Beijing, China

The Earth started rotating at a dramatically slow speed twice in the last hundreds of millions of years and one of those times was when the biggest mass extinction took place, as per the latest study.

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The other time it slowed was when rapid expansion of life took place on the planet, which was called the Cambrian explosion, said the Chinese scientists-led team. 

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Even though the world appears to rotate at a constant speed, the exact timing can change and does not remain precisely 24 hours. 

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Why did the Earth's rotation slow down?

The changes in gravity happen because of variations in the distance between the Earth and the moon and are known to cause ocean tides, however, the friction between the surface of the Earth and the tides also leads to a slight deceleration in its rotation. 

At the same time, the momentum is transferred by the Earth to the moon, because of which it gradually moves outward.

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As per the study, the rotation of the Earth has decelerated because of this phenomenon in the past.

After analysing for two years, the team, headed by Ma Chao from the Institute of Sedimentary Geology at Chengdu University of Technology, concluded that there was an increase of 20,000 km between Earth and the moon between 700 million and 200 million years ago, because of which the length of the day increased by around 2.2 hours.

“Specifically, there are two intervals with pronounced Earth rotation deceleration: between 650 and 500 million years ago (Mya), and between 350 and 280 Mya, separated by a period of stalled deceleration from 500 to 350 Mya,” wrote the team in a paper which was published in the Proceedings of the National Academy of Sciences.

Watch: Earth slows down by 1.33 milliseconds

The first shift took place during the Cambrian explosion, when complex life forms diversified rapidly. The second deceleration happened around 250 million years ago and coincided with the “Great Dying”, which is also called the Permian-Triassic extinction event during which 90 per cent of life on Earth was wiped out.

According to the research, the volcanic activity along with changes in the climate, sea levels and salt levels led to the extinction. 

Ma said that changes in sea conditions were linked to the shift in the rotation of the Earth. “The two major ‘fast-slow’ deceleration periods may have provided the necessary conditions for the early evolution of marine ecosystems," he said while speaking to Science and Technology Daily.

(With inputs from agencies)