Chapter 1 : Introduction 1. 1 Geochemistry

By White, W. M.

Description
Physics Literature

Excerpt
Excerpt: Geochemistry has flourished in the quantitative approach that has dominated earth science in the second half of the twentieth century. This quantitative approach has produced greater advances in the understanding of our planet in the last 50 years than in all of prior human history. The contributions of geochemistry to this advance have been simply enormous. Much of what we know about how the Earth and the Solar System formed has come from research on the chemistry of meteorites. Through geochemistry, we can quantify the geologic time scale. Through geochemistry, we can determine the depths and temperatures of magma chambers. Through geochemistry, mantle plumes were recognized. Through geochemistry, we know that sediments can be subducted into the mantle. Through geochemistry, we know the temperatures and pressures at which the various metamorphic rock types form and we can us this information, for example, to determine the throw on ancient faults. Through geochemistry, we know how much and how fast mountain belts have risen. Through geochemistry, we are learning how fast they are eroding. Through geochemistry, we are learning how and when the Earth?s crust formed. Through geochemistry, we are learning when the Earth?s atmosphere formed and how it has evolved. Through geochemistry, we are learning how the mantle convects. Through geochemistry, we are learning how cold the ice ages were and what caused them. The evidence of the earliest life, 3.8 giga years (billion, or 109 years, which we will henceforth abbreviate as Ga), is not fossilized remains, but chemical traces of life. Similarly, the tenuous evidence that life existed on Mars about the same time is also largely chemical. Not surprisingly, instruments for chemical analysis have been key part of probes sent to other heavenly bodies, including Venus, Mars, Jupiter. Geochemistry lies at the heart of environmental science and environmental concerns. Problems such as acid rain, the ozone hole, the greenhouse effect and global warming, water and soil pollution are geochemical problems. Addressing these problems requires a knowledge of geochemistry. Similarly, most of our non-renewable resources, such as metal ores and petroleum, form through geochemical processes. Locating new sources of these resources increasing requires geochemical approaches. In summary, every aspect of earth science has been advanced through geochemistry.