This is a plot of the elemental abundances in the earth's crust. As is usual in geochemistry, the abundance of silicon has been set at 10⁶, or Log(Si) = 6.0. This abundance pattern is markedly different from SAD, "solar," or "cosmic." Note the following points:

• Hydrogen is less abundant than oxygen, silicon, or magnesium. Most of the hydrogen is in water, so the hydrogen complement for the bulk earth would be even smaller.
• Helium, and the noble gases (neon, argon, xenon) are greatly depleted. This is true of the bulk earth composition as well, and is one of the more powerful arguments that the earth's atmosphere was never a significant fraction of the mass of the planet. Early have speculations about the history of the earth's atmosphere considered the possibility that huge amounts of hydrogen and helium could have escaped. This might have been the case for these light elements, but large amounts of the heavier noble gases would not have escaped. Their molecular weight is too high. It is therefore plausible to assume they were never present in more than trace amounts.
• There are depletions of neighboring elements such as Ru, Rh, and Pd, or Re through Au. These elements are called siderophiles by geochemists. The word means "iron loving." They are depleted in the earth's crust because they associate with iron in its metallic or reduced form. They are presumably enriched in the core.
• There are numerous places where the sawtooth pattern of the SAD is distorted. The ubiquitous tendency of even-Z elements to be more abundant than their odd-Z neighbors in the SAD is the result of nuclear properties. The crustal abundance results from the chemical properties of the elements.
• The sawtooth pattern does persist among the lanthanide rare earths, the elements from La through Yb. This is because these elements have very similar chemical properties. The nuclear pattern has persisted even though the abundances of these elements is very different in the crust from what it is in the SAD.