Jakarta –
Gazing at the Moon from Earth seems to look the same. Without realizing it, it turns out that this natural satellite of the Earth is slowly moving away from Earth.
In 1969, NASA’s Apollo mission installed reflective panels on the Moon. This reflective panel shows that the Moon is moving 3.8 cm away from Earth each year.
The research was conducted by Joshua Davies, professor at Sciences de la Terre et de l’atmosphère, Université du Québec à Montréal (UQAM), Canada, and colleague Margriet Lantink, Associate Research Postdoctoral, Department of Geoscience, University of Wisconsin-Madison, USA.
“If we took the current pace of the Moon’s recession and projected it back into the past, it would have culminated in a collision event between Earth and the Moon about 1.5 billion years ago,” Davies and Lantink wrote. The Conversation.
“However, the Moon formed about 4.5 billion years ago, which means the current recession rate is a poor guide to the past,” he continued.
Together with other research colleagues from Utrecht University and the University of Geneva, Davies and Lantink used a combination of techniques to obtain information about our Solar System’s past.
“We have recently found the perfect place to uncover the long-term history of the Moon receding. And that is not from studying the Moon itself, but from reading signals in ancient rock layers on Earth,” they wrote.
Examining the Rock Layers
In the beautiful Karijini National Park in western Australia, several gorges cut through rhythmically layered 2.5 billion year old sediments. These sediments are layered iron formations, consisting of special layers of iron- and silica-rich minerals that were once deposited extensively on the ocean floor and are now found in the oldest parts of the Earth’s crust.
A cliff exposure at Joffre Falls shows how layers of reddish-brown iron formations less than a meter thick are alternated, at regular intervals, by darker, thinner horizons.
The darker intervals consist of softer rock types that are more prone to erosion. Closer examination of the outcrops reveals more regular small-scale variation. The surface of the rocks, which have been polished by the waters of a seasonal river that flows through the gorge, reveals a pattern of alternating layers of white, reddish, and bluish-grey.
In 1972, Australian geologist AF Trendall posed questions about the origin of the various cyclical scales, the repeating patterns seen in these ancient rock layers. He suggested that the pattern might be related to past climate variations caused by the so-called ‘Milankovitch cycles’.
Cyclical Climate Change
The Milankovitch cycle describes how slight periodic changes in the shape of the Earth’s orbit and the orientation of its axis affect the distribution of sunlight Earth receives over a number of years.
Currently, the dominant Milankovitch cycle changes every 400,000 years, 100,000 years, 41,000 years and 21,000 years. These variations exert powerful control over our climate over long periods of time.
A prime example of the forcing influence of Milankovitch climate in the past is the occurrence of periods of extreme cold or warm, as well as wetter or drier regional climatic conditions.
This climate change has significantly changed conditions on the Earth’s surface, such as the size of lakes. They are the explanation for how the periodic greening of the Sahara desert and low oxygen levels in the deep ocean occurs. The Milankovitch cycle also influences the migration and evolution of flora and fauna including our own species. Signs of this change can be read through the cyclical changes in sedimentary rocks.
(rns/rns)
