Relative Abundance of Elements

The most abundant element in the universe is the lightest element—hydrogen—followed by the second lightest element—helium. The Sun, for example, is about three-fourths hydrogen, one-fourth helium, and has only traces of all the other elements. 

On Earth, the most abundant elements are oxygen, which is almost 21 percent of the atmosphere by volume and almost 46 percent of Earth s crust by mass and silicon, which is about 27 percent of Earth s crust. Together, oxygen and silicon comprise about 73 percent of Earth s crust. This should not be too surprising, considering that quartz and sand (which is just decomposed quartz) are made of oxygen and silicon, and both substances are widespread throughout the world. 

The next most abundant elements on Earth are aluminum, iron, calcium, magnesium, sodium, and potassium, which together make up about 26 percent of Earth s crust, with a large amount of sodium and potassium also found in seawater. Their abundance in part explains why their names should sound so familiar. Of course, other reasons for their familiar names include the widespread use of aluminum and iron in today s economy, plus the fact that iron, calcium, magnesium, sodium, and potassium are some of the elements that are essential to human health. 

The most abundant elements in Earth s crust are o)ygen, which constitutes almost one-half of the crust, and silicon, which constitutes more than one-quarter. The least abundant naturally occurring elements in Earth s crust are ruthenium and rhodium-both exist at concentrations of about 0.1 ppb. 

The elements listed so far constitute about 99 percent of Earth s crust. That means all the remaining naturally occurring elements together constitute the remaining 1 percent Compared to the eight most abimdant elements, most of the remaining elements are found in only a small amount on Earth. 

---

Because of the long time scale involved in the s-process, unstable nuclides formed by (n.y) reactions have time to decay subsequently by decay (electron emission). The crucial factor in determining the relative abundance of elements... 

The sun is not a "perfect" radiator, nor does it have uniform composition. The sun is composed of about 92% hydrogen, 7.8% helium. The remaining 0.2% of the sun is made up of about 60 other elements, mainly metals such as iron, magnesium, and chromium. Carbon, silicon, and most other elements are present as well.1 The inte raction of the atoms and ions of these elements with the radiation created by the annihilation of matter deep within the sun modifies and adds structure to the solar spectral distribution of energy. Astrophysicists such as Kurucz have used quantum calculations and the relative abundance of elements in the sun to compute the theo retical spectral distribution from first principles.5 Figure 1 shows a plot of the Kurucz computed spectral distribution at very high resolution (0.005 nanometer at UV) as well as an inset showing much lower resolution (0.5 nanometer in UV to 5 nm in IR) plot. 

Fig. 1.1 The cosmic abundance of elements. The relative abundance of elements (vertical axis) is defined as the number of atoms of each element per 106 atoms of silicon and is plotted on a logarithmic scale.

Fig. 1 The relative abundance of elements in the earth s crust illustrates the common availability of quartz and the silicas [1]...

The composition of the Earth was determined both by the chemical composition of the solar nebula, from which the Sun and planets formed, and by the nature of the physical processes that concentrated materials to form planets. The bulk elemental and isotopic composition of the nebula is believed or usually assumed to be identical to that of the Sun. The few exceptions to this include elements and isotopes such as lithium and deuterium that are destroyed in the bulk of the Sun s interior by nuclear reactions. The composition of the Sun as determined by optical spectroscopy is similar to the majority of stars in our galaxy and, accordingly, the relative abundances of elements in the Sun are referred to as "cosmic abundances". Although the cosmic abundance pattern is commonly seen in other stars, there are dramatic exceptions, such as stars composed of iron or solid nuclear matter, as is the case with neutron stars. The best estimation of solar abundances is based on data from optical spectroscopy and meteorite studies and in some cases extrapolation and nuclear theory. The measured solar abundances are listed in Fig. 2-1 and Table 2-1. It is believed to be accurate to about 10% for the majority of elements. The major features of the solar abundance distribution are a strong decrease in the abundance of heavier elements, a large deficiency of Li, Be, and B, and a broad abundance peak centered near Fe. The factor of 10 higher... 

Hydrogen overwhelmingly is the most abundant element in the universe. Stars are composed mostly of hydrogen, followed by helium and only very small amounts of any other element. Relative abundances of elements can be expressed in parts per million, either by mass or by numbers of atoms. 

Table 7-lb. Average Absolute and Relative Abundances of Major Elements in Crustal Rock, Soil, and Shale-, Relative Abundances of Elements in Fly Ash from Coal and Fuel-Oil Combustion and Relative Abundances of Major Elements in the Remote Continental Aerosol, with Enrichment Factors (Aerosol) EF= (X)/(AI)aeroso,/(X)/(AI)crusta, rock ... 

Below is a table listing the relative abundance of elements in the Sun. In total there are at least sixty-seven elements that have been identified as being present in the Sun— this table lists the ten most abundant ones. 

FIGURE P.2 Left the (relative) abundance of elements in Universe right the planets differentiation in our solar system according to the (relative) abundance of atmosphere, silicates and metals after [Mineralogy (2001). Lectures Notes of Mineralogy, University of Bristol (Curator Prof D. M. Sherman)]. 

Figure 21.21 Relative abundance of elements 1-10 in the solar system. Note the logarithmic scale used for the y-axis. 

FIGURE 10.7 Relative abundance of elements in the solar system, includuig contributions from meteorites. Reproduced from PA. Cox, The Elements, Oxford University Press, Oxford, 1989, figure from p. 17 (with permission). 

---