Chemistry

Geochemistry

Geochemistry is the branch of Earth Science that applies chemical principles to deepen an understanding of the Earth system and systems of other planets.  Because radioactive isotopes decay at measurable and constant rates (e.g., half-life) that are proportional to the number of radioactive atoms remaining in the sample, analysis of rocks and minerals can also provide reasonably accurate determinations of the age of the formations in which they are found. Geochemistry generally concerns the study of the distribution and cycling of elements in the crust of the earth. Just as the biochemistry of life is centered on the properties and reaction of carbon, the geochemistry of Earth's crust is centered upon silicon. Also important to geochemistry is oxygen .Oxygen is the most abundant element on Earth. Together, oxygen and silicon account for 74% of Earth's crust. The eight most common elements found on Earth, by weight, are oxygen (O), silicon (Si), aluminium (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg). Except in acid or siliceous igneous rocks containing greater than 66% of silica, known as felsic rocks, quartz is not abundant in igneous rocks. In basic rocks (containing 20% of silica or less) it is rare for them to contain as much silicon, these are referred to as mafic rocks. If magnesium and iron are above average while silica is low, olivine may be expected; where silica is present in greater quantity over ferromagnesian minerals, such as augite, hornblende, enstatite or biotite, occur rather than olivine. The effects of acid rain are of great concern to geologists not only for the potential damage to the biosphere, but also because acid rain accelerates the weathering process. Precipitation of this "acid rain" adversely affects both geological and biological systems