700 million years ago, there were no 24 hours in a day on Earth! ?

Author: Huang Xianghong Duan Yuechu

In the vast universe, the Earth is like a mysterious blue planet, constantly rotating and telling a long and wonderful evolutionary story. Have you ever thought that 700 million years ago, a day on Earth was only 20 hours? This amazing discovery has opened a door to the ancient history of the Earth.

The fact that the Earth's rotation speed is not constant has been fully confirmed in a recent study conducted by researchers Huang He and Professor Ma Chao from the Chengdu University of Technology's Big Data Sedimentation Research Team, in collaboration with international astronomer Jacques Lascar's team. Their research results reconstructed the process of the Earth's rotation slowing down from 700 million to 200 million years ago from geological records for the first time, and were published in the Proceedings of the National Academy of Sciences, which has attracted great attention.

Isn't a day 24 hours? The answer to this question is not as absolute as we think. In the long geological history, the rotation speed of the earth has undergone complex changes. The research team found that the rotation of the earth follows a step-by-step evolution pattern of "deceleration-stabilization-deceleration-stabilization". 700 million years ago, the time for the earth to rotate once was about 20 hours; and 200 million years ago, a day was 23 hours.

So how did these amazing discoveries come about? It turns out that the stones on Earth are the key to uncovering the secrets of Earth's history. The movement of the Earth affects the climate, and the information about climate change is recorded in the Earth's rocks in the form of physics and chemistry. In the eyes of scientists, the layers of sedimentary rocks sleeping under water are like a book of Earth's history. By "opening" this "book", one can "travel" back to the history of Earth's evolution.

Why does the Earth's rotation slow down? This is mainly related to the history of the Earth's evolution being affected by gravity. Among them, tidal dissipation is one of the main reasons for the Earth's rotation slowing down, which is related to the interaction between the Earth and the Moon. The Moon's gravity stretches the Earth's water, resulting in high and low tides. The tidal water rubs against the coastline, consuming the Earth's energy, thus slowing down the Earth's rotation.

Between 700 million and 200 million years ago, the two turning points of the Earth's rotation slowdown corresponded to two major geological events: the Cambrian explosion of life 550 million years ago and the Permian-Triassic mass extinction 250 million years ago. This discovery makes people wonder whether there is a causal relationship between these major events and the Earth's rotation slowdown? Although the specific causal relationship needs further verification, it undoubtedly provides new clues for our study of Earth history and life evolution.

700 million years ago, when the day lasted 20 hours, "carefree" single-celled organisms dominated the ocean. After the Cambrian explosion, complex life flourished, and the Anomalocaris, which was more than 2 meters long, dominated the ocean. During the mass extinction at the end of the Permian period, more than 90% of the world's species disappeared from the earth. However, the earth's creatures recovered and dinosaurs dominated the earth.

However, the main reason for the slowdown of the Earth's rotation does not seem to be static. In the 500 million years from the dominance of single-celled organisms to the appearance of dinosaurs, that is, from 700 million years ago to 200 million years ago, the distance between the Earth and the Moon increased by about 20,000 kilometers, and the Moon moved 4 meters away from the Earth every 100 years. The Moon's distance from the Earth gradually weakened the tidal dissipation effect. This study believes that the change in the distribution of the Earth's internal mass has become the main factor affecting the Earth's slowdown about 50 million years ago.

So what effects will the slowing down of the Earth's rotation bring? At present, the most direct impact of the slowing down of the Earth is the change in the length of the day and the corresponding change in the duration and frequency of light, which will affect the weather, and then the climate, and then affect plant growth. The specific change pattern needs further study.

It is worth noting that we are now in a stable period of Earth's deceleration, and there will be no turning period in the next million years. The time scale of the geological period is huge, usually measured in millions of years. Although we cannot personally experience the changes in the Earth's rotation speed in the long geological history, these research results have given us a deeper understanding of the Earth's past, present and future.

By studying the history of the Earth's rotation, we can not only better understand the Earth's evolution, but also provide important references for predicting future climate change and life development. The Earth, our home, still has countless mysteries waiting for us to explore. Let us look forward to more scientific discoveries and contribute to uncovering the mystery of the Earth.