The crust is the outermost layer of the solid Earth and composed of two major types of rocks: the oceanic crust and the continental crust. The abundance of crustal rocks varies with location and depth, but can be measured in parts per million (ppm) or billion (ppb). The continental crust contains about 98 percent of the Earths crustal rocks, and is generally the oldest, thickest, and hardest rock formation.
In terms of abundance, the principal elements of continental crust rocks when weighed on a global scale are oxygens (46.60%), silica (27.72%), and aluminum (8.13%). These three rocks are also the most abundant in oceanic crust rocks as well. The abundance of elements in the crust depends on the chemical composition, which is derived from two main sources: (1) material that was returned to the Earth either through chemical weathering of older rocks or recycling of previously created rocks, and (2) the material condensed and cooled from the primordial solar nebula which gave birth to the solar system.
The oceanic crust, on the other hand, is a relatively thin layer of rock (∼7 km thickness, divided into two layers) located beneath the ocean basins. It is primarily composed of silicates and basalts. These rocks are much younger than the continental rocks, and are more mafic (or low-silica) compared to the continental rocks. The most abundant elements in oceanic crust rocks, when weighed on a global scale, are oxygens (45.6%), silica (23.8%) and magnesium (10.5%).
The abundance of elements in the mantle — the layer beneath the crust — also varies with location and depth. Generally, the mantle is composed of peridotite, which is a type of rock composed of olivine and pyroxenes with minor concentrations of other minerals. When measured on a global scale, the most abundant elements in peridotite are oxygens (44.6%), magnesium (34.8%), silica (17.3%), and iron (3.38%).
The abundance of elements in the Earths core is not very well known due to the difficulty of measuring the element composition of solid metal in the core. However, it is widely accepted that the core consists mostly of iron (90%-95%), with small amounts of nickel and possibly some other elements.
The abundance of elements in Earths crust is an important factor in understanding and predicting plate tectonic processes, climate, and other aspects of Earths geology. It is essential to understand the abundance of each element in Earths crust and mantle in order to understand how it affects global geochemical cycles. Knowing the abundance of each element in Earths crust and mantle is also important to understanding the origin and evolution of our planet.
