection of liquid waste, St. Petersburg, Florida

Injection of liquid waste into a highly transmissive, saltwater‐bearing, fractured dolomite underlying the city of St. Petersburg, Florida, provided an opportunity to study density‐dependent flow associated with two miscible and density‐different liquids. The injection zone was 98 m thick with a radial hydraulic conductivity of 762 m/d and a vertical hydraulic conductivity of 152 m/d. Mean chloride concentrations of the injectant during two tests of 91 and 366 days duration were 180 and 170 mg/L, respectively, whereas chloride concentration of native salt water ranged from 19,000 to 20,000 mg/L. During the 366‐day test, chloride concentration in water from a well open to the upper part of the injection zone 223 m from the injection well approximately stabilized at about 4000 mg/L. Relatively constant chloride concentrations in water from this observation well at a level significantly greater than the injectant concentration suggested the hypothesis that circular convection with saltwater flow added chloride ions to the injection zone flow sampled at the observation well. In order to assess the acceptability of the circular convection hypothesis, information was required about the velocity field during injection. Mass transport model simulations were used to provide this information, after determining that the fractured injection zone could be treated as an equivalent porous medium with a single porosity. The mass transport model was calibrated using the 91‐day test data from two observation wells 223 m from the injection well. The model was then run without parameter changes to simulate the 366‐day test. Mass fractions of injectant computed for four observation wells during the 366‐day test compared favorably with observed mass fractions. Observed mass fractions were calculated as a function of chloride concentration and density. Comparisons between model‐computed mass fraction and velocity fields in a radial section showed circular convection, with salt water flowing toward the injection well in the lower part of the injection zone. The salt water then mixed with the injectant, and the mixture flowed away from the injection well in the upper part of the injection zone. On the basis of the model results and the assumed reasonableness of treating the injection zone as an equivalent porous medium with a single porosity, the hypothesis of circular convection with saltwater flow during subsurface injection of liquid waste into a highly transmissive saltwater‐bearing fractured dolomite was judged acceptable.

Predictions of magnetic fields for Uranus and Neptune

The magnetic moments of Uranus and Neptune have been predicted using different scaling laws of planetary magnetism. The predictions for Uranus cover a broad band of values from very weak magnetic fields (tidal relations) to moderate fields (thermal convection hypothesis). Therefore, the direct measurements of this field by Voyager 2 (January 1986) will be very important for testing the individual hapotheses.

The Rheology of the Planetary Interior

The mantle of the earth is rheologically similar to an amorphous polymer. The short‐time‐scale behavior in shear is anelastic and rather well described by a constant Q absorption band. The long‐time‐scale behavior is essentially Newtonian viscous and this mode of deformation dominates the material behavior for times in excess of a Maxwell time which is on the order of 200 years. Most geophysical observations seem to be adequately reconciled by a simple linear viscoelastic rheology which is a generalization of the classical Burger's body and which is uniformly valid in time. This model is particularly useful because there exists a simple analytic expression for the shear modulus in the Laplace transform domain so that correspondence principle methods may be easily applied to solve dynamical problems. This article provides a simple derivation of this expression for the shear modulus and demonstrates the manner in which the unknown rheological parameters may be determined by fitting appropriate geophysical observations. Particular attention is devoted to discussion of the long‐time‐scale viscous response which is a crucial ingredient in the thermal convection hypothesis of continental drift.

The European vestibular experiments in spacelab-1

A series of experiments /1/ were performed in the Spacelab-1 mission on November/December, 1983, pre-, in-, and postflight. These experiments covered various aspects of the functions of the vestibular system, the inflight tests comprising threshold measurements for linear movements in three orthogonal axes, optokinetic stimulation, vestibulo-ocular reflexes under linear and angular accelerations, caloric stimulation with and without linear accelerations; pre- and postflight tests repeated the inflight protocol with the addition of subjective vertical and eye counter-rotation measurements using a tilt table. One of the most surprising and significant results was the caloric test: strong caloric nystagmus on the two subjects tested was recorded inflight; this was contrary to what was expected from Barany's convection hypothesis for caloric nystagmus.

Wegener's theory: The role of geophysics in its eclipse and triumph

Wegener's hypothesis of continental drift was based on a synthesis of world geological observations. Although there was much debate about the correctness of the geological interpretations, the chief objection to the theory came from the absence of a viable geophysical mechanism and in particular from the argument in favour of the mantle having finite strength. By about 1950 the hypothesis was widely rejected by geoscientists but soon after the development of palaeomagnetism provided what was needed to test it: a quantitative method of determining the position of the continents in the geological past. Comparisons of palaeomagnetic polar wandering curves from the different continents provided strong support for the essential ideas which Wegener had put forward. By the early 1960s the hypothesis of convection in the Earth's mantle made possible by solid state creep removed the basic geophysical objections to Wegener's theory. Sea floor spreading neatly complemented continental drift, and integrated into the concept of plate tectonics, has provided a framework in which much other geological and geophysical data fit.

The geoid and single-cell mantle convection

The geoid shows an antisymmetric departure from the spheroid of best fit. A single zero-elevation contour divides its surface into nearly equal strips in one of which the elevation is everywhere positive and in the other everywhere negative. These two areas are interleaved roughly like the strips covering a tennis ball. This pattern may indicate global single-cell convection in the mantle. It is argued that on this convection hypothesis, the upcurrents underlie the low-geoid strip, although the opposite view could be supported. No simple relation is to be expected between the proposed whole-mantle convection and plate motions, because other constraints act on plates and because the asthenosphere will partially decouple the whole-mantle motions from the lithosphere. However, the proposed whole-mantle convective system is consistent with rapid northwestward motion of the Pacific plate, with fast spreading of the East Pacific Rise and with slow spreading of the North Atlantic Ridge. Seismological velocity anomalies in the mantle, while highly relevant to whole-mantle convection, do not at present decide for or against the hypothesis here advanced.

Subterrestrial fluid convection: A hypothesis for long-distance migration of radon within the earth

Scattered observations suggest that radon can migrate through the earth for distances of ≳100 m, a process of great potential aid in both earthquake prediction and uranium exploration. It is noted that existing theories predict that fluid convection in the earth, driven by the local geothermal gradient, can occur in areas of relatively high permeability. The velocity of fluid flow may be sufficient to transport radon over large distances before it decays. The convection hypothesis also provides a possible explanation of seasonal effects that have been observed in local and general radon emanation into the atmosphere.

Martian surface harmonics and continental drift

Recent radar and spectroscopic determinations of topographic heights on Mars reveal that the planet possesses a distribution of surface harmonics similar to that of the Earth. This similarity is manifested in the dominance of the first five harmonics with a rapid decline of higher order terms. An independent study of the Martian grid pattern, composed of lineaments known as the “Martian canals”, indicates the possible presence of convection currents within the Martian mantle. The distribution of areas of rising and descending currents provides a rough estimate of the stress fields in the Martian crust which can explain the position of the sub-equatorial dark maria, a zone now known to be partly composed of continental-type blocks, in terms of a southerly continental drift. These stress regions also suggest that the northern hemisphere feature Mare Acidalium could have formed in a manner similar to the convection hypothesis of the origin of terrestrial mid-oceanic ridges, that the south pole may be a mountainous area, and in general that the Martian linear features are related to tectonic zones of weakness. Other observed features also find a natural explanation in their origin in terms of the harmonics of an internal convection pattern. In this category may be included those surface features recently detected by the author with the aid of CO 2 abundance measurements over discrete areas of the planet in light reflected in the 1.05 μm band.

Temperature fluctuations in the solar photosphere

Solar photosphere temperature fluctuations from model consistent with convection hypothesis agreeing with limb darkening data

On the dynamical theory of polar wandering

A new approach to the dynamical theory of polar wandering and continental drift is outlined. This prospectus bases on the following hypotheses: 1. (1) The earth's outer shell, particularly the rigid lithosphere, is irregularly fractured, and the hypothesis of continental accretion is accepted; 2. (2) the earth's outer shell is heterogeneous, multilayered, and has low thermal conductivity, and there are lateral temperature variations in these layers; 3. (3) the hypothesis of mantle-wide, regular and cyclic thermal convection in the earth is rejected, and the asthenosphere-wide convection hypothesis is preferred; 4. (4) the generation of thermal energy in the earth is, or has been in excess of the energy removed by the surface heat flow; and 5. (5) the temperature at the earth's surface is approximately constant in time, and the earth's outer shell has never been “totally” molten since its formation. The outer shell refers to the uppermost 700 km layer of the earth with the upper 60 km as the lithosphere and the rest the asthenosphere. The thermoelasticity of the earth is briefly reviewed, and the thermoelastic energy storage in the outer shell is estimated as of the order of 10 35 ergs or higher, which is in conformity with the amount of excess thermal energy that may be accumulated in the earth during a geologic epoch. As the thermoelastic energy accumulates, the stress levels of the multiple layers in the outer shell rise accordingly, with differential expansion following. Within a geologic epoch, the stress difference in the lithosphere would reach its critical value, meanwhile the accumulated energy would also produce melting in the upper asthenosphere and then induce drastic changes in physical conditions to the surroundings. Because of the rigid, fractured and multilayered nature of the outer shell, catastrophic failures would occur before the upper asthenosphere was totally molten. These gigantic failures represent the major release of the disequilibrium energy in the earth and would occur repeatedly as the excess thermal energy continues to accumulate; so that all the basic geological phenomena are episodically induced. The immediate effect of the failure would be the excitation of polar wandering and a short-lived wobbling of the figure axis about the rotation axis, which might consequently produce torsion on the earth. The failure would also produce a torque on the earth which would force the lithosphere blocks to slide slowly over the asthenosphere relative with each other and thus result continental drift, orogenesis, epeirogenesis and other related phenomena. In the meantime, intense extrusion and intrusion of molten materials from the upper asthenosphere might immediately follow, which would “seal off” old geofractures and thus enlarge the continents. The after-failure tectonic activity would last a long time and a large amount of energy would thus be consumed. As the accumulated disequilibrium energy in the earth was greatly released, the earth would gradually return to its relatively quiescent period but, in the meantime, new energy accumulation would proceed for the next diastrophism. By and large, this dynamical prospectus may serve to interpret almost all the major geological puzzles observed.

Tectonics and continental drift

Interpretation of tectonic features through horizontal movements has opened the way to the idea of continental drift. Argand precedes Wegener. One should speak of continental-block drift rather than of continental drift. But this interpretation has been open to question. Gliding tectonics explain horizontal compressionand cover folding, resulting from a basement upheaval. The importance of the great transcurrents faults is that the horizontal displacements they prove are not subject to such discussion. One of the main facts brought out by tectonics is the chronology of the movements. The idea of individual, more or less world-wide, phases of discontinuous activity, should be discarded. The isostatic equilibrium of the crust is one of the most important facts to take into account. It is likely that the existence of the asthenosphere, inferred from vertical displacements, also makes horizontal movements possible. Isostatic equilibrium of the crust is consistent with any set of horizontal stresses, which must be the cause of horizontal deformations. Inquiry about the causes of such horizontal stresses leads only to very hypothetical conclusions. The best guide is the evaluation of the amount of energy involved. The energy produced by earthquakes if of the order of 1025 ergs/y, and the power needed to allow tectonic phenomena seems not to be much higher. Geothermal flow amounts to 1028 ergs/y. Thus, we can see how tectonic phenomena may derive their energy from geothermal flow. Two mechanisms have been suggested: contraction by cooling may build up stresses, but not provide the necessary amount of energy. But the convection current hypothesis seems to work. All the models of convection currents that have been considered share these two characteristics: (a) Between ascending and descending branches, the deviation of density or temperature from their mean value at the same depth are very small; thus, structure of the Earth as a whole may be studied without taking these deviations into account. (b) All these models involve velocities so small that inertia plays absolutely no part. I favour the idea that convection currents have been discontinuous, both in time and space.

Petrological evidence on temperature distribution in the mantle of the Earth

On the assumption that convection is an effective process of heat transfer in the mantle, petrological evidence suggests that the temperature at the core boundary fluctuates, in space and time, between a lower limit of about 1500°C and an upper limit of 2500°C. Generation of basaltic magma in the upper 100 km of the mantle is readily explained if the temperature gradient required to start convection does not exceed 0.6°/km, which is about twice the adiabatic value. Formation of uncommon magma types, such as anorthosites, may perhaps be explained by relatively small and momentary departures from conditions described. Implications of the convection hypothesis on the density distribution in the mantle are briefly discussed.

XXV. On an experiment bearing on the hypothesis of electrolytic convection in Geissler-tubes

XXV. <i>On an experiment bearing on the hypothesis of electrolytic convection in Geissler-tubes</i>