Deep-sea sediments help geological dating

Deep-sea sediments used for geological dating. Credit: Getty Images

In a new study published in the journal Science, Richard Zeebe from the University of Hawai’i at Manoa and Lucas Lourens from Utrecht University, have found that deep-sea sediments can be used to add to the astronomical time scale by approximately eight million years, extending the previous standard of dating back to 50 million years.

The dating of geologic archives has been revolutionised by the development of a so-called astronomical time scale, a calendar of the past providing ages of geologic periods based on astronomy.

For example, cycles in mineralogy or chemistry of geologic archives can be matched to cycles of an astronomical solution, which is done by calculating astronomical parameters from the past and computing the planetary orbits backward in time. The astronomical solution has a built-in clock and so provides an accurate chronology for the geologic record.

However, geologists and astronomers have struggled to extend the astronomical time scale further back than about fifty million years due to a major roadblock: solar system chaos, which makes the system unpredictable beyond a certain point.

This is where the study, titled Solar System chaos and the Paleocene–Eocene boundary age constrained by geology and astronomy, explores the geological archives of our planet, comes in.Zeebe and Lourens analysed sediment data from drill cores in the South Atlantic Ocean across the late Paleocene and early Eocene, from around 58-53 million years ago. The sediment cycles displayed a remarkable expression of one particular Milankovitch parameter, a deviation in Earth’s orbit. The scientists then computed a new astronomical solution (dubbed ZB18a), which showed exceptional agreement with the data from the South Atlantic drill core.

“This was truly stunning,” Zeebe said. “We had this one curve based on data from over 50-million-year-old sediment drilled from the ocean floor and then the other curve entirely based on physics and numerical integration of the solar system. So the two curves were derived entirely independently, yet they looked almost like identical twins.”