How the Moon lengthens the days on Earth

Billions of years ago, the average length of an Earth day was less than 13 hours.

Since then it has been slowly lengthening and continues to do so, for a reason that involves the Moon and our oceans.

Throughout human history, the Moon has been a ghostly and inextricable presence on Earth.

Its gentle gravitational pull sets the rhythm of the tides and its pale light illuminates the nocturnal life of many species.

Entire civilizations have set their calendars according to the movements of the satellite and some animals, such as dung beetles, are guided by sunlight reflected on the surface of the Moon.

More importantly, the Moon may have helped create the conditions that make life on our planet possible, according to some theories, and even may have fueled the emergence of life on earth.

And its eccentric orbit around the blue planet is believed to influence some of the weather systems that shape our lives today.

But the Moon is also moving further and further away from us.

As it rotates around the Earth – its rotation and translation are synchronous and that is why we only see one face – the Moon is gradually moving away from our planet in a process known as “lunar recession.”

By projecting lasers from reflectors placed on the lunar surface by Apollo astronauts, scientists have recently been able to measure with millimeter precision how quickly the satellite is separating.

They confirmed that the Moon is moving away at a rate of 3.8 cm each year. And, as this happens, our days get a little longer.

“It’s all about the tides,” says David Waltham, a professor of geophysics at Royal Holloway (University of London) who studies the relationship between the Earth and its satellite.

“Tidal resistance on Earth slows down its rotation, and the Moon gains that energy in the form of angular momentum,” he explains.

Essentially, as the Earth rotates, the gravity of the Moon orbiting above it pulls on the oceans creating high and low tides.

In fact, these tides They are a “mass” of water which extends in an elliptical shape both towards and away from the Moon’s gravity.

But the Earth rotates on its axis much faster than the Moon orbits above it, meaning that friction from the ocean basins moving below also acts, dragging water along.

This means that the “mole” of water moves slightly in front of the Moon in its orbit, which tries to push it back.

This slowly depletes our planet’s rotational energy, slowing its spin while the Moon gains energy and thus height in its orbit.

This progressive slowdown in the rotation of our planet represents an increase in the length of an average Earth day of approximately 1.09 milliseconds per century since the end of the 17th century, according to the latest analysis.

Other estimates put the figure slightly higher, at 1.78 ms per century, from observations of previous eclipses.

Although it seems insignificant, over the years 4.5 billion years of Earth history It has meant an important change.

It is believed that the Moon formed approximately in the first 50 million years after the birth of the Solar System.

The most widely accepted theory is that a collision between the Earth in its embryonic phase and another Mars-sized object, known as Theia, dislodged a fragment of material and debris that coalesced into what we now call the Moon.

What is clear from geological data preserved in bands of rock on Earth is that the Moon was much closer to our planet in the past than it is today.

The Moon is currently 384,400 kilometers from Earth.

A recent study suggests that about 3.2 billion years ago (just when the tectonic plates began to move and the microorganisms that lived in the oceans were devouring nitrogen) at “only” 270,000 kilometers.

“The Earth, which rotates faster, had a shorter day, so in a 24-hour period there were two sunrises and two sunsets“says Tom Eulenfeld, a geophysicist who led the study at Friedrich Schiller University in Jena, Germany.

And he adds that “this may have reduced the temperature difference between day and night and affected the biochemistry of photosynthetic organisms.”

However, studies like theirs reveal that the rate of lunar recess has not been constant either: it has accelerated and slowed down over time.

A study carried out by Vanina López de Azarevich, a geologist at the National University of Salta in Argentina, suggests that about 550-625 million years ago the Moon could move as far away as 2.8 inches (7 cm) per year.

“The speed at which the Moon was moving away from the Earth definitely changed over time and will do so in the future,” Eulenfeld says.

However, for much of its history the Moon has receded at a much slower rate than today.

In fact, we currently live in a period in which the rate of recession is unusually high: the Moon would only have had to move away at the current rate for 1.5 billion years to reach the position you are in today.

But this process has been happening since the Moon formed 4.5 billion years ago, which indicates that at times in the past it was slower.

“At the moment tidal resistance is three times greater than you would expect,” says Waltham.

This is attributed to the Atlantic Ocean.

According to the current configuration of the continents, the North Atlantic basin has the precise proportions to generate a resonance effect, so the water it contains moves back and forth at a rate similar to that of the tides.

This means that the tides are bigger. As Waltham illustrates, think about pushing a child on a swing: he goes higher if each push is synchronized with the existing movement.

“If the North Atlantic were slightly wider or narrower, this wouldn’t happen,” says Waltham. “The models seem to show that if we go back a few million years, the tidal force was less because the continents were in different positions.”

But this is likely to continue to change in the future. Models predict that a new tidal resonance will appear in 150 million years and then disappear in about 250 million years, when a new “supercontinent” forms.

So could there be a future where the Earth no longer has a Moon?

Even at its current high rate of recess, the Moon is unlikely to leave Earth completely.

The disappearance of the Sun will probably occur long before that happens, within about 5,000 to 10,000 million yearsand humanity was likely extinct long before then.

However, in the short term, humanity itself can contribute to lengthening the days a little more, by reducing the amount of water trapped in glaciers and polar caps with the melting caused by climate change.

“The ice basically suppresses the tides,” Waltham says, noting that about 600-900 million years agowhen our planet is believed to have entered a particularly icy period, there was a dramatic slowdown in the rate of lunar recess.

However, the impact is difficult to predict, as some of this will be offset by the bouncing of land masses as the weight of ice sheets is taken off them, and other complications.

In theory, the next generation of astronauts who will fly to the Moon with NASA’s Artemis program will be able to say they saw their planet from further away than their Apollo program predecessors did 60 years ago (although the Moon’s elliptical orbit around Earth will probably determine this to a greater extent, since the distance varies by 43,000 km every 29 days).

As for the rest of us, our lives will have been too short to notice the billionths of a second that are added to the length of each passing day.

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