The mantle constitutes the largest internal subdivision of the Earth by both mass and volume, and extends from the Moho, at a mean depth of about 21 km, to the core-mantle boundary at a depth of 2891 km. On a gross scale it is believed to be chemically homogeneous, apart from the abundances of minor and trace elements, and formed of silicate minerals. The mineralogy and structure of the silicates change with depth and give rise to a transition zone between 410 and 660 km depth, which separates the upper and lower mantle.
Mantle materials are only rarely brought to the surface, in ophiolite complexes (Section 2.5), in kimber-lite pipes (Section 13.2.2), and as xenoliths in alkali basalts. Consequently, most of our information about the mantle is indirect and based on the variation of seismic velocities with depth combined with studies of mineral behavior at high temperatures and pressure, and in shock-wave experiments. Geochemical studies of meteorites and ultramafic rocks are also utilized in making predictions about the mantle.
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Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.