<P> In geology, the term' sial' refers to the composition of the upper layer of the Earth's crust, namely rocks rich in silicates and aluminium minerals . It is sometimes equated with the continental crust because it is absent in the wide oceanic basins, but "sial" is a geochemical term rather than a plate tectonic term . As these elements are less dense than the majority of the earth's elements, they tend to be concentrated in the upper layer of the crust . </P> <P> Geologists often refer to the rocks in this layer as felsic, because they contain high levels of feldspar, an aluminium silicate mineral series . However, the sial "actually has quite a diversity of rock types, including large amounts of basaltic rocks ." </P> <P> The name' sial' was taken from the first two letters of silica and of alumina . The sial is often contrasted to the' sima,' the next lower layer in the Earth, which is often exposed in the ocean basins; and the nickel - iron alloy core, sometimes referred to as the "Nife". These geochemical divisions of the Earth's interior (with these names) were first proposed by Eduard Suess in the 19th century . This model of the outer layers of the earth has been confirmed by petrographic, gravimetric, and seismic evidence . </P> <P> Sial has a lower density (2700--2800 kg / m) than sima, which is primarily due to increased amounts of aluminium, and decreased amounts of iron and magnesium . The base of the sial is not a strict boundary, the sial grades into the denser rocks of the sima . The Conrad discontinuity has been proposed as the boundary, but little is known about it, and it doesn't seem to match the point of geochemical change . Instead, the boundary has been arbitrarily set at a mean density of 2800 kg / m . </P>

Who divided the interior of the earth into 3 zones sial sima nife