New Study Reveals that the Moon is Making Days Longer on Earth

For anyone who has ever wished there were more hours in the day, geoscientists have some fascinating news: days on Earth are gradually getting longer. 

This revelation comes from a groundbreaking study that reconstructs the deep history of our planet’s relationship with the moon. 

Astonishingly, 1.4 billion years ago, a day on Earth lasted just over 18 hours. 

This change is partially due to the moon being closer to Earth back then, significantly influencing our planet’s rotation.

Stephen Meyers, a professor of geoscience at the University of Wisconsin–Madison and co-author of the study published in the Proceedings of the National Academy of Sciences, explains the phenomenon using an analogy. 

“As the moon moves away, the Earth is like a spinning figure skater who slows down as they stretch their arms out,” he says. 

This analogy helps illustrate how the increasing distance of the moon from Earth affects our planet’s rotation.

The study utilizes a novel tool, a statistical method known as astrochronology, which links astronomical theory with geological observation. 

This method allows scientists to delve into Earth’s geologic past, reconstruct the history of the solar system, and understand ancient climate changes preserved in rock records. 

The research team’s ambition was to develop geological time scales for very ancient periods, comparable to modern geologic processes.

Earth’s movement through space is influenced by various astronomical bodies that exert forces on it, including the moon and other planets. 

These forces affect the variations in Earth’s rotation and its orbital path around the sun, collectively known as Milankovitch cycles. 

These cycles determine the distribution of sunlight on Earth, thereby influencing our planet’s climate rhythms, which scientists like Meyers have observed in the rock record spanning hundreds of millions of years.

However, reconstructing these cycles over billions of years has been challenging due to the limitations of typical geological dating methods like radioisotope dating, and the complexities introduced by solar system chaos—a theory that small initial variations in the solar system’s moving parts can lead to significant changes over millions of years. 

This theory, proposed by Parisian astronomer Jacques Laskar in 1989, complicates efforts to trace ancient astronomical influences on Earth.

Meyers and his colleagues have made significant strides in understanding these ancient cycles. 

Last year, they cracked the code on the chaotic solar system by studying sediments from a 90 million-year-old rock formation. 

Yet, their efforts to extend this understanding further back in time faced challenges. 

For instance, the current rate of the moon’s recession from Earth suggests that, beyond 1.5 billion years ago, the moon would have been so close to Earth that gravitational interactions could have torn it apart. 

Nevertheless, we know the moon is 4.5 billion years old.

To address these challenges, Meyers collaborated with Alberto Malinverno, a research professor at Columbia University. 

Malinverno proposed combining a statistical method called TimeOpt, which Meyers developed in 2015, with astronomical theory, geological data, and Bayesian inversion, a sophisticated statistical approach. 

This new approach, termed TimeOptMCMC, allows researchers to better handle uncertainties in their study systems.

Testing this approach on the 1.4 billion-year-old Xiamaling Formation from Northern China and a 55 million-year-old record from Walvis Ridge in the southern Atlantic Ocean, the researchers could assess variations in Earth's axis of rotation and orbital shape over deep time with greater reliability. 

They also determined the length of the day and the distance between Earth and the moon at different points in history.

This study complements other recent research that uses rock records and Milankovitch cycles to understand Earth’s history better. 

For example, a team at Lamont-Doherty confirmed the regularity of Earth’s orbital fluctuations over a 405,000-year cycle, while another team in New Zealand, in collaboration with Meyers, studied the effects of Earth's orbital changes on the evolution and extinction cycles of marine organisms called graptoloids over 450 million years.

“The geologic record is an astronomical observatory for the early solar system,” says Meyers. 

“We are looking at its pulsing rhythm, preserved in the rock and the history of life.”

 This research not only provides insight into the dynamic relationship between Earth and the moon but also enhances our understanding of ancient climate patterns and their influence on life’s evolution on our planet.