earth (geology)

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geology and other Earth sciences The word ‘geology’ is derived from two Greek words (geó, logió) and translates literally as the study or science of the Earth. The word was coined in medieval Latin in the eighth century by the Northumbrian monastic scholar and historian Bede (‘The Venerable Bede’) to mean the study of things earthly as opposed to the study of things godly (i. e. theology). In the late eighteenth century it acquired something like its modern meaning of scientific observation of the Earth, its structure, composition, and history. Subsequently, various related disciplines emerged, such as palaeontology, the study of fossils; mineralogy, the study of minerals; geomorphology, the study of landscapes; geochemistry, the study of the behaviour of chemical elements within the Earth and the associated analytical techniques; and geophysics, the investigation of the Earth's magnetic, electrical, and gravitational fields, and their use, along with the propagation of seismic waves, to probe the planet's interior. This left the meaning of ‘geology’ impoverished in scope, with a geologist being defined as someone who investigated the Earth primarily by seeking to interpret rocks and the settings in which they formed.

The term ‘Earth sciences’ came into vogue during the 1960s and 1970s as an inclusive expression that was intended to embrace geology and all its related disciplines. Geologists, geophysicists, and geochemists often restrict the meaning of ‘Earth sciences’ pretty much to just those three disciplines, but in other contexts (as in this Companion) the term is much wider in scope, embracing even such fields as geodesy (the science of measuring and mapping the surface of the Earth), oceanography (the study of the oceans), meteorology (the study of the atmosphere), and sometimes even anything that could be described as geography.

The term ‘planetary sciences’ is used to describe the application of the techniques of ‘Earth sciences’ (in either the broader or the narrower sense) for the study of planets other than the Earth, or of planets in general. It is ironic that the more modern invention ‘Earth sciences’ should have proved inadequate to the task of describing the extension of the science beyond our home planet, and that people are beginning to use ‘geology’ to cover any or all related disciplines employed on any Earth-like body. For example ‘lunar geology’ and ‘martian geology’ have now ousted their more abstruse equivalents ‘selenology’ and ‘areology’. This is perfectly justifiable, because in the original Greek ‘geo’ can carry the connotation of any Earth-like body rather than the Earth alone.

David A. Rothery

Bibliography

Rothery, D. A. (1997) Teach yourself geology. Hodder and Stoughton, London.

earth in chemistry, metallic oxide not readily reducible by chemical means, e.g., alkaline earths , rare earths , and alumina . The name is also applied to certain absorbent clays, e.g., fuller's earth , and to other compounds, e.g., carbonates, silicates, or hydroxides. Many earths were once thought to be elements . A. L. Lavoisier was first to suspect that they might be compounds of more basic elements. Earth was one of the four "roots" of the Greek philosopher Empedocles, the other three being air, water, and fire. These substances were first called elements ( stoicheia ) by Plato.