The goal of this first version of the CRONUS-Earth online exposure age calculator is to codify standard practices for calculating exposure ages from cosmogenic nuclide concentrations in a central and easily accessible location.

We are motivated to develop this exposure-age calculator in the first place by the fact that the number of applications of cosmogenic-nuclide exposure dating, as well as the number of papers published on the subject, has been rapidly growing. Also, these studies are no longer being carried out exclusively by exposure-dating specialists, but by geologists and paleoclimatologists who wish to use exposure ages as part of a broader study. As the technique of exposure dating is still under development, a variety of data-reduction methods, reference nuclide production rates, and production rate scaling schemes exist in the literature. Many of these schemes are at least in part inconsistent with each other, and yield different exposure ages for the same measurements of nuclide concentrations. The effect of this has been that published exposure-dating studies lack a common basis for exposure-age calculations. Even without worrying about the accuracy relative to the true calendar year time scale of any of the calculation methods, this proliferation of inconsistent results makes it difficult for nonspecialists even to compare the results of any two exposure-dating studies. Thus, our goal is to provide a standard method of exposure-age calculation that will allow anyone to easily calculate an exposure age or compare previously published cosmogenic-nuclide measurements in a consistent fashion.

The point of this is that these calculators are intended to give a self-consistent result that reflects standard exposure-dating practices. We can't at this time guarantee that they provide the 'right' answer, that is, that they will always yield the correct calendar age for samples of all locations and ages. There are still many systematic uncertainties in nuclide production rates and scaling factors, and the ones we have chosen to use here may not prove to be the most accurate when more calibration data are available in future. We have chosen production rates and scaling factors that are relatively straightforward to understand and use, are consistent with the calibration measurements that are available, and are as consistent as possible with the majority of common usage in the existing literature. The purpose of the CRONUS-Earth project in general is to improve these production rate scaling schemes in two ways, first by better understanding the physics of cosmogenic-nuclide production, and, second, by collecting a larger calibration data set to better evaluate the various production rates and scaling schemes that have been proposed in the past and will no doubt be proposed in the future. In future, we will have a better basis for choosing the most accurate of the available production rates and scaling factors, and at that time we will issue a new version of these calculators to take account of these improvements.

One critically important part of this effort, that of providing a self-consistent means of comparing exposure ages from different studies, is that it cannot succeed unless everyone who publishes cosmogenic-nuclide exposure ages also reports all the information needed to calculate the ages. In most cases this means the location and elevation of the sample site, the density, thickness and shielding geometry of the sample, any independent information about the erosion rate, and the measured nuclide concentrations and corresponding analytical uncertainties. If these data don't appear in full in a paper or associated data repository, then the exposure ages cannot be recalculated either for comparison with other data sets or to reflect future improvements in the accuracy of production rates or scaling factors, and the study will be effectively useless to future researchers.