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Pure Appl. Chem., 2011, Vol. 83, No. 5, pp. 1159-1162

Published online 2011-04-08

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

Norman E. Holden1,2, Mauro L. Bonardi1,3, Paul De Bièvre4,1, Paul R. Renne5,6,7 and Igor M. Villa8,7,9*

1 International Union of Pure and Applied Chemistry
2 National Nuclear Data Center, Brookhaven National Laboratory, Upton, NY 11973, USA
3 LASA, Università degli Studi di Milano and INFN, I-20090 Segrate, Italy
4 Consultant on Metrology in Chemistry, Duineneind 9, B-2460 Kasterlee, Belgium
5 Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94720, USA
6 Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA
7 International Union of Geological Sciences
8 Institut für Geologie, Universität Bern, CH-3012 Bern, Switzerland
9 Università di Milano Bicocca, I-20126 Milano, Italy

Abstract: 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.