Our moon has been slowly drifting away from Earth over the past 2.5 billion years

[Admin]

Looking up at the moon in the night sky, you would never imagine that it is slowly moving away from Earth. But we know otherwise.

Our moon has been slowly drifting away from Earth over the past 2.5 billion years : Read more

 

[rod]

Extrapolating the tidal dissipation rate back, the Moon and Earth are within the Roche limit about 1.5 billion years ago or near 3 earth radii separation. Other reports show the strata do not come so neatly in layers that unravel the story of the receding Moon so cleanly.

Ref paper - Milankovitch cycles in banded iron formations constrain the Earth–Moon system 2.46 billion years ago, https://www.pnas.org/doi/abs/10.1073/pnas.2117146119, 26-Sep-2022. "Significance Milankovitch cycles recorded in 2.46-billion-year-old sediments indicate that Earth’s precession cycle had a significantly higher frequency than present, signaling shorter daylengths and Earth–Moon distance..."

My observation. Using the data provided here, Earth in the Precambrian model 2.46 Gyr had a LOD 16.9 hours and the Moon orbited about 50.45 earth radii distance compared to the present mean near 60.27 earth radii distance. Using a circular orbit for the Moon, the lunar month or period ~ 20.9 days. Earth spin at its equator with LOD 16.9 h = 0.6587 km/s. Other reports, Slowdown of Earth's spin caused an oxygen surge, https://forums.space.com/threads/slowdown-of-earths-spin-caused-an-oxygen-surge.40239/, 21 h LOD 2 Gyr.

Thank the moon for Earth's lengthening day, https://www.sciencedaily.com/releases/2018/06/180604151200.htm, "A new study that reconstructs the deep history of our planet's relationship to the moon shows that 1.4 billion years ago, a day on Earth lasted just over 18 hours"

My question, are these Earth-Moon system models using Precambrian strata consistent and reliably trace the past history of the orbit of the Earth-Moon system back perhaps 2.5 Gyr? Notice we have an 18 h LOD 1.4 Gyr, 21 h LOD 2 Gyr, and the phys.org report 16.9 h LOD 2.46 Gyr. When you examine the giant impact model(s) for the origin of the Moon, system spin rates and distances are very different, a number show the Moon about 3-7 earth radii when it forms with the proto-earth spinning with a 2-5 hour LOD.

 

[Unclear Engineer]

Regarding the current rate of recession, I wonder how sea level plays into that number.

The more mass there is to get spun out ahead of the moon's tidal pull on the ocean, the faster the Earth's rotational energy gets transferred to the Moon's orbital energy, and the faster the Moon moves away and the quicker Earth's day lengthens.

So, I am not surprised that the recession rate is higher now than it would be during an ice age, when a lot of the movable ocean water mass was literally frozen in-place.

But, most of Earth's history over the last 2.5 billion years was not ice ages. So, I wonder how the recession rate is as high as it is, today, without being high enough in the past to get the Moon closer to the Earth than it realistically could have been billions of years ago.

 

[rod]

"But, most of Earth's history over the last 2.5 billion years was not ice ages. So, I wonder how the recession rate is as high as it is, today, without being high enough in the past to get the Moon closer to the Earth than it realistically could have been billions of years ago."

My thinking, the only solid method of determining changes in the Moon's distance and Earth rotation changes in the past, comes from comparing ancient solar eclipse records with current measurements. Some Assyrian and Babylonian accounts go back some 3,000 years ago, perhaps 3500 years ago. A Chinese report may date back near 1900 BC or 3800-3900 years ago. Beyond that, there is no direct measurement supporting such lunar changes. This applies to the giant impact model to explain the origin of the Moon today too. We do not see a Moon more than 5-degrees angular size and moving around the Earth in a one-day period.