Seismic Evidence for Partial Melt at the Base of Earth's Mantle

Quentin Williams,Edward J Garnero

doi:10.1126/science.273.5281.1528

Abstract

The presence of an intermittent layer at the base of Earth's mantle with a maximum thickness near 40 kilometers and a compressional wave velocity depressed by ∼10 percent compared with that of the overlying mantle is most simply explained as the result of partial melt at this depth. Both the sharp upper boundary of this layer (<10 kilometers wide) and the apparent correlation with deep mantle upwelling are consistent with the presence of liquid in the lowermost mantle, implying that the bottom of the thermal boundary layer at the base of the mantle may lie above its eutectic temperature. Such a partially molten zone would be expected to have enhanced thermal and chemical transport properties and may provide constraints on the geotherm and lateral variations in lowermost mantle temperature or mineralogy.

Highlights

STATEMENT OF THE PROBLEMThe Earth core made of solid iron and nickel contains hydrogen in an amount that significantly influences the endogenous life of the planet in a variety of aspects
Based on the assumption that the total content of iron and nickel in the outer core amounts to 90 %, and calculations with reference to the content of iron viewed as the main component of the core, we find that the mass of iron in the outer core is 1.66×1027 g
According to the available experimental data, there is a high probability that hydrogen in the outer liquid core of the Earth is contained in the hydride form

Summary

Introduction

The Earth core made of solid iron and nickel contains hydrogen in an amount that significantly influences the endogenous life of the planet in a variety of aspects. This problem is among the top and, at the same time, most controversial issues of geochemistry, geophysics, petrology and geotectonics. The problem was stated by V.I. Vernadsky who stated that conditions of the Earth interior are favorable “for the existence of hydrogenous bodies..., including hydrogen solutions in metals” [Vernadsky, 1960, p. Vernadsky who stated that conditions of the Earth interior are favorable “for the existence of hydrogenous bodies..., including hydrogen solutions in metals” [Vernadsky, 1960, p. Today the main reason for skepticism about the possibility of the presence of hydrogen in the center of the Earth is a lack of any answer to the question of how to explain this presence, bearing in mind the fact that molecular hydrogen is extremely highly volatile

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