Scientists chart Earth's ancient rotation slowdown

A joint study of geological data by Chinese and foreign researchers has revealed that the Earth's rotation decelerated in a step-like pattern 700 million to 200 million years ago. Ma Chao, the corresponding author and a professor at the Chengdu University of Technology, said university geologists — along with a team led by French astronomer Jacques Laskar, and teams of geologists from Germany and Ireland — reconstructed the evolution of the Earth's rotational deceleration during the period from 700 million to 200 million years ago, based on new analysis of selected high-quality cyclic sedimentary records. "This time period has significant research value due to its relatively complete geological records and its involvement in major events of the Earth's evolution, including the Cambrian explosion of life around 540 million years ago, and the Permian-Triassic extinction event about 250 million years ago," Ma said. "Tidal dissipation had been the main driver for decelerating the Earth's rotation, before it slowed down to the point where a day lasted over 23 hours and 45 minutes," Ma said, noting that this occurred approximately 100 million years ago during the Cretaceous period, the era of the dinosaurs.