Jakarta –
The days on Earth are slowly getting longer, thanks in large part to the Moon. However, it seems that this is a very different process than imagined. The day lengthening has stalled at least once.
For a long time starting about two billion years ago, the lengthening of Earth’s day may have stopped completely, driven by changes in Earth’s atmosphere. Meanwhile, the interaction between Earth and the Moon slowly pushes our satellite away in the process of slowing Earth’s spin.
“Over time, the Moon has stolen Earth’s rotational energy to push it into a higher orbit farther from Earth. The slower rotation definitely lengthens the day,” said study author Professor Ross Mitchell from the Chinese Academy of Sciences as quoted by IFL Science.
“Most models of the Earth’s rotation predict that day length is consistently shorter and shorter going back in time,” added study author Dr Uwe Kirscher from Curtin University.
Instead, Mitchell and Kirscher concluded that after the formation of the Moon, Earth’s days initially grew longer but then stopped for about 19 hours before the lengthening resumed.
Interestingly, only a few periods of no change occurred from two to a billion years ago. This coincided with an era that geologists call ‘billion years of dullness’ because so little had happened in the period before the sudden burst of multicellular life. Neither of them thought this was a coincidence.
The retrograde occurs because the Moon isn’t the only celestial body that influences our day. Heat from the Sun produces tides in the atmosphere, which speed up rotation. At this time, the Sun’s tides are much weaker than the Moon’s and only moderate the Moon’s effect.
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The 600 million year old sedimentary rock that preserves the Milankovitch cycle has been used to detect the length of the ancient Earth’s day.
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“However, as the Moon is closer, the frictional ‘coupling’ between Earth and Moon is weaker due to Earth’s faster rotation,” Mitchell said. “Tidal frequencies do not resonate with the Earth on a global scale, thereby impeding energy transfer,” he added.
Mitchell and Kirscher wondered if the Moon’s force might be so small temporarily that the Sun actually cancels it out, and their paper confirms this. Even with the Moon’s relative weakness, this required a stronger influence from the Sun, which the authors attribute to the composition of the atmosphere at a time when oxygen levels were low but ozone high.
“Solar tides are excited by the absorption of sunlight by water vapor and ozone,” Mitchell said. Only during the period between the Big Oxidation Event and the birth-stimulating increase in O2 was this possible.
Last day length measurements have traditionally relied on layers of fine sediment in ancient tidal mudflats. These can be so detailed that it is possible to calculate the number of days between monthly tidal cycles.
Some sites are clear enough to use this way, and even some of them are disputed, so we only have an idea of how long the day is at certain points.
Meanwhile, Mitchell and Kirscher used the Milankovitch cycle in Earth orbit. “The two Milankovitch cycles, precession and tilt, are related to the wobble and tilt of the Earth’s rotational axis in space. Therefore, the faster rotation of the early Earth can be detected in the shorter cycles of precession and tilt in the past,” said Kirscher.
Watch Video “Note! There will be a penumbral lunar eclipse on May 5 and 6, 2023“
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(rns/rns)
2023-06-14 14:15:30
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