Azoic Age

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Azoic Time, Age, Era or Eon was a term used before 1950 to describe the age of rocks that were formed before the appearance of life in the geologic sequence. It has had various definitions. Although the word is derived from the Greek "a-" meaning without and "zoo" meaning animal, it was first used to mean without life.^[1][2]

Azoic was used as early at 1846 by a geologist named Adams,^[3] and gradually replaced the earlier term Primative.^[3] Due to the controversy over evolution, Azoic was replaced, by 1900, in most usage by the term Archean.^[4]. The Archean was later subdivided into the Archean and the Hadean. Many of the rocks that had originally been thought to be of Azoic time ended up being classified as Archeozoic.

Dana in 1863, said that the Azoic "stands as the first [age] in geologic history, whether science can point out unquestionably the rocks of that age or not." He went on to say that when fossils had been found in strata which had previously been classified as Azoic, the boundary was simply moved lower. "Such changes are part of the progress of the science."^[5]

[edit] Notes

1. ^ Dana, James Dwight (1863) Manual of geology: Treating of the Principles of the Science with Special Reference to American geological history, for the use of colleges, academies, and schools of science T. Bliss & Co., Philadelphia, p.130;
2. ^ Wilmarth, M. Grace (1925) The Geologic Time Classification of the United States Geological Survey Compared with Other Classifications United States Geological Survey, Washington, DC, pp 18, 20;
3. ^ ^{a b} Leith, Charles Kenneth and Van Hise, Charles Richard (1909) Pre-Cambrian Geology of North America United States Geological Survey, Washington, DC, p.58;
4. ^ Leith, Charles Kenneth and Van Hise, Charles Richard (1909) Pre-Cambrian Geology of North America United States Geological Survey, Washington, DC, p.61;
5. ^ Dana, James Dwight (1863) Manual of geology: Treating of the Principles of the Science with Special Reference to American geological history, for the use of colleges, academies, and schools of science T. Bliss & Co., Philadelphia, p.134;