Scientists Extend Astronomical Time Scale By 8 Million Years Using Deep-Sea Drill Cores

Scientific drilling ship JOIDES Resolution. The sediment archives obtained during ocean drilling programs give scientists a glimpse into Earth's climatic history and reveal chaos in the Solar System. Inset: Deep-sea sediment cores across the Paleocene-Eoc

Despite all the technology and gadgetry we have developed, we are still a species intimately tied to astronomical time scales. The tick-tock of our watches is based on the twirl of our planet on its axis (a day) and our calendars on the swing of Earth around the Sun (a year). It is easy to forget in the grind of day-to-day life that our Earth orbits a ball of fire in the vast expanse of the universe, its tilt, orbit, and wobble all influential to the creatures within. 

When you expand out – past the city, country, and even our planet – geological time scales reveal a bigger story. Scientists call it the "Astronomical Time Scale": periodic variations in Earth’s tilt and orbit to the Sun that influence our planet’s climate and, therefore, sedimentation sensitive to these influences. This means there is a record of the movement of Earth frozen in sediment spanning tens of millions of years. 

However, researchers get stuck like flies in sticky measuring tape at 50 million years back. At this point, they find “solar system chaos” messing up their ordered calculations and predictions. An uphill battle has been waged to overcome this chaos and extend the astronomical time scale.

Now a team of two researchers has published work in Science that extends the time scale back 8 million years. The duo – Richard Zeebe from the University of Hawai'i at Manoa and Lucas Lourens from Utrecht University – analyzed deep-sea drill cores from the South Atlantic Ocean dated to between 58 and 53 million years ago. The samples revealed information about Earth’s orbital eccentricity.

"This was truly stunning," Zeebe said in a statement. "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." 

Illustration of chaotic trajectories (Poincare section, velocity vs. position) in a simple dynamic system (forced pendulum) from overlapping resonances. Structures of closed curves that appear like rings on a shooting target are regions of stability, whereas densely filled, dotted areas are regions of chaos. Interacting resonances are also suspected to cause chaos in the Solar System, although significantly more complex than the simple system depicted here. Credit: Richard Zeebe

Such an agreement has been seen before – the real breakthrough is in the extra 8 million years they were able to gain from the process. The work provides a new time-stamp for the Paleocene-Eocene boundary (56.01 million years ago) and suggests a dramatic ancient warming event known as the Paleocene-Eocene Thermal Maximum was nudged across a tipping point when Earth reached an eccentricity maximum, essentially a change in Earth’s orbit around the Sun.

This, however, cannot be used to justify today’s climate change, Zeebe warns. "None of this will directly mitigate future warming, so there is no reason to downplay anthropogenic carbon emissions and climate change."

The team also discovered a change in the interaction of Earth’s and Mars’ orbits, which influences their "amplitude modulation" (a beat in music terminology).

"You can hear amplitude modulation when tuning a guitar. When two notes are nearly the same, you essentially hear one frequency, but the amplitude varies slowly – that's a beat," said Zeebe. "The change in beats is a clear expression of chaos, which makes the system fascinating but also more complex. Ironically, the change in beats is also precisely what helps us to identify the solution and extend the astronomical time scale."

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