General Elemental Abundances in Earth
Earth with a mass of approximately 6◊10^24 kg is composed mostly of iron (32%), oxygen (30%), silicon (15%), magnesium (14%), sulfur (2.9%), nickel (1.8%), calcium (1.5%) and aluminium (1.4%). Distribution of elements in different parts of Earth isnít homogeneous. As a result of mass segregation, Earth can chemically be divided into the crust, upper mantle, lower mantle, outer core, and inner core. The core region is estimated to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements. The chemical composition of the mantle has been difficult to determine with a high degree of certainty as a result of its inaccessibility. Based on rocks originating from the uppermost mantle, composition of the Earth's upper mantle is estimated to be mainly SiO2 (45%), MgO (39%), FeO (8.2%), Al2O3 (4%) and CaO (3.2%). Over 99% of the crust is composed of 11 oxides, principally silica, alumina, iron oxides, lime, magnesia, potash, and soda.
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The numbers in the above image are from Morgan, J. W.; Anders, E. (1980). "Chemical composition of Earth, Venus, and Mercury". Proceedings of the National Academy of Sciences. In this reference, other notable elemental abundances in earth expressed in ppm (parts per million by mass) are as follows Cr (4120), P (1920), Na (1250), Co (840), Ti (820), Nb (800) and Mn (750).