The Earth formed from the same cloud of matter that formed the Sun, but the planets acquired different compositions during the formation and evolution of the solar system. The history of Earth caused parts of this planet to have differing concentrations of the elements.
Abundance of elements in Earth's crust
This graph illustrates the relative abundance of the chemical elements in Earth's upper continental crust.
Abundance (atom fraction) of the chemical elements in Earth's upper continental crust as a function of atomic number. Many of the elements shown in the graphic are classified into categories:
rock-forming elements
rare earth elements
major industrial metals
precious metals the nine rarest "metals" — the six platinum group elements plus Au, Re, and Te (a metalloid).
Note that there are two breaks where the unstable elements technetium (atomic number: 43) and promethium (atomic number: 61) would be. These are very rare, as on Earth they are only produced through the fission of heavy radioactive elements (for example, uranium or thorium). Both elements have been identified spectroscopically in the atmospheres of stars, where they are produced by ongoing nucleosynthetic processes. There are also breaks where the six noble gases would be as they are found in the Earth's crust due to decay chains from radioactive elements and are therefore not included. The six very rare, highly radioactive elements (polonium, astatine, francium, radium, actinium and protactinium) are not included, as their natural abundances are too low to have been accurately measured.
Oxygen and silicon are notably common; they form several common silicate minerals.
"Rare earth" element abundances
"Rare" earth elements is a historical misnomer; persistence of the term reflects unfamiliarity rather than true rarity. The more abundant rare earth elements are each similar in crustal concentration to commonplace industrial metals such as chromium, nickel, copper, zinc, molybdenum, tin, tungsten, or lead. Even the two least abundant rare earth elements (Tm, Lu) are nearly 200 times more common than gold. However, in contrast to ordinary base and precious metals, rare earth elements have very little tendency to become concentrated in exploitable ore deposits. Consequently, most of the world's supply of rare earth elements comes from only a handful of sources.
Differences in abundances of individual rare earth elements in the upper continental crust of Earth represent the superposition of two effects, one nuclear and one geochemical. First, rare earth elements with even atomic numbers (58Ce, 60Nd, ...) have greater cosmic and terrestrial abundances than adjacent rare earth elements with odd atomic numbers (57La, 59Pr, ...). Second, the lighter rare earth elements are more incompatible (because they have larger ionic radii) and therefore more strongly concentrated in the continental crust than the heavier rare earth elements. In most rare earth deposits, the first four rare earth elements - La, Ce, Pr, and Nd - constitute 80 to 99% of the total.
Ocean
Elemental composition of Earth's ocean water (by mass) Element Percent Element Percent
Oxygen 85.84 Sulfur 0.091
Hydrogen 10.82 Calcium 0.04
Chlorine 1.94 Potassium 0.04
Sodium 1.08 Bromine 0.0067
Magnesium 0.1292 Carbon 0.0028
See sea water for abundance of elements in the ocean, but note that that list is by mass - a list by molarity (mole-fraction) would look very different for the first 4 elements; specifically, hydrogen would comprise nearly two-thirds of the number of all atoms because hydrogen itself comprises two of the three atoms of all water molecules.
Atmosphere
The order of elements by volume-fraction (which is approximately molecular mole-fraction) in the atmosphere is nitrogen (78.1%), oxygen (20.9%), argon (0.96%), followed by (in uncertain order) carbon and hydrogen because water vapor and carbon dioxide which represent most of these two elements in the air are variable components. Sulfur, phosphorus, and all other elements are present in significantly lower proportions.
According to the above graphic, argon, a significant if not major component of the atmosphere, does not appear in the crust at all because argon, an inert gas, cannot remain within the crust.
Human body
By mass, human cells consist of 65-90% water (H2O), and a significant portion is composed of carbon-containing organic molecules. Oxygen therefore contributes a majority of a human body's mass, followed by carbon. 99% of the mass of the human body is made up of the six elements oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.
Element Percent by mass
Oxygen 65
Carbon 18
Hydrogen 10
Nitrogen 3
Calcium 1.5
Phosphorus 1.2
Potassium 0.2
Sulfur 0.2
Chlorine 0.2
Sodium 0.1
Magnesium 0.05
Iron, Cobalt, Copper, Zinc, Iodine <0.05 each
Selenium, Fluorine <0.01 each