It is a perceived constant in our lives, the day and its 24 hours. But the earth's rotation as its basis is not specified anywhere. It is the result of billions of years of development and is changeable. Even we as humanity are already pulling the brake lever with today's technology.
Already 20 years ago there was oneNASA calculationshowed that one particular construction project particularly stands out: the Three Gorges Dam in China.
The earth is literally spreading its arms
Before every dam can generate electricity through the controlled flow of water, it is primarily one thing: a huge reservoir. Depending on the height of the dam and, above all, the geography of the region, artificial lakes of different volumes build up in the mountains upstream in front of them.
In the case of the Three Gorges Dam in China, this is a maximum of around 40 cubic kilometers. For comparison: Lake Constance in Germany has a volume of around 48 cubic kilometers (viaThurgau Environment OfficeandThe Three Gorges Dam – a sustainable undertaking?
).
From a physical point of view, this represents nothing other than a shift of mass outwards. Imagine an ice skater. If he turns and pulls the initially outstretched arms towards his body during a turn, his rotation accelerates - this also works in the opposite direction. The physical key word to read is: conservation of angular momentum.
Mathematically speaking, any transfer of mass away from the center of the Earth slows down the rotation and thus lengthens the Earth's day. According to the researchers, these changes could hardly be measured.
Because the time required for one revolution would itselfat maximum fillingof the reservoir in China will decrease by only 0.06 microseconds, writes NASA. This maximum water load is usually not reached (viaCNN). A day currently lasts 86.4 billion microseconds.
Earthquakes as the main brake
However, the forces in the Earth's mantle easily dwarf our unintentional efforts. The earthquake before Christmas in Sumatra in 2004 caused such enormous masses that, according to NASA data, it should have resulted in a day lengthening of 2.68 microseconds.
The record earthquake in 2004 was also the impetus for the researchers' calculations at the time, because it isaccording to the Federal Statistical OfficeWith its 9.1 on the Richter scale, it was the third strongest earthquake recorded on Earth between 1900 and 2023. It also caused the deadliest tsunami ever directly observed. It devastated large parts of the Indian Ocean coast and killed around 230,000 people (viaWelthungerhilfe).
Ultimately, it doesn't matter to the planet what causes the masses to shift. At some point in the future, as a result of human actions and inexorable changes caused by plate tectonics, a leap second may become necessary. Because the effects add up over thousands of years.
