This article was originally published on The conversion. (opens in a new tab) Post contributed article to Space.com’s Expert Voices: Opinion and Perspectives.
Joshua Davis (opens in a new tab)Professor of Earth and Atmospheric Sciences, Université du Québec à Montréal (UQAM)
margriet latink (opens in a new tab)Postdoctoral Research Associate, Department of Geosciences, University of Wisconsin-Madison
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. In 1969, NASA apollo missions installed reflective panels on the moon. These have shown that Moon it is currently moves 3.8 cm away from Earth every year (opens in a new tab).
If we take the current rate of recession of the moon and project it back in time, we 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 a poor guide to the past.
Together with our fellow researchers from University of Utrecht (opens in a new tab) and the University of Geneva (opens in a new tab)We have been using a combination of techniques to try to gain insight into our solar system’s distant past.
We recently discovered the perfect place to discover the long-term history of our receding moon. And it is not for studying the moon itself, but for reading signals in ancient rock layers on Earth (opens in a new tab).
related: How was the moon formed?
reading between the layers
in the beautiful Karijini National Park (opens in a new tab) in western Australia, some gorges cut through 2.5-billion-year-old rhythmically layered sediments. These sediments are banded iron formations, comprising layers of minerals rich in iron and silica (opens in a new tab) once widely deposited on the ocean floor and is now found in the oldest parts of the earth’s crust.
cliff exposures in Cascades of Joffre (opens in a new tab) they show how reddish-brown iron-forming layers just under a meter thick alternate, at regular intervals, with thinner, darker horizons.
The darker intervals are made up of a softer type of rock that is more susceptible to erosion. A closer look at the outcrops reveals the presence of additionally regular, smaller-scale variation. The rocky surfaces, which have been polished by the seasonal water of the river that flows through the gorge, reveal a pattern of alternating layers of white, reddish and blue-grey.
In 1972, the Australian geologist AF Trendall raised the question of the origin of the different scales of cyclical and recurring patterns (opens in a new tab) visible in these ancient rock layers. He suggested that the patterns might be related to past climatic variations induced by so-called “Milankovitch cycles.”
cyclical climate changes
The Milankovitch cycles describe how small periodic changes in the shape of the Earth’s orbit and the orientation of its axis influence the distribution of sunlight received by the Earth (opens in a new tab) throughout the years.
At this time, the dominant Milankovitch cycles change every 400,000 years, 100,000 years, 41,000 years, and 21,000 years. These variations exert a strong control over our weather for long periods of time.
Key examples of the influence of Milankovitch climate forcing in the past are the occurrence of extremely cold (opens in a new tab) either warm periods (opens in a new tab)as much as climate (opens in a new tab) or drier regional climatic conditions.
These climate changes have significantly altered conditions on the Earth’s surface, such as the size of the lakes (opens in a new tab). are the explanation of periodic greening of the Sahara desert (opens in a new tab) Y low oxygen levels in the deep ocean (opens in a new tab). Milankovitch cycles have also influenced the migration and evolution of flora and fauna (opens in a new tab) including our own kind (opens in a new tab).
And the signatures of these changes can be read cyclical 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: climatic precession cycle (opens in a new tab). This cycle arises from the movement of precession (wobble) or the change in orientation of the Earth’s spin axis over time. This cycle currently lasts ~21,000 years, but this period would have been shorter in the past when the moon was closer to Land.
This means that if we can first find Milankovitch cycles in ancient sediments and then find a signal from the Earth wobble and establish its period, we can estimate the distance between the Earth and the Moon at the time the sediments were deposited.
Our previous research showed that Milankovitch cycles can be preserved in an ancient banded iron 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 cyclical 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 contained multiple scales of cyclic variations that repeat at roughly 4- and 33-inch (10 and 85-cm) intervals. Combining these thicknesses with the rate at which the sediments were deposited, we found that these cyclical variations occurred approximately every 11,000 years and 100,000 years.
Therefore, our analysis suggested that the 11,000 cycle observed in the rocks is probably related to the climatic precession cycle, which has a much shorter period than the current ~21,000 years. We then use this precession signal to calculate the distance between the earth and the moon 2460 million years ago (opens in a new tab).
We found that the moon was about 37,280 miles (60,000 kilometers) closer to Earth at the time (that distance is about 1.5 times the distance). circumference of the earth). This would make the length of a day much shorter than it is now, 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)Y observations of current conditions (opens in a new tab).
Our studio and some research by others (opens in a new tab) represents one of the only methods to obtain real data on the evolution of our solar system, and it will be crucial for future models of the Earth-Moon system (opens in a new tab).
It is quite surprising that the dynamics of the solar system of the past 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.
We now need other reliable data and new modeling approaches to track the evolution of the moon through time. And our research team has already begun the search for the next set of rocks that may help us uncover more clues about the history of the solar system.
This article is republished from The conversation (opens in a new tab) under a Creative Commons license. Read the Original article (opens in a new tab).
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