Where this has been done a note explains the correction. In this way, we hope to correct for changes in standards, different techniques, different mass spectrometers, and hopefully other systematic errors. A ascii text version of the data used to make this figure is also available. Be aware that the data is very sparse in many areas, and gridded data sets can offer the illusion of completeness. All references have been checked and if necessary, corrected.
All references are now in the reference list.
Some institutions and individual researches were kind enough to let us have unpublished data, for which we are thankful. Gilles Delaygue, Mike Meredith, Duane Thresher, Martin Wadley have also been especially helpful. Samar Khatiwala, Lee Cooper, Peter Strain and Peter Schlosser were kind enough to give us there own collected data sets. Finally, we thank the researchers who worked hard to collect this data - often in very difficult circumstances. References for all the data included are also available.