Cosmochemistry: Unveiling the Universe's Origin and Evolution

In the Beginning

Certain questions about our existence on Earth are so fundamental that they have been incorporated into religious mythologies. These questions not only concern the origin of the Earth and the evolution of life but also extend to the origin of the universe and to the nature of space and time. Did the universe have a beginning, and will it ever end? What existed before the universe formed? Does the universe have limits, and what exists beyond those limits? It is proper to raise these questions at the beginning of a geochemistry course because they are within the scope of cosmochemistry.

The Big Bang

The universe started like a bubble in a stream. At first, it was not there, and suddenly it formed and expanded rapidly as though it were exploding (Gott, 1982). Science has its share of practical jokers who immediately referred to the start of the expansion of the universe as the Big Bang (Gamow, 1952). From the very beginning, the universe had all of the mass and energy it contains today. As a result, its pressure and temperature, say 10^-32 seconds after the Big Bang, were so high that matter existed in its most fundamental form as "quark soup." As the universe expanded and cooled, the quarks combined to form more familiar nuclear particles that ultimately became organized into nuclei of hydrogen and helium.

Formation of atomic nuclei began about 13.8 seconds after the Big Bang when the temperature of the universe had decreased to 3 x 10⁹ K. This process continued for about 30 minutes but did not go beyond helium because the nuclear reactions could not bridge a gap in the stabilities of the nuclei of lithium, beryllium, and boron. At that time, the universe was an intensely hot and rapidly expanding fireball.

Some 700,000 years later, when the temperature had decreased to about 3 x 10³ K, electrons became attached to the nuclei of hydrogen and helium. Matter and radiation were thereby separated from each other, and the universe became transparent to light. Subsequently, matter began to be organized into stars, galaxies, and galactic clusters as the universe continued to expand to the present time (Weinberg, 1977).

But how do we know all this? The answer is that the expansion of the universe can be seen in the "red shift" of spectral lines of light emitted by distant galaxies, and it can be "heard" as the "cosmic microwave radiation," which is the remnant of the fireball that still fills the universe. In addition, the properties of the universe immediately after the Big Bang were similar to those of atomic nuclei. Therefore, a very fruitful collaboration has developed among nuclear physicists and cosmologists that has enabled them to reconstruct the history of the universe back to about 10^-32 seconds after the Big Bang. These studies