So since the moon is moving away from the Earth, it’s not a coincidence that the moon appears the same size as the sun, the coincidence is that we happen to live during this time to see such a thing.
TL;DR
Geoscientists have discovered that Earth’s days are gradually lengthening due to the moon’s slow retreat from Earth. About 1.4 billion years ago, a day was just over 18 hours long. The study used astrochronology, a tool combining astronomical theory and geological data, to trace Earth’s ancient interactions with the moon. As the moon moves away, Earth’s rotation slows, similar to a spinning figure skater extending their arms. This gradual change also affects Earth’s climatic rhythms through Milankovitch cycles, influencing Earth’s rotation, wobble, and orbit, and leaving clues in rock formations.
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For those who have ever wished for longer days, geoscientists have some promising news: Earth’s days are gradually lengthening.
A study reconstructing the ancient history of Earth’s interaction with the moon shows that about 1.4 billion years ago, a day on Earth was just over 18 hours long. This shorter day length was partly due to the moon being closer, which influenced how Earth rotated on its axis.
“As the moon moves away, the Earth is like a spinning figure skater who slows down as they stretch their arms out,” explains Stephen Meyers, a geoscience professor at the University of Wisconsin–Madison and co-author of the study published in the Proceedings of the National Academy of Sciences.
The study introduces a tool, a statistical method that merges astronomical theory with geological observation, known as astrochronology. This tool allows scientists to look back into Earth’s geological past, reconstruct the history of the solar system, and understand ancient climate changes as recorded in rocks. “One of our ambitions was to use astrochronology to tell time in the most distant past, to develop very ancient geological time scales,” Meyers says. “We want to be able to study rocks that are billions of years old in a way that is comparable to how we study modern geologic processes.”
Earth’s motion in space is influenced by other celestial bodies exerting forces on it, such as planets and the moon. This affects variations in Earth’s rotation, its wobble on its axis, and its orbit around the sun.
These variations, collectively known as Milankovitch cycles, influence the distribution of sunlight on Earth, thereby controlling Earth’s climatic rhythms. Scientists like Meyers have traced these climate patterns in the rock record spanning hundreds of millions of years.
However, tracing these cycles back billions of years is challenging due to the limitations of traditional geological methods, like radioisotope dating, which lack the precision needed for identifying such cycles. Additionally, uncertainties about the moon’s history and the concept of solar system chaos, a theory proposed by astronomer Jacques Laskar in 1989, complicate matters further.
The solar system’s complexity, with its many moving parts including other planets, can cause small initial changes that evolve into significant effects millions of years later—a phenomenon known as solar system chaos. Tracing these effects in reverse is as challenging as tracking the butterfly effect backward.
“As the moon moves away, the Earth is like a spinning figure skater who slows down as they stretch their arms out.” – Stephen Meyers
Last year, Meyers and his team made progress in decoding the chaotic solar system by studying sediments from a 90 million-year-old rock formation that captured Earth’s climate cycles. However, the further they delve into the rock record, the less reliable the findings become.
For example, the moon is currently receding from Earth at a rate of 3.82 centimeters per year. Using this rate to calculate backwards, scientists found that “beyond about 1.5 billion years ago, the moon would have been close enough that its gravitational interactions with the Earth would have ripped the moon apart,” Meyers explains. Yet, the moon is known to be 4.5 billion years old.
Alberto Malinverno, a Lamont Research Professor at Columbia, was in the audience that day. “I was sitting there when I said to myself, ‘I think I know how to do it! Let’s get together!’” says Malinverno, who co-authored the study. “It was exciting because, in a way, you dream of this all the time; I was a solution looking for a problem.”
Meyers sought a more accurate way to understand the past movements of our planetary neighbors and their effects on Earth and its Milankovitch cycles. He discussed this challenge during a talk at Columbia University’s Lamont-Doherty Earth Observatory while on sabbatical in 2016.
Meyers and Malinverno collaborated to combine Meyers’ 2015 statistical method, called TimeOpt, which addresses uncertainties over time, with astronomical theory, geological data, and a sophisticated statistical approach known as Bayesian inversion. This combination allowed the researchers to better manage uncertainties in the study system.
They tested their method, named TimeOptMCMC, on two sets of stratigraphic rock layers: the 1.4 billion-year-old Xiamaling Formation in Northern China and a 55 million-year-old record from Walvis Ridge in the southern Atlantic Ocean.
This approach enabled them to accurately analyze variations in Earth’s axis of rotation and orbital shape as recorded in rock layers, both in recent times and deep geological history, while also addressing uncertainties. They were also able to determine the length of the day and the distance between Earth and the moon.
“In the future, we want to expand the work into different intervals of geologic time,” says Malinverno.
“It was exciting because, in a way, you dream of this all the time; I was a solution looking for a problem.” – Alberto Malinverno
The study builds on two other recent studies that utilize rock records and Milankovitch cycles to gain a better understanding of Earth’s history and behavior.
One research team at Lamont-Doherty confirmed the regularity of Earth’s orbital fluctuations from nearly circular to more elliptical on a 405,000-year cycle using rock formations in Arizona. Another team in New Zealand, working with Meyers, examined how changes in Earth’s orbit and axial rotation have influenced the evolution and extinction cycles of marine organisms known as graptoloids over the past 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.”
The study was funded by the National Science Foundation (EAR-1151438).
