Origin of elements, molecules and the earth

Our galaxy is probably 13.7 0.2 Gyr old and was formed by the hot Big Bang, assuming that the whole mass of the galaxy was concentrated in a primordial core. Based on the principles of physics, it is assumed that density and temperature were 

The most abundant elements (Fig. 2.2) up to Fe are multiples of He ( C, O, Mg, Si, etc.). During the red giant phase of stellar evolution, free neutrons are generated which can interact with all nuclei and build up all the heavy elements up to Bi all nuclides with the atomic number 84 are radioactive. Recently (2003) it has been found that even ° Bi decays, but extremely slowly (Ti/2 = 1.9 10 yr). The build-up of elements of every known stable isotope depends on different conditions of density and temperature. Thus, the production process required cycles of star formation, element formation in stellar cores, and ejection of matter to produce a gas enriched with heavy elements from which new generations of stars could form. The synthesis of material and subsequent mixing of dust and gas between stars produced the solar mix of elements in the proportions that are called cosmic abundance (Fig. 2.2 and cf Table 2.13). 

In addition to stable elements, radioactive elements are also produced in stars. There are four natural radioactive decay series Th (Ti/2 = 1.405 10 yr), 

The Milky Way, sometimes called simply the Galaxy , is the galaxy in which our solar system is located. It is extremely difficult to define when the Milky Way formed, but the age of the oldest star in the Galaxy yet discovered, HE 1523-0901, is estimated to be about 13.2 Gyr, nearly as old as the Universe itself (Frebel 2007). 

The region between the stars in a galaxy, termed the interstellar medium, has very low densities, but is filled with gas, dust, magnetic fields, and charged particles. 

---