This article was originally published on Conversation. (Opens in a new tab) Post contributed this article to Space.com Expert Voices: Editorial and Insights.
Joshua Davis (Opens in a new tab)Professor of Earth and Atmospheric Sciences, University of Quebec at Montreal (UQAM)
Margaret Lantinck (Opens in a new tab)Postdoctoral Research Associate, 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 otherwise. In 1969, NASA’s Apollo missions installed reflective panels on the Moon. This showed that the Moon is currently moving 3.8 cm from Earth every year (Opens in a new tab).
If we take the moon’s current stagnation rate and back in 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 fellow researchers from Utrecht University (Opens in a new tab) and the University of Geneva (Opens in a new tab)We’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 signs in ancient rock layers on Earth (Opens in a new tab).
Related: How was the moon formed?
Reading between classes
In the beautiful Karigeni National Park (Opens in a new tab) In Western Australia, some gorges penetrate 2.5 billion-year-old rhythmic layered sediments. These deposits are iron bound formations, consisting of distinct layers of iron and silica-rich minerals (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.
Showcase the cliff in 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 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 of the origin of the various scales of periodic and recurring patterns. (Opens in a new tab) 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 cycles 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. (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 of time.
A major example of the effect of the Milankovitch climate effect in the past is the occurrence of extreme cold (Opens in a new tab) or warm periods (Opens in a new tab)as well as more humid (Opens in a new tab) Or dry 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 are the interpretation of the periodic greening of the Saharan desert (Opens in a new tab) Low levels of oxygen in the deep ocean (Opens in a new tab). Milankovitch cycles also influenced the migration and evolution of plants and animals (Opens in a new tab) Including our human race (Opens in a new tab).
The fingerprints of these changes can be read through periodic changes in sedimentary rocks (Opens in a new tab).
The distance between the Earth and the Moon is directly related to the frequency of one of the Milankovitch cycles – the climatic precession cycle (Opens in a new tab). This cycle arises from the preliminary motion (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.
Our previous research showed that Milankovitch cycles could be preserved in an ancient-scale iron formation in South Africa (Opens in a new tab)thus supporting Trendall’s theory.
It is possible that the banded iron formations in Australia were 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 in Australian rocks are better exposed, allowing us to study the variations at much higher resolution.
Our analysis of Australian banded iron formation showed that the rocks contain multiple scales of periodic variations that repeat approximately at 4 and 33 inches (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 precession signal to calculate the distance between Earth and the Moon 2.46 billion years ago (Opens in a new tab).
We found that the Moon was closer to Earth by about 37,280 miles (60,000 km) (that distance is about 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.
Understanding the dynamics of the solar system
Research in astronomy has provided models for the formation of our solar system (Opens in a new tab)Current conditions notes (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 it will be necessary for future models of the Earth-Moon system (Opens in a new tab).
It is really amazing that the dynamics of the past solar system can be determined by small differences in 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.
This article has been republished from Conversation (Opens in a new tab) Under Creative Commons License. Read the original article (Opens in a new tab).
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