{{redirect|Azoic|the band|The Azoic}}
'''Azoic Age''', '''Azoic Era''', '''Azoic Period''' and '''Azoic Eon''' were terms used before 1950 to describe the age of rocks formed before the appearance of life in the geologic sequence. The word "Azoic" is derived from the Greek ''a-'' meaning without and ''zoön'' meaning animal (or living being), meaning ''without life''. This name was given because rocks from this era were first thought to possess no fossil record.<ref name="Dana-1863">[https://books.google.com/books?id=QjwDAAAAQAAJ 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];</ref><ref name="USGS-1925">[https://books.google.com/books?id=bGOJ5XQNKc0C&q=azoic 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];</ref><ref name=":0">{{Cite book |last=Toghill |first=Peter |title=The Geology of Britain: An Introduction |publisher=Swan Hill Press |year=2000 |isbn=9781853108907 |pages=33}}</ref><ref>{{Cite web |title=AZOIC Definition & Meaning {{!}} Dictionary.com |url=https://www.dictionary.com/browse/azoic |access-date=2026-03-20 |website=www.dictionary.com}}</ref>
Azoic was used as early as 1846 by a geologist named Adams,<ref name="PreC">[https://books.google.com/books?id=36cPAAAAIAAJ&q=azoic Leith, Charles Kenneth and Van Hise, Charles Richard (1909) ''Pre-Cambrian Geology of North America'' United States Geological Survey, Washington, DC, p.58];</ref> and gradually replaced the earlier term ''Primitive''.<ref name="PreC"/> Due to the controversy over evolution, "Azoic" was replaced, by 1900, in most usages by the term "Archaean" or "Archaeozoic<ref name="PreC2">[https://books.google.com/books?id=36cPAAAAIAAJ&q=azoic Leith, Charles Kenneth and Van Hise, Charles Richard (1909) ''Pre-Cambrian Geology of North America'' United States Geological Survey, Washington, DC, p.61];</ref> The Archaean was later subdivided into the Archaean and the even earlier Hadean. Many of the rocks that had originally been thought to be of Azoic time were reclassified as Archaean, but the period itself is now essentially the Hadean.
J.D. Dana in 1863, wrote 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 also wrote that when fossils had been found in strata which had previously been classified as Azoic, the boundary was simply moved lower.<ref name="Dana-1863b">[https://books.google.com/books?id=QjwDAAAAQAAJ 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];</ref>
== Reclassification == The oldest fossils, found in what was previously called Azoic rock, established the geological boundary between the Precambrian and Cambrian. These terms have thereby supplanted "Azoic".<ref name=":0" /><ref>{{Cite web |title=GEOL 102 Introduction to the Strange Aeons of the Precambrian: The Hadean Eon |url=https://www.geol.umd.edu/~tholtz/G102/lectures/102hadean.html |access-date=2026-03-20 |website=www.geol.umd.edu}}</ref>
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Category:Geologic time scales of Earth