Abundance of elements in the Earth's crust
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Major Elements in the Earth's Crust: Abundance and Distribution
The Earth's crust is primarily composed of a small group of elements. Oxygen and silicon are by far the most abundant, together making up the majority of the crust's mass. Following these, aluminum, iron, calcium, sodium, potassium, and magnesium are the next most common elements, and these eight elements account for nearly 99% of the crust's total mass 17. The dominance of silicate minerals, which are built from silicon and oxygen, explains this distribution .
Quantitative Estimates of Elemental Abundance
Multiple studies have compiled and revised tables of elemental abundances in the Earth's crust. For example, estimates based on igneous rocks, which make up about 95% of the crust by volume, show that oxygen constitutes roughly 46% by weight, silicon about 28%, aluminum 8%, iron 5%, calcium 4%, sodium 2.5%, potassium 2.5%, and magnesium 2% 17. These values are consistent across various compilations, though minor differences exist due to the inclusion or exclusion of sedimentary and oceanic rocks 12.
Trace Elements and Rare Earth Elements in the Crust
While the major elements dominate, trace elements such as lithium, chromium, nickel, and rare earth elements are present in much smaller amounts but are important for understanding crustal processes and resource distribution. Recent studies using advanced analytical techniques have provided updated values for these trace elements. For example, the upper continental crust contains about 41 ppm lithium, 73 ppm chromium, and 34 ppm nickel, with rare earth elements like lanthanum at 31 ppm and thulium at 0.32 ppm 410. These values are based on correlations in sedimentary rocks and provide a more accurate picture of trace element distribution 410.
Regional and Tectonic Variations in Elemental Abundance
The composition of the crust varies between continental and oceanic regions, as well as between different tectonic settings such as shields, folded belts, and oceanic crust. Regional geochemical methods have been used to estimate the abundance of elements in these different units, showing that the so-called "average crust" often reflects the continental crust more than the global crust, which includes oceanic regions . This distinction is important for understanding the global cycling of elements and the distribution of natural resources .
Iron: Abundance in the Crust Versus the Whole Earth
Iron is a special case: while it is only the fourth most abundant element in the crust (about 5% by weight), it is the most abundant element in the entire Earth, making up about 35% of the planet's mass due to its concentration in the core 78. In the crust, iron is mostly found in silicate and oxide minerals, and its abundance is much lower compared to its overall presence in the planet 78.
Updates and Revisions in Elemental Abundance Tables
Advances in analytical methods, such as spectrographic analysis and ICP-MS, have led to revisions in the estimated abundances of several elements, especially those that are present in very low concentrations like gallium, germanium, indium, and thallium 14. These updates are important for refining models of crustal composition and for applications in geochemistry and resource exploration .
Conclusion
The Earth's crust is dominated by a handful of elements, with oxygen and silicon being the most abundant. Trace elements, though present in much smaller amounts, are crucial for understanding geological processes and resource distribution. Ongoing research and improved analytical techniques continue to refine our understanding of the abundance and distribution of elements in the Earth's crust, highlighting both the consistency of major element patterns and the importance of regional and methodological differences in trace element estimates 124710.
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