This data publication consists of two parts:
(1) the questionnaire for round 1 of the G-Chron proficiency test as provided to the participating laboratories via the on-line data submission portal, and
(2) the complete data set of submitted results.
The results of the survey are published as Scientific Technical Report - Data (STR 21/06, Webb et al., 2020).

The questionnaire is structured into distinct segments. The first “metadata segment” allowed each laboratory to report key parameters describing their analytical technique. This part was structured as five independent tracks based on laboratory technique: isotope dilution thermal ionization mass spectrometry (ID-TIMS), secondary ion mass spectrometry (SIMS), laser ablation inductively coupled sector field mass spectrometry (LA-ICP-MS: SF), laser ablation inductively coupled quadrupole / time-of-flight mass spectrometry (LA-ICP-MS: Quad&ToF), and “other”. When reporting results a given laboratory was to select a single one of these options and then was provided a series of questions relevant to that specific method. The second segment of the questionnaire was provided to all laboratories for them to submit their determined age results. The on-line portal required submission of the determined age and uncertainty for both the 206Pb/238U and 207Pb/206Pb chronometers. Submission of results for the 208Pb/232Th chronometer was optional.

Both the April 2020 report and the subsequent manuscript for publication are based on the table that forms the second part of this document. This contains both the reported age values and information about key aspects of each laboratory’s analytical method. In a small number of cases the input data were corrupted due to an apparent incompatibility between the data portal and the character set used by the submitting laboratory. Where the intent of the laboratory reporting was obvious these have been corrected. For two of the reporting laboratories there a software malfunction resulted in their submissions being classified as “other technique”. These data have now been reassigned to their correct technique categories, but the report has not been accordingly modified. All age values are in Ma. The software specified that uncertainty values should be reported as 1s or 1SE, depending on the nature of the value being addressed, though in a number of instances this instruction appears not to have been applied.