looking up Moon in the night sky, you would never imagine that it is slowly moving away from Earth. But we know otherwise. In 1969, NASA’s Apollo missions installed reflective panels on the Moon. These have shown that the Moon is It is currently moving 3.8 centimeters away from Earth each year..
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. However, the Moon was formed about 4.5 billion years agowhich means that the current recession rate is a poor guide to the past.
Together with our fellow researchers from University of Utrecht and the University of Genevawe 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. Forks not from studying the Moon itself, but from reading signals in ancient rock layers on Earth.
reading between the layers
in the beautiful Karijini National Park 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 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 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 additional smaller-scale regular 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 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
Milankovitch cycles describe how small periodic changes in the shape of Earth’s orbit and the orientation of its axis influence the distribution of sunlight received by Earth 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 climate for long periods of time.
Key examples of the influence of Milankovitch climate forcing in the past are the occurrence of extremely cold either warm periodsas much as more wet or drier regional climatic conditions.
These climate changes have significantly altered conditions on the Earth’s surface, such as the size of the lakes. are the explanation of periodic greening of the Sahara desert Y low oxygen levels in the deep ocean. Milankovitch cycles have also influenced the migration and evolution of flora and fauna including our own kind.
And the signatures of these changes can be read Cyclical changes in sedimentary rocks.
registered oscillations
The distance between the Earth and the Moon is directly related to the frequency of one of the Milankovitch cycles: climatic precession cycle. 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 Earth.
This means that if we can first find Milankovitch cycles in ancient sediments and then find a signal from the Earth’s 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 may be preserved in an ancient banded iron formation in South Africathus supporting Trendall’s theory.
The banded iron formations in Australia were probably deposited in the same ocean 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 cyclical variations that repeat at roughly 10- and 85-centimeter 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.
Thus, our analysis suggested that the 11,000-year cycle observed in the rocks is likely 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.
We found that the Moon was about 60,000 kilometers closer to Earth at the time (that distance is about 1.5 times the circumference of 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 systemY observations of current conditions.
Our studio and some research by others represents one of the only methods to obtain real data on the evolution of our Solar System and will be crucial for future models of the Earth-Moon system.
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.
Joshua DavisProfessor, Sciences de la Terre et de l’atmosphere, University of Quebec in Montreal (UQAM) Y margriet latinkAssociate Postdoctoral Researcher, Department of Geosciences, University of Wisconsin-Madison
This article is republished from The conversation under a Creative Commons license. Read the Original article.
