“Days lasted 19 hours in Earth’s distant past”| Daily list

A new study based on cyclostratigraphy has found that in Earth’s billion-year history, our days lasted just 19 hours.

It is a geological method that uses rhythmic layers of sediment To detect “Milankovitch” astronomical cycles that reflect how changes in Earth’s orbit and rotation affect climate.

The moon was nearer and the day was shorter. “Over time, the Moon has stolen Earth’s rotational energy from Earth to propel it into a higher orbit,” said Ross Mitchell, a geophysicist at the Chinese Academy of Sciences’ Institute of Geography and Geophysics and lead author of the newly published study. in Natural Geosciences.

“Most models of the Earth’s cycle show that the length of the day gets shorter and shorter over time,” said Uwe Kirscher, co-author of the study and now a researcher at Curtin University in Australia.

But not what Mitchell and Kirscher found.

How did researchers measure the length of the ancient day? In past decades, geologists used special sedimentary rock records that preserved very fine-scale layers of tidal marshes. Count the number of sediment layers per month caused by tidal fluctuations and you will know how many hours there are in an ancient day.

But such wave records are rare, and those that survive are often disputed. The new research is based on cyclostratigraphy.

“The two Milankovitch rotations, forward and tilt, correspond to the wobble and tilt of the Earth’s axis of rotation in space. Thus, early Earth’s rapid rotation can be traced to shorter cycles. Forward and tilt in the past.” explained study co-author Uwe Kirscher, who is now a researcher at Curtin University.

Mitchell and Kirscher Milankovitch took advantage of the recent proliferation of records, with more than half of the paleontology data generated in the past seven years.

“We realized it was time to try some kind of marginal, but completely reasonable alternative idea of ​​Earth’s paleorotation,” Mitchell said.

That is an unproven theory Day length may have been stuck at a fixed value in Earth’s distant past. In addition to ocean tides associated with the pull of the moon, there are also solar tides on Earth associated with the heating of the atmosphere during the day.

Solar atmospheric tides are not as strong as lunar ocean tides, but this has not always been the case. In the past, when Earth was spinning faster, the Moon’s pull would have been much weaker. Unlike the Moon’s pull, the Sun’s tide pushes the Earth. So while the Moon slows down the Earth’s rotation, the Sun speeds it up.

“Because of this, if these two opposing forces were equal to each other in the past, such a tidal oscillation would stop the length of the Earth’s day from changing and remain constant for a while,” Kirscher said.

That’s what the new data set showed.

Earth’s day length appears to have stopped its long-term increase Stabilized in about 19 hours between two and a billion years ago: “Billion years,” Mitchell noted, “are commonly called ‘boring’ billions, where Earth’s evolution has not undergone major changes.

Interestingly, there is stagnation between the two large increases in oxygen. Timothy Lyons of the University of California, Riverside, who was not involved in the study, said: “It is very attractive to think that the evolution of Earth’s rotation may have influenced the evolution of the composition of the atmosphere.”

Thus, the new study supports the idea that photosynthetic bacteria must wait longer days to produce more oxygen each day for Earth’s modern oxygen levels.