Over the Past 2.5 billion years, our moon has been gradually moving away from Earth.

Over the Past 2.5 Billion Years, Our Moon Has Been Gradually Moving Away From Earth

(new tab opens) The source contributed the article to Expert Voices: Op-Ed & Insights on Space.com.

Professor of Earth and atmospheric sciences Joshua Davies, University of Quebec at Montréal (UQAM)

University of Wisconsin-Madison Department of Geoscience Postdoctoral Research Associate Margriet Lantink

You would never guess from looking up at the moon in the night sky that it is progressively relocating away from Earth. However, we are aware that this is false. The Apollo missions of NASA placed reflecting panels on the moon in 1969. These have demonstrated the moon’s present distance from Earth, which is 3.8 centimetres every year (opens in new tab).

If we extrapolate back in time using the moon’s present rate of recession, we arrive at a collision between the Earth and moon that occurred roughly 1.5 billion years ago (opens in new tab). However, the moon was created about 4.5 billion years ago(opens in new tab), therefore the recession rate today is a bad indicator of what happened in the past.

We have been utilising a variety of methodologies, together with our colleagues from the Universities of Utrecht and Geneva, to attempt and learn more about the distant past of our solar system.

We’ve just found the ideal location for studying the long-term evolution of our waning moon. And it comes from reading signals in old layers of Earthly rock, not from analysing the moon itself (opens in new tab).

Some gorges in western Australia’s stunning Karijini National Park(opens in new tab) cut through strata that are 2.5 billion years old and stacked rhythmically. These sediments are banded iron formations, which are layers of silica- and iron-rich minerals that were formerly extensively distributed on the ocean floor and are today found on the oldest regions of the Earth’s crust.

Cliff exposures at Joffre Falls(opens in new tab) demonstrate the regular alternation of darker, thinner horizons with layers of reddish-brown iron deposit that are slightly under a metre thick.

Over the Past 2.5 Billion Years, Our Moon Has Been Gradually Moving Away From Earth

A softer rock type that is more prone to erosion makes up the darker intervals. The outcrops also contain an extra regular, smaller-scale variation, which is seen when examining them more closely. The gorge’s seasonal river water has polished the rock surfaces, revealing a pattern of alternating white, reddish, and blueish-gray strata.

The subject of the genesis of the various scales of cyclical, repeating patterns(opens in new tab) observed in these ancient rock layers was first posed by Australian geologist A.F. Trendall in 1972. He hypothesised that the patterns might be connected to earlier climate variations brought on by so-called “Milankovitch cycles.”

The Milankovitch cycles explain how minute, cyclical variations in the Earth’s orbital parameters and axis orientation affect how much sunlight the planet receives over the course of years.

Currently, there are four prominent Milankovitch cycles that shift every 400,000, 100,000, 41,000, and 21,000 years. Our climate is strongly influenced by these shifts over extended time periods.

Extreme cold (opens in new tab) or warm periods, as well as wetter (opens in new tab) or dryer regional climate conditions, are a few prominent examples of Milankovitch climate forcing’s influence in the past.

The conditions on Earth’s surface, such as lake size, have drastically changed as a result of these climate changes (opens in new tab). They are the cause of the Saharan desert’s recurring greening (opens in new tab) and the deep ocean’s low oxygen levels (opens in new tab). The migration and evolution of flora and animals, including our own species, have been influenced by Milankovitch cycles (opens in new tab).

Additionally, cyclical variations in sedimentary rocks can be used to detect the effects of these changes (opens in new tab).

The climatic precession cycle, one of the Milankovitch cycles, has a direct relationship with the distance between the Earth and the moon (opens in new tab). This cycle results from the Earth’s spin axis’s precessional motion (wobble) or changing orientation throughout time. Although this cycle currently lasts about 21,000 years, it used to last less time when the moon was closer to Earth.

The distance between the Earth and the moon at the time the sediments were formed can therefore be calculated if we can first identify Milankovitch cycles in old sediments, then identify a sign of the Earth’s wobble, and finally determine its period.

Our earlier studies supported Trendall’s hypothesis by demonstrating that Milankovitch cycles might be maintained in an old banded iron formation in South Africa(opens in new tab).

Over the Past 2.5 Billion Years, Our Moon Has Been Gradually Moving Away From Earth

Around 2.5 billion years ago, the banded iron formations in Australia(opens in new tab) were likely deposited in the same ocean as the rocks in South Africa. But because the cyclic variations in Australian rocks are more clearly visible, we can analyse the variations much more thoroughly.

Our examination of the Australian banded iron formation revealed that the rocks featured numerous cycle scales that roughly repeated at 4 and 33 inch intervals (10 and 85 cm intervals). We discovered that these cyclical fluctuations took place around every 11,000 and 100,000 years when we combined these thicknesses with the rate at which the sediments were deposited.

Because the climatic precession cycle has a significantly shorter time than the present 21,000 years, our analysis indicated that the 11,000 cycle seen in the rocks is probably related to it. We then calculated the separation between Earth and the moon 2.46 billion years ago using this precession signal (opens in new tab).

The moon was approximately 37,280 miles (60,000 kilometres) closer to the Earth when we discovered this (that distance is about 1.5 times the circumference of Earth). As a result, a day would be significantly shorter than it is right now, lasting approximately 17 hours as opposed to the 24 it does right now.

the dynamics of the solar system

Models for the creation of our solar system and observations of the present state of the universe have been made possible by astronomical research (opens in new tab).

Future Earth-moon system models will be extremely dependent on the results of our study and some other research(opens in new tab), which represents one of the few ways to gather accurate information on the development of our solar system (opens in new tab).

The ability to infer previous solar system dynamics from minute differences in prehistoric sedimentary rocks is truly astonishing. The evolution of the Earth-moon system cannot, however, be fully understood on the basis of one significant data point.

To follow the evolution of the moon across time, we now require additional trustworthy data and fresh modelling techniques. Additionally, our study team has already started looking for the next collection of rocks that may provide us with additional information about the solar system’s past.

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