Moon has been slowly slipping away from Earth over last 2.5 billion years, study confirms

Length of a day during this period was much shorter at roughly 17 hours, scientists say

The Earth-Moon distance was about 60,000 km closer about 2.5 billion years ago, according to a new study which confirms that the Moon has been slowly drifting away during this period.

About 2.46 billion years ago the distance between our planet and the Moon was around 321,800 km compared to the current 384,400 km, and day length was around 16.9 hours as opposed to 24 hours, the study, published recently in the journal PNAS, noted.

Researchers, including those from Utrecht University in The Netherlands, say these findings extend our understanding of early Earth-Moon dynamics by over a billion years.

In the study, scientists analysed ancient layers of rocks in the Karijini National Park in western Australia which has gorges cutting through 2.5 billion-year-old sediments.

The sediments, they say, are made of distinct sections of iron and silica-rich minerals, containing alternating white, reddish and blueish-gray layers, that were once widely deposited on the ocean floor.

These rocks now make up the oldest parts of the Earth’s crust, scientists say.

Previous studies have suggested that these distinct alternating patterns are associated with past variations in the planet’s climate induced by what’s called the “Milankovitch cycles.”

These are climate cycles linked to the orientation of Earth’s spin axis and the elliptical nature of its orbit – features that determine the distribution of sunlight received by Earth over long time periods.

Dominant periods of the Milankovitch cycles currently change every 400,000 years, 100,000 years, 41,000 years, and 21,000 years, and scientists say these changes can exert a strong control on the planet’s climate over long durations, including years of extreme cold or warmth, or wetter or dryer conditions.

One of the Milankovitch cycles called the climatic precession cycle emerges from Earth’s wobble as it spins around its axis over time, and this cycle currently has a duration of about 21,000 years.

But researchers say this period would have been shorter in the past when the Moon was closer to the Earth.

Analysis of the ancient mineral layer formations in Australia also points to an 11,000-year cycle about 2.5 billion years ago linked to the climatic precession cycle – a much shorter period than the current frequency of 21,000 years.

Based on these findings, researchers say Moon was indeed closer to our planet, confirming that it is slowly drifting away.

“We found that the moon was around 60,000 kilometers closer to the Earth then. This would make the length of a day much shorter than it is now, at roughly 17 hours rather than the current 24 hours,” scientists write in The Conversation.

Researchers believe the findings provide a new reference point for modeling the evolution of the Earth-Moon system.