An Earth day lasted just 19.5 hours for a billion years

A slow, steady day on Earth has been interrupted by the pull of the moon for more than a billion years, according to a study by University of Toronto scientists.

The reason? The atmospheric tide caused by the Sun balanced the impact of the Moon, from about two billion years ago to 600 million years ago. This event has stabilized the speed of the Earth’s rotation so that a day lasts only 19.5 hours.

Without this billion-year pause in slowing down our planet’s rotation, our current 24-hour day would last more than 60 hours.Astrophysicist Norman Murray and his colleagues explain in their work published in the journal Scientific advances (new window) (in English).

earth day

When the Moon formed about 4.5 billion years ago, the Earth day lasted less than 10 hours. But since a natural satellite arrives in Earth’s sky, the moon’s pull on the planet slows its rotation, resulting in longer and longer days.

Even today, the day continues to lengthen at a rate of 1.7 milliseconds per century.

The Moon slows down the rotation of the planet pulling Earth’s oceans, form inflammation A phenomenon where tides on opposite sides of the Earth take the form of high and low tides.

In these bulges the Moon’s gravity and the friction between the tides and the ocean floor act as a brake on the planet’s rotational speed. gold, Sunlight creates this type of bulge, but instead of slowing down Earth’s rotation, it speeds it up.Professor Murray says.

For most of Earth’s evolution, this atmospheric vibration was out of sync with the planet’s rotational speed. Today, each Two atmospheric high tides It takes 22.8 hours to go around the world. Because this vibration and the Earth’s 24-hour rotation period are out of sync, the atmospheric wave is relatively weak.

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Under the influence of the Sun

The Ontario team combined geologic data and global atmospheric circulation models to predict the temperature of the atmosphere over a billion-year period, assuming the atmosphere warmed and resonated for about 10 hours. Also, at the beginning of this epoch, the rotation of the Earth – slowed by the Moon – reached 20 hours.

When the atmospheric oscillation and day length became equal factors (10 and 20), the atmospheric tide strengthened, swelling increased, and the tidal effect of the Sun became large enough to counteract the lunar tide.

The tidal deadlock between the Sun and the Moon is the result of an incidental, but very important, connection between the temperature of the atmosphere and the rate of rotation of the Earth.Researchers write.

For most of Earth’s geological evolution, lunar tides were ten times greater than solar tides, slowing Earth’s rotation and lengthening day length.They mention.

However, about two billion years ago, atmospheric inflation was larger because the atmosphere was warmer and its natural vibration—the frequency at which waves travel—matched the length of the day.

Climate changes

The models used in this work are the same ones used by climate scientists to study global warming. According to Murray, the truth is that they worked well in his research A timely lesson.

According to him, although remote in geologic history, the changing atmospheric resonance with temperature adds further perspective to the current climate crisis. Thus, the warming of the atmosphere may have effects on the balance of the tides.

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