If you have ever wished there were more hours in the day, you’re in luck because scientists have discovered that our days are getting longer.
A new study published in the international journal Proceedings of the National Academy of Sciences has reconstructed the deep history of our planet’s relationship to its moon. According to this study, 1.4 billion years ago, a day on Earth lasted just over 18 hours — in part because the moon was closer and changed the way the Earth spun around its axis.
These calculations suggest that the length of our day has increased by approximately 1/75,000 second per year since Precambrian times. This trend is expected to continue for many billions of years to come until the moon finally reaches a stable distance.
“As the moon moves away, the Earth is like a spinning figure skater who slows down as the arms are stretched out,” explains Stephen Meyers, professor of geoscience at the University of Wisconsin–Madison and a co-author of the study.
The research links astronomical theory with geological observations, called astrochronology, to look back on Earth’s geologic past, reconstruct the history of the solar system, and understand ancient climate change as captured in the rock record.
“One of our ambitions was to use astrochronology to develop very ancient geological time scales,” says Meyers in a statement. “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.”
The geoscientists set out to calculate changes in the distance between the Earth and the moon, and variations in Earth’s orbit and rotation axis, along with wobbles and tilts, collectively known as Milankovitch cycles. These variations determine where sunlight is distributed on Earth, so they also influence Earth’s climate rhythms. Scientists have observed this climate rhythm in the rock record, spanning hundreds of millions of years but it has been harder to go back further on the scale of billions of years.
To look at the frequency of the Milankovitch cycles, the scientists looked at copper and aluminium ratios linked to climate change on two stratigraphic rock layers: 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.
This information was used in a model they named TimeOptMCMC, which uses astronomical theory, geologic data, and two different statistical approaches, to reliably assess variations in the direction of the axis of rotation of Earth and the shape of its orbit, both in more recent time and in deep time.
Using the model, Meyers and Malinvern were also able to determine the length of day and the distance between Earth and the moon. According to their calculations, over the past 1.4 billion years, the moon has moved roughly 44,000 km away from Earth to a distance of 384,400 km.