This article was originally published dialogue. (Opens in a new tab) Post contributed this article to Space.com Expert Voices: Editorials and Perspectives.
Joshua Davis (Opens in a new tab)Professor of Earth and Atmospheric Sciences, University of Quebec at Montreal (UQAM)
Margaret Lantin (Opens in a new tab)Postdoctoral Researcher, Department of Earth Sciences, University of Wisconsin-Madison
Looking at the moon in the night sky, you would never imagine that it is slowly moving away from the earth. But we know the opposite. In 1969, NASA’s Apollo missions installed reflective panels on the lunar surface. This showed that the Moon is currently moving away from Earth by 3.8 cm every year (Opens in a new tab).
If we take the Moon’s current stagnation rate and project it over time, we’d end up with a collision between the Earth and the Moon about 1.5 billion years ago. (Opens in a new tab). However, the moon formed about 4.5 billion years ago (Opens in a new tab)Which means that the current recession rate is poor evidence of the past.
With our research colleagues from Utrecht University (Opens in a new tab) and the University of Geneva (Opens in a new tab)We have 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 by studying the moon itself, but by studying the moon and reading the signs in the layers of ancient rocks on Earth (Opens in a new tab).
Related: How is the moon formed?
Read between classes
In the beautiful Karigeni National Park (Opens in a new tab) In Western Australia, some gorges are cut by 2.5 billion-year-old rhythmic layered sediments. These deposits are striped iron formations, consisting of layers of minerals rich in iron and silica (Opens in a new tab) They were deposited on a large scale on the ocean floor and are now found in the oldest parts of the Earth’s crust.
Cliff Shows at Joffrey Falls (Opens in a new tab) Show how the reddish-brown iron formation layers just under a meter thick alternate, at regular intervals, with darker and thinner horizons.
Dark spacers consist of a softer rock type that is more susceptible to erosion. Closer examination of the bumps reveals a more regular and smaller contrast. The rocky surfaces, polished by seasonal river waters flowing through the valley, reveal a pattern of alternating layers of white, red, and bluish-gray.
In 1972, Australian geologist AF Trendall raised the question of the origin of various scales of periodic and recurring patterns (Opens in a new tab) Visible in these ancient rock layers. He noted that the patterns can be linked to past changes in climate caused by the so-called “Milankovitch cycles”.
Periodic climate changes
Milankovitch cycles describe how a small periodic change in the shape of the Earth’s orbit and the direction of its axis affects the distribution of sunlight the Earth receives. (Opens in a new tab) 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.
The main examples of the effect of the Milankovitch climate effect in the past are the occurrence of extreme cold (Opens in a new tab) Where are the hot periods? (Opens in a new tab)As good as wet (Opens in a new tab) or drier regional climatic conditions.
These climatic changes have led to a significant change in conditions on the Earth’s surface, such as the size of lakes (Opens in a new tab). They explain the periodic greening of the Saharan desert (Opens in a new tab) And low levels of oxygen in the deep oceans (Opens in a new tab). Milankovitch cycles also influenced the migration and evolution of plants and animals (Opens in a new tab) Including special species (Opens in a new tab).
The signatures of these changes can be read by periodic changes in sedimentary rocks (Opens in a new tab).
recorded oscillations
The distance between the Earth and the Moon is directly related to the frequency of one of the Milankovitch cycles – the cycle of climate movement (Opens in a new tab). This cycle arises from the anticipatory movement (oscillation) or change in the direction of the Earth’s rotation axis over time. This cycle is currently about 21,000 years long, 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 ancient sediments, then find a signal of Earth’s oscillation and determine the time period for it, we can estimate the distance between Earth and the Moon at the time the sediments settled.
Our previous research showed that Milankovitch cycles could also be conserved in the ancient iron-domain formation in South Africa (Opens in a new tab)Thus supporting Trendall’s theory.
The banded iron formations in Australia were probably deposited in the same ocean (Opens in a new tab) Like the rocks of South Africa, about 2.5 billion years ago. However, the periodic variations of Australian rocks are better exposed, allowing us to study the variations at much higher resolution.
Our analysis of Australian iron bands formation showed that the rocks contain multiple scales of periodic variations that repeat at ~4 and 33 inch (10 and 85 cm intervals). By combining these thicknesses with the rate of sediment deposition, we find that these periodic variations occur 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 pre-emptive signal to calculate the distance between the Earth and the Moon 2.46 billion years ago (Opens in a new tab).
We found that the Moon was close to Earth by about 37,280 miles (60,000 km) (this distance is about 1.5 times the circumference of the Earth). This would make the length of the day much shorter than it is now, at around 5 pm instead of the current 24 hours.
Understand the dynamics of the solar system
Astronomical research has provided models for the formation of our solar system (Opens in a new tab)And notes for the current circumstances (Opens in a new tab).
Our study and some research by others (Opens in a new tab) It is one of the only ways to get real data on the evolution of our solar system, and future models of the Earth-Moon system will be necessary (Opens in a new tab).
It is really amazing that the dynamics of the previous solar system can be determined by small differences in ancient sedimentary rocks. However, a significant data point does not give us a complete understanding of the evolution of the Earth-Moon system.
We now need more reliable data and new modeling methods to track the moon’s evolution over time. And our research team has already begun searching for the next set of rocks that could help us discover more clues to the history of the solar system.
This article has been republished from dialogue (Opens in a new tab) Under Creative Commons License. Read it original article (Opens in a new tab).
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