Book contents
- Frontmatter
- Contents
- List of contributors
- Preface
- Acknowledgments
- List of abbreviations and acronyms
- Part I INTRODUCTION
- Part II CONCEPTS AND METHODS
- PART III GEOLOGIC PERIODS
- 9 The Precambrian: the Archean and Proterozoic Eons
- 10 Toward a “natural” Precambrian time scale
- 11 The Cambrian Period
- 12 The Ordovician Period
- 13 The Silurian Period
- 14 The Devonian Period
- 15 The Carboniferous Period
- 16 The Permian Period
- 17 The Triassic Period
- 18 The Jurassic Period
- 19 The Cretaceous Period
- 20 The Paleogene Period
- 21 The Neogene Period
- 22 The Pleistocene and Holocene Epochs
- Part IV SUMMARY
- Appendix 1 Recommended color coding of stages
- Appendix 2 Orbital tuning calibrations and conversions for the Neogene Period
- Appendix 3 Geomathematics
- Bibliography
- Stratigraphic Index
- General Index
10 - Toward a “natural” Precambrian time scale
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- List of contributors
- Preface
- Acknowledgments
- List of abbreviations and acronyms
- Part I INTRODUCTION
- Part II CONCEPTS AND METHODS
- PART III GEOLOGIC PERIODS
- 9 The Precambrian: the Archean and Proterozoic Eons
- 10 Toward a “natural” Precambrian time scale
- 11 The Cambrian Period
- 12 The Ordovician Period
- 13 The Silurian Period
- 14 The Devonian Period
- 15 The Carboniferous Period
- 16 The Permian Period
- 17 The Triassic Period
- 18 The Jurassic Period
- 19 The Cretaceous Period
- 20 The Paleogene Period
- 21 The Neogene Period
- 22 The Pleistocene and Holocene Epochs
- Part IV SUMMARY
- Appendix 1 Recommended color coding of stages
- Appendix 2 Orbital tuning calibrations and conversions for the Neogene Period
- Appendix 3 Geomathematics
- Bibliography
- Stratigraphic Index
- General Index
Summary
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.
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- A Geologic Time Scale 2004 , pp. 141 - 146Publisher: Cambridge University PressPrint publication year: 2005