Breakthrough In Geological Dating Imminent

The developments ushering in a new generation of dating methods were discussed at a recent workshop on geochronological timing organised by the European Science Foundation (ESF).

The earth sciences rely on highly accurate timing to unravel past causes and effects, and understand the forces driving many events from ice ages to mass extinctions. Other scientific disciplines, such as evolutionary biology and climate science, in turn depend on accurate timing of geological processes to provide a baseline for their investigations.

While significant progress has been made over recent decades, great uncertainties remain that are inhibiting investigations of major past events and formative processes in the earth sciences. In the case of the dinosaur extinction, knowledge of how long the process took would help resolve whether this was caused by a sudden asteroid strike or more gradually following a period of intense volcanic activity for example.

There was intense interest therefore in the ESF workshop, which came six years after the launch of an international project in the same field, called EARTHTIME. The workshop was organised to recognise and boost Europe’s leading position in geochronology. It identified the need to improve the three main dating methods currently used, and cross-calibrate between them where possible to yield even greater accuracy, according to Klaudia Kuiper, scientific convenor of the ESF workshop. “The main outcome is that we first aim to work on the improvement of the numerical tools to calibrate the Geological Time Scale,” said Kuiper.

Although these methods currently achieve high-sounding accuracies in the order of 0.5 percent to 1 percent, this can equate to an error of several million years over geological time scales. The objective is to reduce the error to better than 0.1 percent, in other words below an error of 100,000 years over a 100 million year time scale.

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, also taking account of 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, boosting the accuracy as result.

Astronomical timing is quite different, exploiting 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 pros and cons. Astronomical dating is highly accurate, but only over relatively short times on a geological scale, up to at most 250 million years, which is just 5 percent of the earth’s age.  Radiometric dating can span the earth’s whole history back to 4.5 billion years ago, but with less accuracy, and some uncertainties. Currently the astronomical timing is used for events in the last 23 million years, then argon-argon back to 100 million years, and uranium/lead for older events.

Further progress can be made by combining these methods, with astronomical dating already being used to calibrate radiometric timing over the last 10 million years where the former is highly accurate.  According to Kuipers, such progress will 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. Kuipers believed 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. The hope is that the new generation of timing methods will enable older events to be dated accurately.

The workshop Earthtime: The European Contribution - Integration of High-Precision Geochronology and Astronomical Tuning for Calibration of the Cenozoic and Mesozoic Timescales, was held 22-24 April 2007 in Amsterdam, Netherlands, and was convened by Klaudia Kuiper.