Intercalibration
Sidney Hemming reports on inter-laboratory and inter-method comparison of the Fire Clay tonstein. See her report here.

Renne et al. (2010) presents a statistical optimization approach allowing constraints from 40K activity data, K–Ar isotopic data, and pairs of 238206Pb and 40Ar/39Ar data for rigorously selected rocks to be used as inputs for estimating the partial decay constants (ke and kb) of 40K and the 40Ar*/40K ratio (jFCs) of the widely used Fish Canyon sanidine (FCs) standard and suggest a value of 28.305 ± 0.036. Following the subsequent discussion by Schwartz et al. (2011) and Renne et al. (2011), a new value is suggested, 28.294± 0.036.

Separates of zircon and feldspar for analysis are now available. See our newsletter: Availability of zircon and feldspar separates from “Proof of Concept” samples and continued cross-calibration between the U-Pb and Ar-Ar systems. Read the pdf here.

A new paper by Klaudia Kuiper and co-workers published in Science Magazine on synchronizing rock clocks of earth is receiving a lot of attention. The paper is an attempt to use astronomically forced cycles from the Miocene to recalibrate the age of the most popular Ar-Ar geochronology standard, the Fish Canyon Tuff sanidine, and then recalibrate the 2006 Timescale. The paper implies that the long-recognized discrepancy between Ar-Ar dates and U-Pb dates may be eliminated by the use of a new age for the Fish Canyon sanidine. This is a bold new approach that should be critically reviewed by the EARTHTIME community. Please visit the Astronomical Tuning page for relevant links.

For the perspective of the Berkeley Geochronology Center on the importance of Ar-Ar dating and intercalibration issues in light of Kuiper et al go here.

You might also interested in the Correspondence by Pälike and Hilgen entitled, Rock clock synchronization.


EARTHTIME is supported by the National Science Foundation.