For a billion years, a day on Earth lasted just 19 hours
Now we know why
The day on Earth did not always last 24 hours. A new study shows that it lasted only 19 hours and in fact this period lasted for a billion years, nicknamed the ” boring billion ” and was the result of a delicate balance of opposing forces, as the Moon was much closer to Earth and at a fixed distance .
Over time, the Moon “stole” Earth’s rotational energy to move into a higher orbit, further away from Earth.
The effect of this movement of the Moon was to slow down the rotation of the Earth and make the day a little longer. Previous research has shown that the day on our planet is getting longer at a rate of 0.000015 seconds per year and that the day has been increasing steadily for the last 3-4 billion years.
The new research took into account new geological data discovered in recent years. Statistical analysis for the Proterozoic Megaeon showed a stagnation in the length of the day between two and one billion years ago. In searching for the reasons for this relative stability, they found major changes in Earth’s atmospheric conditions, such as the Great Oxidation Event, where Earth’s oxygen levels rose and created the ozone layer.
Ozone absorbed more solar radiation than water vapor, enhancing solar tides when the atmosphere warms during the day. Solar tides are not as strong as ocean tides set by the gravitational interaction with the Moon. But when the Earth was spinning faster in the past, the Moon’s pull was less, about 1/4 of its current pull. And if the atmospheric tides were sped up by ozone and solar radiation, this may have been enough to maintain a delicate balance of opposing forces that led the Earth to a very long fixed period where the day lasted 19 hours.
Oceanic and atmospheric tidal forces had balanced each other, fixing the rate of rotation of the Earth to a fixed day length. The longer days provided enough light for photosynthetic bacteria to raise oxygen levels enough to support the Mesozoic Era, practically giving Earth the ability to develop complex life forms.
The research was published in Nature Geoscience .
