1.4 billion years ago, the Earth day lasted only 18 hours. The main reason was that the Moon was closer to our planet, so it accelerated the speed with which it rotated on its axis. Things of gravity.
But our satellite, which orbits us at an average distance of 384,400 kilometers, is gradually moving away from us. Specifically, 3.82 centimeters per year. And that implies that the Earth’s rotation is slowing down, according to a study done at the University of Wisconsin-Madison, United States.
How do you know the days are getting longer?
Stephen Meyers, professor of Earth Sciences at that university and co-author of the work, explains that they have reached such a conclusion thanks to astrochronology, a method that unites astronomy with geological observations and that allows us to look at the past of the planet and the System Solar, and study the climatic changes from the traces that these leave in the oldest rocks.
The movement of the Earth in space is influenced by other celestial bodies – the Moon, the planets of the Solar System … – that exert their force on it. This complex game of gravitational attractions alters the Earth’s rotation, the inclination of its axis and the orbit that our home follows around the Sun.
These variations are called Milankovitch cycles, and they mark the amount of solar radiation that reaches us, the essential factor to explain climatic variations, which leave geological clues. According to Meyers, studying these clues in ancient rocks allows us to find out the sunlight received at the time those rocks were on the surface, and this makes it possible to calculate the positions of the Moon and other stars with respect to the Earth at a given time.
In collaboration with Alberto Malinverno, geophysicist at Columbia University (United States), Meyers developed a mathematical tool to determine changes in the direction of the Earth’s axis and the planet’s orbit as a function of variations in the geological record, even for very distant times , although with greater uncertainty as they went back further in time.
This is how he managed to determine the length of the day 1,400 million years ago and the distance between the Moon and the Earth then. As both bodies move slowly but steadily away, Earth days get longer, albeit imperceptibly to our senses.
