Breakthroughs in geological dating imminent, says ESF
A breakthrough in geological dating, the use of chemical analysis to estimate the age of geological specimens, is very near, say scientists at the European Science Foundation (ESF). The breakthrough, expected to combine current dating methods with new developments, will yield higher accuracy over longer timescales, reaching closer to the Earth's origin. This should not only bring benefits to earth sciences, but also to other fields that rely on accurate dating over geological time, scientists believe. The earth sciences rely on high accuracy to unravel past causes and effects, and to understand the forces driving events from ice ages to mass extinctions. Meanwhile other scientific disciplines, such as evolutionary biology and climate science, depend on accurate timing of geological processes to provide a baseline for their investigations. While significant progress has been made over recent decades, uncertainties remain, inhibiting the investigation of major past events and formative processes. For this reason, the ESF organised a workshop to boost Europe's leading position in geochronology. It identified a need to improve the three main dating methods currently used, and cross-calibrate between them where possible to yield even greater accuracy. 'The main outcome [of the workshop] is that we first aim to work on the improvement of the numerical tools to calibrate the Geological Time Scale,' says Klaudia Kuiper, the scientific convenor of the ESF-sponsored workshop. Although the methods currently employed achieve high-sounding accuracies in the order of 0.5% to 1%, this can equate to an error of several million years over geological timescales. The objective will be to reduce the margin of error to less than 0.1%, equivalent to below an error of 100,000 years over a 100 million year period. The three main tools currently used for dating geological events are argon-argon dating, uranium/lead dating, and astronomical methods. Argon-argon dating measures the level of decay from an isotope of potassium to argon, which occurs predictably over time, but taking into account the proportions of the two different isotopes of argon that form during the process. Uranium/lead dating, one of the oldest and most refined methods, also exploits radioactive decay. However in this case the measurement is based on a correlation between the decay of two isotopes of uranium occurring at different rates, thus boosting the accuracy as a result. Astronomical timing on the other hand is quite different. It exploits long-term cyclical changes in the Earth's orbit and axis. These cause climate changes that can be measured in sediment deposits, providing a dating method that can be correlated with geological events. The methods each have their pros and cons. Astronomical dating is highly accurate, but only over relatively short periods on a geological scale, up to at most 250 million years, which is just 5%of the Earth's current lifespan. Radiometric dating can span the Earth's history back to 4.5 billion years ago, but with less accuracy, and some uncertainties. Currently, astronomical timing is used for events in the last 23 million years, then argon-argon back to 100 million years, and uranium/lead for even older events. Further progress could be made by combining these methods. According to Dr Kuiper, this would usher in a new generation of Geological Time Scale (GTS) measurements that will, in turn, yield fresh insights into critical events during the Earth's history. Dr Kuiper believes these could be just as exciting as some of the insights enabled by the previous generation of dating technologies, such as timing of the great ice ages of the Pleistocene between about 2 million and 11,000 years ago.