In the 1950's much of the theoretical grounds for the technique had been laid out, including estimates of how the cosmic ray flux varied over Earth. Although it was realized early on that the products of the interaction between cosmic rays and minerals could be used as a geochronometer, the community was limited by the inability to measure low isotope abundances.
In the 1980's, significant improvements in mass spectrometry (gas MS and accelerator MS) permitted the precise measurement of low abundances (i.e. only a million atoms per gram of rock) of cosmogenic nuclides. The theory and measurement of cosmogenic nuclides were tied together and numerous Earth Sciences applications were devised.
The concept of the CRONUS-Earth project began in March, 2002 during an international meeting at Lamont Doherty Oceanographic Observatory organized by J-rg Sch"fer. Geochemists and physicists who are interested in various influences of the production rates and measurement of cosmogenic nuclide in minerals on Earth reviewed ongoing projects aimed at improving applications of cosmogenic nuclides in Earth Sciences. Previously recognized and newly identified sources of error were discussed and strategies of reducing some of those uncertainties were proposed. When the systematic and random errors were combined, the overall uncertainty of most applications of cosmogenic nuclides is the limiting control on the types of questions that the method can address. (i.e. we are no longer limited by the isotope chemistry or analysis).
In July, 2002, a group representing US participants in the CRONUS-Earth project met with pertinent program managers and the director of the Earth Sciences Division of the National Science Foundation. During the meeting, details on the successes of applications of the cosmogenic nuclide methods were described, the status of improvements in uncertainties were outlined, and the objectives and role of an international project directed toward improving the methods were presented. The participants reviewed approximately how much NSF funding was already spent on the method, and how the amount of funding, numbers of projects, and numbers of publications have been increasing exponentially since the 1980's. This demonstrated the urgency in improving the methods.
Later in 2002, four international meetings had been convened at meetings where geochronologists, geochemists, accelerator mass spectrometrists, geomorphologists, and geophysicists were able to discuss concerns of the cosmogenic method, and the potential role of a collaborative, international pooling of ideas, expertise, facilities, and funding.
At the first two meetings, the need and role of a CRONUS-Earth project was discussed. The second two meetings and future meetings will be focused on presenting results and discussing strategies for improving various cosmogenic nuclide methods.