2005/03/17 by Wouter Bleeker · 4 citations
Earth and Planetary Sciences · Physics and Astronomy · #Paleontology and Stratigraphy of Fossils #Astro and Planetary Science #Planetary Science and Exploration
paper · doi:10.1017/cbo9780511536045.011
openalex publication_date 2005/03/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
It is proposed that Precambrian time should be subdivided into eons and eras that reflect natural stages in planetary evolution rather than being subdivided by a scheme based on numerical ages. The six eons can be briefly characterized as: 1. “Accretion and differentiation:” a time span of planet formation, growth, and differentiation up to the Moon-forming giant impact event. 2. Hadean (Cloud, 1972): an extended time span of intense bombardment and its consequences, but no preserved supracrustals. 3. Archean: an episode of increasing crustal record from the oldest supracrustals of Isua to the onset of giant iron formation deposition in the Hamersley Basin, likely related to increasing oxygenation of the atmosphere. 4. “Transition:” a time span with deposition of giant iron formations up to the first bona fide continental red beds. 5. Proterozoic: the time span of a nearly modern plate-tectonic Earth but without metazoan life. 6. Phanerozoic: Earth characterized by metazoan life forms of increasing complexity and diversity. INTRODUCTION The evolution of the geological time scale since the eighteenth century reflects in many ways the evolution of the geological sciences as a whole. On the one hand, the evolving time scale provides the essential nomenclature to classify, analyze, and communicate Earth history, while on the other it closely reflects the overall intellectual framework in which Earth history, as recorded in the rock record, is viewed.