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Pure and Applied Chemistry

The Scientific Journal of IUPAC

Ed. by Burrows, Hugh / Weir, Ron / Stohner, Jürgen

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IUPAC-IUGS common definition and convention on the use of the year as a derived unit of time (IUPAC Recommendations 2011)

Norman E. Holden1 / Mauro L. Bonardi1 / Paul De Bièvre4 / Paul R. Renne5 / Igor M. Villa8

1International Union of Pure and Applied Chemistry

2National Nuclear Data Center, Brookhaven National Laboratory, Upton, NY 11973, USA

3LASA, Università degli Studi di Milano and INFN, I-20090 Segrate, Italy

4Consultant on Metrology in Chemistry, Duineneind 9, B-2460 Kasterlee, Belgium

5Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94720, USA

6Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA

7International Union of Geological Sciences

8Institut für Geologie, Universität Bern, CH-3012 Bern, Switzerland

9Università di Milano Bicocca, I-20126 Milano, Italy

Project Year: 2006, Project Code: 2006-016-1-200

Citation Information: Pure and Applied Chemistry. Volume 83, Issue 5, Pages 1159–1162, ISSN (Online) 1365-3075, ISSN (Print) 0033-4545, DOI: 10.1351/PAC-REC-09-01-22, April 2011

Publication History

Published Online:

The units of time (both absolute time and duration) most practical to use when dealing with very long times, for example, in nuclear chemistry and earth and planetary sciences, are multiples of the year, or annus (a). Its proposed definition in terms of the SI base unit for time, the second (s), for the epoch 2000.0 is 1 a = 3.1556925445 × 107 s. Adoption of this definition, and abandonment of the use of distinct units for time differences, will bring the earth and planetary sciences into compliance with quantity calculus for SI and non-SI units of time.

Keywords: annus; decay constants; geochronology; IUPAC Analytical Chemistry Division; IUPAC Inorganic Chemistry Division; SI units; units of time


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