This article was originally published here Conversation. (opens in new tab) The publication submitted the article to Space.com Expert Voices: Op-Ed & Insights.
Joshua Davies (opens in new tab)Professor of Earth and Atmospheric Sciences, Université du Québec à Montréal (UQAM)
Margriet Lantinck (opens in new tab)Postdoctoral Research Fellow, Department of Geology, University of Wisconsin–Madison
When you look at the moon in the night sky, you would never imagine that it is slowly moving away from the Earth. But we know otherwise. NASA in 1969 Apollo missions installed reflective panels on the moon. They showed that month does it is currently moving 3.8 cm away from Earth every year (opens in new tab).
If we take the Moon’s current declination rate and project it backwards, we end up with a The collision of the Earth and the Moon about 1.5 billion years ago (opens in new tab). However, the moon was formed about 4.5 billion years ago (opens in new tab)meaning that the current rate of decline is a poor guide to the past.
together with our fellow researchers from University of Utrecht (opens in new tab) and University of Geneva (opens in new tab)we use a variety of methods to learn about the distant past of our solar system.
We discovered the perfect place to uncover the long history of our recently departed moon. And this is not from studying the moon itself, but from it Reading signals in ancient rock layers on Earth (opens in new tab).
Related: How was the moon formed?
Reading between the layers
In beautiful Karijini National Park (opens in new tab) In western Australia, some canyons cut 2.5 billion-year-old rhythmically layered sediments. These deposits are characteristic banded iron compounds layers of minerals rich in iron and silica (opens in new tab) once widely deposited on the ocean floor and now found in the oldest parts of the Earth’s crust.
Cliff expositions Joffre Falls (opens in new tab) show how layers of red-brown iron formation, less than a meter thick, regularly alternate with darker, thinner horizons.
The dark intervals consist of a softer rock type that is more susceptible to erosion. A closer look at the outputs reveals the presence of additional regular, smaller-scale variation. Polished by the seasonal river waters flowing through the gorge, the rock surfaces reveal a pattern of alternating white, red and blue-gray layers.
In 1972, Australian geologist AFTrendall raised the question of the origin of soil various scales of periodic, repeating patterns (opens in new tab) it appears in ancient rock formations. I suggested that the patterns could be related to past changes in climate called “Milankovitch cycles”.
Cyclical climate changes
Milankovitch periods describe small, periodic changes in the shape of Earth’s orbit and the orientation of its axis. It affects the distribution of sunlight received by the Earth (opens in new tab) over the years.
Currently, the dominant Milankovitch cycles vary every 400,000 years, 100,000 years, 41,000 years, and 21,000 years. These variations are powerful controls our climate over a long period of time.
The main examples of the influence of the Milankovitch climate forcing in the past are the occurrences extremely cold (opens in new tab) gold warm periods (opens in new tab)as well as water (opens in new tab) or drier regional climatic conditions.
These climate changes significantly changed conditions on Earth’s surface, e.g the size of the lakes (opens in new tab). They are the explanation for it Periodic greening of the Sahara desert (opens in new tab) and low oxygen levels in the deep ocean (opens in new tab). Milankovitch periods also affected migration and evolution of flora and fauna (opens in new tab) including ours own species (opens in new tab).
And the signatures of these changes can be read cyclic changes in sedimentary rocks (opens in new tab).
The distance between the Earth and the Moon is directly related to the frequency of one of the Milankovitch periods – climate precession period (opens in new tab). This cycle is caused by the precessional movement (wobble) or change of the Earth’s axis of rotation over time. Currently this period is ~21,000 years, but in the past the period would have been shorter when the Moon was closer. Place.
This means that if we can first find the Milankovitch cycles in the old sediments, and then find and determine the period of the Earth’s wobble signal, we can estimate the distance between the Earth and the Moon at the time the sediments were deposited.
Our previous studies have shown that there can be Milankovitch cycles It is preserved in an ancient banded iron formation in South Africa (opens in new tab)thus supporting Trendall’s theory.
The banded iron joints in Australia probably were lies in the same ocean (opens in new tab) Like the rocks of South Africa, about 2.5 billion years ago. However, the cyclical changes in Australian rocks are better exposed, allowing the changes to be studied with greater precision.
Our analysis of the Australian banded iron formation showed that the rocks have many periodic variations, repeated at approximately 4 and 33 inches (10 and 85 cm intervals). Combining these thicknesses with the rate of sediment deposition, we found that these cyclical changes occur approximately every 11,000 and 100,000 years.
Therefore, our analysis suggested that the 11,000-year period observed in the rocks is likely related to a period of climate precession with a shorter duration than the current ~21,000 years. We then used this precession signal Calculate the distance between the Earth and the Moon 2.46 billion years ago (opens in new tab).
We found that the Moon was then about 37,280 miles (60,000 kilometers) closer to Earth (about 1.5 times that distance). The circumference of the earth). This would make the length of a day shorter than it is now, about 17 hours rather than the current 24 hours.
Understanding the dynamics of the solar system
He provided models for research in astronomy the formation of our solar system (opens in new tab)and observations of existing conditions (opens in new tab).
Our education and some research by others (opens in new tab) It represents one of the only methods of obtaining real information about the evolution of our solar system and Future models of the Earth-Moon system (opens in new tab).
Determining the dynamics of the past solar system from small changes in ancient sedimentary rocks is quite surprising. 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 follow the moon’s evolution over time. Our research team has already begun searching for the next set of rocks that could help uncover more clues about the history of the solar system.
This article is being republished Conversation (opens in new tab) Under Creative Commons license. read it original article (opens in new tab).
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