Paleontology news: Researchers recalculate age of Solar System

Lead-lead (Pb-Pb) dating is among the most widely used radiometric dating techniques to determine the age of really old things, such as the age of the Earth or the Solar System. However, recent advances in instrumentation now allow scientists to make more precise measurements that promise to revolutionize the way the ages of some samples are calculated with this technique.

Radiometric dating can be used to determine the age of a wide range of natural and human-made materials. The comparison between the observed abundance of a naturally occurring radioactive isotope, such as uranium (U), and its decay products can be used to determine the age of a material, using known decay rates. The Pb-Pb dating technique has been used for decades under the assumption that the ratio of the 238U and 235U isotopes, both of which decay to different isotopes of Pb, is constant in the Solar System. This assumed value is built into the Pb-Pb age equation.

According to research published online in the Dec. 31 issue of Science Express and in the Jan. 22 issue of Science magazine by Greg Brennecka, a graduate student in the School of Earth and Space Exploration (SESE) at Arizona State University (ASU), the 238U/235U ratio can no longer be considered a constant in meteoritic material. Any deviation from this assumed value causes miscalculation in the determined Pb-Pb age of a sample, meaning that the age of the Solar System could be miscalculated by as much as several million years. Although this is a small fraction of the 4.57 billion year age of the Solar System, it is significant since some of the most important events that shaped the Solar System occurred within the first 10 million years of its formation.

Brennecka and colleagues at ASU and at the University of Frankfurt, Germany, measured the 238U/235U ratio in the earliest solids in the Solar System, calcium-aluminum-rich inclusions (CAIs). CAIs were the first solids to condense from the cooling protoplanetary disk during the birth of the Solar System. The absolute ages of the CAIs, determined through Pb-Pb dating, are generally considered to date the origin of the Solar System. The high-precision data they obtained from CAIs of the Allende meteorite showed that the 238U/235U ratio is not the same in all CAIs. ...

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