Secrets of the Moon’s slow escape revealed in the Earth’s Crust

(ORDO NEWS) — Looking at the Moon in the night sky, you would never think that it is slowly moving away from the Earth.

But we know otherwise. In 1969, NASA’s Apollo missions installed reflective panels on the Moon. They showed that the Moon is currently moving away from the Earth by 3.8 centimeters every year.

If we take the Moon’s current receding rate and project it back in time, we get a collision between the Earth and the Moon about 1.5 billion years ago.

However, the Moon formed about 4.5 billion years ago, which means that the current rate of recession is a poor benchmark for the past.

Together with our fellow researchers from the University of Utrecht and the University of Geneva, we are using a combination of methods to try to get information about the distant past of our solar system.

We recently discovered the perfect location to reveal the long history of our receding Moon. And this is not from studying the moon itself, but from reading signals in ancient rock layers on Earth.

Reading Between Layers

In Western Australia’s beautiful Karijini National Park, some gorges cut through rhythmically layered deposits dating back 2.5 billion years.

These deposits are banded formations of iron, composed of characteristic layers of minerals rich in iron and silica, which were once widely deposited on the ocean floor and are now found in the most ancient parts of the earth’s crust.

Rock outcrops at Joffre Falls show how layers of reddish-brown iron formation just under a meter thick alternate at regular intervals with darker, thinner horizons.

The darker intervals are composed of softer rocks more prone to erosion. A closer examination of the outcrops reveals the presence of an additional regular variation on a smaller scale.

Rock surfaces, polished by seasonal river water flowing through the gorge, reveal a pattern of alternating white, reddish and bluish-gray layers.

In 1972, the Australian geologist A.F. Trendall raised the question of the origin of the various scales of cyclic repeating patterns seen in these ancient rock layers.

He suggested that the patterns could be related to past climate changes caused by so-called “Milankovitch cycles”.

Cyclical climate change

Milankovitch cycles describe how small, periodic changes in the shape of the Earth’s orbit and the orientation of its axis affect the distribution of sunlight received by the Earth over several years.

Now the dominant Milankovitch cycles change every 400,000 years, 100,000 years, 41,000 years. , and 21,000 years. These changes have a strong impact on our climate over long periods of time.

Key examples of past climate impacts of Milankovitch are extreme cold or warm periods, and wetter or drier regional climates. climatic conditions.

These climatic changes have significantly changed conditions on the Earth’s surface, such as the size of lakes.

They explain the periodic greening of the Sahara desert and the low oxygen levels in the deep ocean.

The Milankovitch cycles also influenced the migration and evolution of flora and fauna, including our own species.

And signs of these changes can be read in the cyclical changes in sedimentary rocks.

Registered fluctuations

The distance between the Earth and the Moon is directly related to the frequency of one of the Milankovitch cycles – the climatic precession cycle.

This cycle occurs due to precessional motion (wobble) or a change in the orientation of the Earth’s axis of rotation over time.

This cycle currently has a duration of ~21,000 years, but this period would have been shorter in the past when the Moon was closer to the Earth.

This means that if we can first find Milankovitch cycles in old sediments and then find the Earth wobble signal and set its period, we can estimate the distance between the Earth and the Moon at the time the sediments were deposited.

Our previous study has shown that Milankovitch cycles may persist into an ancient banded iron formation in South Africa, supporting Trendall’s theory.

The banded iron formations in Australia probably formed in the same ocean as the South African rocks about 2.5 billion years ago. However, the cyclic variation in Australian breeds is better defined, allowing us to study variation at a much higher resolution.

Our analysis of the Australian Banded Iron Formation has shown that the rocks contain several scales of cyclic variation that roughly repeat at intervals of 10 and 85 centimeters

By correlating these thicknesses with the deposition rate, we found that these cyclical changes occurred approximately every 11,000 years and 100,000 years.

Therefore, our analysis showed that the 11,000 cycles observed in the rocks are likely associated with a climatic precession cycle that has a much shorter period than the current 21,000 years.

We then used this precession signal to calculate the distance between the Earth and the Moon 2.46 billion years ago.

We found that the Moon was then about 60,000 kilometers closer to the Earth (this distance is about 1.5 times greater than the circumference of the Earth). This would make the day much shorter than it is now, by about 17 hours instead of the current 24 hours.

Understanding the Dynamics of the Solar System

Astronomical research has provided models for the formation of our solar system and observations of current conditions.

Our study and some others’ studies represent one of the few methods of obtaining real data on the evolution of our solar system and will be critical to future models of the Earth-Moon system.

Surprisingly, the past dynamics of the solar system can be determined from small variations in ancient sedimentary rocks.

However, one important data point does not give us a complete understanding of the evolution of the Earth-Moon system.

Now we need other reliable data and new modeling approaches to follow the evolution of the Moon over time.

And our research team is already on the hunt for the next group of rocks that could help us learn more about the history of the solar system.


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