Our Moon has been slowly moving away from Earth for the past 2.5 billion years

Our Moon has been slowly moving away from Earth for the past 2.5 billion years

The Moon currently moves 3.8 cm from Earth every year. credit: shutterstock

Looking at the moon in the night sky, you would never imagine 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 have shown that the moon is It currently moves 3.8 cm away from Earth every year.

If we take the moonThe current stagnation rate and dropping in time, we end up with A collision between the Earth and the Moon about 1.5 billion years ago. However, the moon was formed About 4.5 billion years agowhich means that the current recession rate is poor evidence of the past.

Together with our fellow researchers from Utrecht University and the University of GenevaWe’ve used a range of techniques to try to get information about the distant past of our solar system.

We recently discovered the perfect place to reveal the long-term history of our waning moon. And it is not from studying the moon itself, but from reading the signals in ancient rock layers on Earth. Our latest studies appear in Proceedings of the National Academy of Sciences.

Reading between classes

in the beautiful Karigeni National Park In Western Australia, some gorges penetrate 2.5 billion-year-old rhythmic layered sediments. These deposits are striped iron formations, consisting of distinct formations Layers of iron and minerals rich in silica Once large-scale deposited on the bottom of the ocean It is now found in the oldest parts of the Earth’s crust.

Cliff’s Showcase Geoffrey Falls Show how layers of reddish-brown iron formation slightly less than a meter thick alternate in regular periodswith thinner and darker horizons.

Our Moon has been slowly moving away from Earth for the past 2.5 billion years

Joffrey Gorge in Carigeni National Park in Western Australia, showing a regular alternation between reddish-brown, hard rock and softer, clay-rich rock (indicated by arrows) with an average thickness of 85 cm. These changes are attributed to past climatic variations caused by differences in the eccentricity of the Earth’s orbit. Credit: Frits Helgen, author provided

Dark spacers are made of a softer type of rock that is more susceptible to erosion. A closer look at the bumps reveals a smaller, regular contrast. The rocky surfaces, polished by the waters of the seasonal rivers running through the valley, reveal a pattern of alternating white, red, and bluish-gray layers.

In 1972, Australian geologist AF Trendall raised the question about The origin of the various scales of the periodic and recurring patterns visible in these ancient rock layers. He suggested that the patterns may be related to past changes in climate caused by the so-called “Milankovitch cycles.”

Periodic climate changes

Milankovitch courses Describe how small, periodic changes in the shape of the Earth’s orbit and the direction of its axis affect the distribution of sunlight the Earth receives over the years.

Currently, the dominant Milankovitch cycles change every 400,000 years, 100,000 years, 41,000 years and 21,000 years. These differences exert strong control over our climate over long periods of time.

The main examples of the effect of the Milankovitch climate effect in the past are the occurrence of Pretty cold or warm periodsBeside moist Or dry regional climatic conditions.

These climatic changes have significantly altered the conditions on the Earth’s surface, such as The size of the lakes. They are the interpretation of Periodic greening of the Saharan desert And the Low levels of oxygen in the deep ocean. Milankovitch cycles also influenced Migration and evolution of plants and animals including special species.

The signatures of these changes can be read Periodic changes in sedimentary rocks.

Our Moon has been slowly moving away from Earth for the past 2.5 billion years

Rhythmically alternating layers of white, reddish and/or bluish-gray rocks with an average thickness of about 10 cm (see arrows). The changes, interpreted as a signal of the Earth’s motion cycle, help us estimate the distance between the Earth and the Moon 2.46 billion years ago. Credit: Frits Helgen

recorded oscillation

The distance between the Earth and the Moon is directly related to the frequency of one of the Milankovitch cycles –climate cycle cycle. this is Course It arises from the preliminary movement (vibration) or the change in the direction of the Earth’s rotation axis over time. This cycle is currently 21,000 years long, but this period was shorter in the past when the Moon was closer to the Earth.

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

Show our previous search That Milankovitch cycles can be preserved in the formation of ancient iron-bands in South Africathus supporting Trendall’s theory.

banding iron formations Maybe in Australia deposited in the same ocean Like the rocks of South Africa, about 2.5 billion years ago. However, the periodic variations in Australian rocks are better exposed, allowing us to study the variations at much higher resolution.

Our analysis of the Australian Banded Iron Formation showed that the rocks contain multiple scales of periodic variations that repeat approximately at 10 and 85 cm intervals. When combining these thicknesses with the rate at which the sediments were deposited, we find that these periodic changes occurred approximately every 11,000 years and 100,000 years.

Therefore, our analysis suggested that the 11,000 cycle observed in the rocks is likely related to a climatic introduction cycle, having a much shorter period than the current 21,000 years. Then we used this anticipatory reference to Calculate the distance between the Earth and the Moon 2.46 billion years ago.

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

Our Moon has been slowly moving away from Earth for the past 2.5 billion years

We found that the Moon was closer to Earth by about 60,000 km 2.46 billion years ago. credit: shutterstock

Understanding the dynamics of the solar system

Research in astronomy has provided models for Shaping our solar systemAnd the Notes for the current conditions.

Our study and Some research by others It is one of the only ways to get real data on the evolution of our solar system, and it will be necessary Future models of the Earth-Moon system.

It is really amazing that the dynamics of the past solar system can be determined from small differences in the ancient sedimentary rocks. However, there is an important data point that does not give us a complete understanding of the evolution of the Earth-Moon system.

We now need other reliable data and new modeling methods to track the moon’s evolution through time. And our research team has already started looking for the next set of rocks that could help us discover more clues about the history of the solar system.

Hard archives record variations in Earth’s orbit

more information:
Margriet L. Lantink et al, Milankovitch cycles in iron-banded formations constraining the Earth-Moon system 2.46 billion years ago, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2117146119

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