Abundances of elements

When the universe was only a few minutes old, the temperature and density were high enough for nuclear fusion reaction to take place (Fig. 8.3). The formation of elements and isotopes, such as deuterium, isotopes of He, lithium, beryllium and boron, the Big Bang nucleosynthesis, is another indication for a hot Big Bang. The Big Bang theory predicts that in the early universe 24% He was produced. This was in the form of the stable He isotope (there are several reviews on that topic e.g. Olive, 1999 [253]). It is interesting to note that the production of this element is not strongly dependent on the density of matter in the universe. By density we mean here the value for the today s universe. Between the interval of density of matter from 10 to 10 kgm the He abundance remains very close to the value of 24%. 

The other elements and isotopes however sensitively depended on the density of normal matter in the universe. For example the amount of deuterium varies from 10 to 10 when the density runs from 10 to 10 kgm . The He abundance varies from 10 to 10 for the above mentioned density values. 

All observations are consistent with a density of these elements and isotopes as measured. So the distribution of the isotopes and elements leads to a value of 3 X 10 kg m for the average density of normal matter in the universe today. 

One has to stress again that no elements more massive than boron have been formed in the Big Bang. In this context we also mention dark matter. If dark matter consists of normal matter i.e. of protons and neutrons, then the density of protons and neutrons in the early universe would have been much higher and the resulting abundances of the light elements and isotopes mentioned would have been different from what we measure. A review about dark matter was given e.g. by Bertone, Hooper, and Silk, 2005 [26]. 

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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... 

Table 13.1 Abundances of elements in crustal rocks (g tonne )...

Abundance of elements in earth s crust, see Elements, abundance in earth s crust Acetaldehyde structure, 332 Acetamide, 338 Acetanilide, 344 Acetic acid in biochemistry, 428 structure, 333 Acetone... 

As can be seen in Fig. 2-1 (abundance of elements), hydrogen and oxygen (along with carbon, magnesium, silicon, sulfur, and iron) are particularly abundant in the solar system, probably because the common isotopic forms of the latter six elements have nuclear masses that are multiples of the helium (He) nucleus. Oxygen is present in the Earth s crust in an abundance that exceeds the amount required to form oxides of silicon, sulfur, and iron in the crust the excess oxygen occurs mostly as the volatiles CO2 and H2O. The CO2 now resides primarily in carbonate rocks whereas the H2O is almost all in the oceans. 

All biological chemistry is therefore limited by the abundance of elements, but especially by their availability on the Earth in its aqueous part, namely the oceans, which has changed with time. 

Cosmic abundances of elements and isotopes Table 3.3. Exponential curves of growth... 

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