The Earth and the Moon haven't always been where they are today. In fact, at this very moment, they are moving. And not only in the classic movements of rotation and revolution, but our world is also gradually moving away from the Sun, and our satellite from us. This means that millions of years ago, days on Earth were much shorter than they are now, and the Moon appeared larger in the night sky. But going back in time on a geologically active planet is quite a challenge. Now, an international team has managed to precisely determine the distance to the Moon 2.46 billion years ago, using what are known as Milankovitch cycles. The findings have just been published in the Proceedings of the National Academy of Sciences (PNAS). Just as the Earth's movement around the Sun determines the seasons, and its rotation on its axis determines day and night, its distance from our star also generates cycles. These are much longer and more subtle, resulting in, for example, glacial and interglacial periods. These are known as Milankovitch cycles. Climate changes, in turn, can be reflected on the Earth's surface. In their search for these cycles, the team, led by researchers from Utrecht University, the University of Geneva, and the University of Quebec in Montreal, observed a very old type of sedimentary rock at Joffre Cliff in Karijini National Park, Australia, known as banded iron formations (BIFs). BIFs are rocks with characteristic iron-rich layers that were widely deposited on the ocean floor millions of years ago. They can now be found in some of the oldest existing parts of the Earth's crust and studied, as they provide important information about the Earth's past. And, although it was previously thought that the deposition of these iron formations and their regular stratification were mainly due to increased submarine volcanic activity, the hydrothermal source of the iron, the team led by Margriet Lantink of Utrecht University, and first author of the study, managed in a previous study to link for the first time the regular alternations in banded iron formations (BIFs) with cyclical changes in Earth's orbit around the Sun. Based on this, they have been able to get much more out of these Australian BIFs. "In the Australian deposits, a regular pattern of iron-rich layers alternating with layers containing more clay was found," the authors explain in a statement. According to the researchers, this characteristic pattern is related to periodic changes in the shape of Earth's orbit and the orientation of its rotational axis, which in turn influenced the distribution of solar radiation received by Earth and, therefore, also the climate. These climatic fluctuations were subsequently recorded as cyclical patterns in the geological record. Furthermore, the Moon's distance also influenced this pattern, as the tidal system was different (our satellite being closer). Through in-depth analysis of the alternating rock patterns (some harder and reddish-brown, others softer and darker, like clay), scientists were able to reconstruct the distance between the Earth and the Moon when these sediments were deposited there, exactly 2.46 billion years ago. "Today, this distance averages around 384,300 kilometers, since the Moon doesn't orbit the Earth in a perfect circle; its orbit is an ellipse. However, from these patterns, we can infer that during the time period we studied, 2.46 billion years ago, the distance was much shorter: around 321,800 kilometers," Lantink points out. This estimate agrees with recent parallel studies of the Earth-Moon system's history. "It's also important to note that our interpretation of the patterns in the rock strata in terms of Milankovitch cycles was confirmed by uranium-lead dating of volcanic minerals in the rock samples," Lantink adds. Over time, Earth's rotation around its axis has also slowed. While this was already known, Lantink's team has now found a way to establish how long a day was on early Earth: 17 hours. Climate change doesn't come from space. In the aforementioned study he conducted with colleagues from Switzerland (and published in 'Nature Geosciences'), Lantink already demonstrated that Earth's climate underwent regular changes 2.5 billion years ago due to periodic changes in the shape of Earth's orbit. Because billions of years ago, conditions on Earth were radically different from today: there was still no free oxygen in the atmosphere, volcanic activity was more violent, and vegetation and multicellular life had not yet developed. But we should also consider fluctuations in Earth's orbit and axis, which could have affected the climate at that time and, therefore, possibly the early biosphere and the chemical composition of the oceans. MORE INFORMATION News Not Spectacular: The Pillars of Creation, seen like never before by James Webb News Yes They observe how a black hole 'vomits' the remains of a star three years after devouring it. Even so, the researcher points out that current climate change is not a consequence of the movement of the Earth or the Moon: "It is happening on much shorter timescales, and humans are responsible for it."
