Watch the video: Boring billion – why days on earth once had 19 hours.
There are 24 hours in a day on earth, but that wasn’t always the case.
There was a time when the Earth took only 19 hours to rotate.
This period, around 1.8 billion years ago, lasted a billion years and is called the “boring billion”.
“Boring” because relatively little happened in terms of the evolution of life during that time.
The reduction in day length is said to have occurred one to two billion years ago. The researchers Ross N. Mitchell and Uwe Kirscher assume that the formation of an ozone layer and the associated atmospheric “solar tides” have put the earth in the 19-hour rhythm.
At that time, the moon was at a constant distance from the earth and was closer to the blue planet than it is today.
In June 2023, researchers will publish a study that explains that Earth’s satellite gradually “stole the Earth’s rotational energy”. (“Mid-Proterozoic day length stalled by tidal resonance”, 12 June 2023, Nature Geoscience)
The moon moved away from the earth, slowing down the speed of the earth’s rotation. This change was an extremely slow process: It is estimated that the days per year only became about 0.000015 seconds longer. Even today, the distance to the moon continues to grow. Every year three to four centimeters are added. As a result, the days are getting longer – by 2.3 milliseconds every century.
An important building block for the emergence of life on earth: longer days – i.e. more light – would have enabled photosynthetic bacteria to increase the oxygen content on earth. According to the researchers, this made it possible for more complex life to emerge.
The basis for the work of the researchers Ross N. Mitchell and Uwe Kirscher is the analysis of limestone deposits and patterns of mud sediments preserved in stone.