Research vessel JOIDES Resolution off the coast of Hawaiʻi. Photo courtesy of UH/International Ocean Discovery Program

In a new study published in the journal Science, a University of Hawaiʻi at Mānoa researcher and a colleague overcome a roadblock that had hampered astronomers and geologists to accurately date geologic archives older than 50 million years using a “calendar” of the past that provides ages of geologic periods based on astronomy, called the astronomical time scale, according to a UH news report.

Richard Zeebe from UH Mānoa and Lucas Lourens from Utrecht University were able to extend the astronomical time scale by about 8 million years. Further application of their new method holds promises to reach further back in time still, one step and geologic record at a time.

The team used geologic records from deep-sea drill cores to constrain the astronomical solution (calculated astronomical parameters in the past from 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.

Geologists and astronomers had struggled to extend the astronomical time scale further back than about 50 million years due to solar system chaos, which makes the system unpredictable beyond that point.

Zeebe and Lourens analyzed sediment data from drill cores in the South Atlantic Ocean across the late Paleocene and early Eocene, ca. 58-53 million years ago. Zeebe and Lourens 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.”

Zeebe and Lourens are not the first to discover such agreement—the breakthrough is that their time window is older than 50 million years, where astronomical solutions disagree. They tested 18 different published solutions, but ZB18a gave the best match with the data.

One implication of their work is that researchers can reach much further back in time with more accuracy. Using their new chronology, they provided a new age for the Paleocene-Eocene boundary at 56.01 million years ago, with a small margin of error of 0.1 percent.

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