Surprise! Earth had 19-hour day once, not 24!

A billion years ago, the Earth's day lasted only 19 hours!

Earth’s ancient day length discovered. (Pixabay)

In a shocking discovery, it has.been revealed that billions of years ago, the Earth's day length was shortened to around 19 hours. As shocking as it seems, the science behind the theory is even more intriguing. Earlier, day length was shorter due to the Moon being closer to the Earth. “Over time, the Moon has stolen Earth's rotational energy to boost it into a higher orbit farther from Earth,” said Ross Mitchell, a geophysicist at the Institute of Geology and Geophysics of the Chinese Academy of Sciences and lead author of a new study published in Nature Geoscience.

But, the question that arises, is how researchers could measure ancient day length? Decades ago, geologists used sedimentary rocks that were specially preserved with very fine-scale layering in tidal mud flats. The methods involved assessing the quantity of sedimentary layers formed each month due to tidal fluctuations. Yet, these valuable tidal records are uncommon and often subjected to conflicting interpretations.

Luckily, scientists found an alternative means to study the length of a day.

Geologists started using the Cyclostratigraphy method which uses rhythmic sedimentary layering to detect astronomical “Milankovitch” cycles and show the changes in the Earth's orbit and rotation.

The study shows that though the length of a day may have remained constant, the lunar tides and the solar tides were the reason for Earth to rotate faster in those times. But, the pull of the Moon slows down Earth's rotation, whereas the Sun's tide pushes it. If these opposing forces were to balance out, a tidal resonance could have resulted in a period of constant day length.

Earth's day length appears to have had flattened and plateaued at roughly 19 hours -- an era Mitchell referred to as "the boring billion." It stayed there for about a billion years.

And that also suggests, that going forward, humanity may well have to deal with a changing Earth day at some point in time.