The Earth is secretly "slowing down", and a day may be extended to 25 hours in the future?

Tuchong Creative

Almost all celestial bodies in the universe are rotating, and the Earth is no exception. It is because of the Earth's rotation that we have day and night. But have you ever thought about this question: When we rotate on the ground, the speed will slowly slow down due to friction or other factors. Will the Earth rotating in space also slow down? Yes, and the Earth's rotation speed is decreasing step by step.

The reason why celestial bodies in the universe rotate is because there is relative motion between matter. The angular momentum generated will gather in the same direction if it is not completely offset, which forms the initial force of the celestial bodies' rotation.

In addition, the rotation of celestial bodies is also affected by other factors. This is also the reason why the earth's rotation is decelerating in steps. For example, tidal force, the dissipation effect of this force is opposite to the direction of the earth's rotation. Simply put, the gravity of the moon stretches the earth's water, causing tides to rise and fall. The tides rub against the coastline, consuming the earth's energy and causing the earth's rotation to slow down. Changes in the earth's interior may also have an impact. According to the principle of conservation of angular momentum, if the matter inside the earth is concentrated, its rotation speed must become faster. On the contrary, if a large amount of high-density matter in the mantle invades the shallow layer or erupts from the surface, the moment of inertia of the earth's rotation will increase, and its rotation speed will inevitably slow down.
Another example is global warming, which causes a large amount of melting of polar glaciers and changes the mass distribution of the Earth, and its rotation speed will also change accordingly, just like a spinning skater, when she opens her arms, her rotation speed will slow down.

In summary, although the impact of many factors may be relatively small, they will cause changes in the Earth's rotation speed on a long-term time scale.

Recently, Chinese scientists have discovered the step-by-step deceleration of the Earth's rotation over the past 700 million years through an interdisciplinary research method. They combined geological records with astronomical theoretical calculations, analyzed the "fossil clocks" of rotation rate changes in geological samples (such as ancient coral reefs, stromatolites, etc.), and measured the traces left by the periodic changes in the Earth's rotation preserved in these samples (such as sunstones and yearstones), and combined them with modern astronomical theoretical calculations to reveal that over the past hundreds of millions of years, the Earth's rotation speed has maintained a step-by-step evolutionary pattern of "deceleration-stabilization-deceleration-stabilization". Scientists also calculated that the main reason for the stagnation of the Earth's rotation deceleration between 500 million and 350 million years was the weakening of tidal dissipation caused by the continental-ocean structure at that time.

After uncovering the pattern of the Earth's rotation deceleration, scientists also calculated information such as the length of Earth's day in the past and the distance between the Earth and the Moon.
In the past 700 million to 200 million years ago, the distance between the Earth and the Moon increased by about 20,000 kilometers, and the length of the day increased by about 2.2 hours. In other words, 700 million years ago, a day was only about 20 hours; 200 million years ago, a day was extended to 23 hours.

By comparing biological evolution data, marine geochemical data, etc. of the same period, scientists also found that the two major deceleration periods of the Earth's rotation may have provided the necessary conditions for the evolution of early marine ecosystems.

The first one occurred 550 million years ago, just before the Cambrian explosion, which may be related to the sharp increase in biodiversity at that time. The second one occurred 250 million years ago. This period corresponds to the recovery of ecosystems after a large-scale biological extinction event. Changes in the Earth's rotation speed may have provided conditions for the adaptation and radiation of new life. At present, the most direct impact of the Earth's slowing down is the change in day length, and the corresponding changes in the duration and frequency of light. These will affect the weather and the diurnal temperature gradient, and then affect the climate, and then affect plant growth. These changes have prompted major adjustments in the biosphere, affecting the distribution, reproduction and extinction of species.

Obviously, the above results are of great significance.

First, it deepens our understanding of the geodynamic processes, especially the complex mechanism of the interaction between the Earth's rotation and internal and external factors. It also has important theoretical significance for reconstructing the evolutionary history of the Earth-Moon system and exploring the climate, environment, and biological evolution caused by the deceleration of the Earth's rotation.

Secondly, it provides an important time frame for biological evolution and environmental change on a geological time scale. In addition, it also has implications for understanding current and future trends in the Earth's environmental changes, such as how to assess the potential impact of human activities on small changes in the Earth's rotation. Finally, this study promotes interdisciplinary research in astronomy and geology and provides a reference model for exploring the rotation evolution of other planets in the universe.

Is the Earth still slowing down? The answer is yes.

According to the research results obtained by analyzing homologous earthquake data published in the journal Nature in 2024, the rotation speed of the inner core has gradually decreased since 2010. If this trend continues, the rotation speed of the earth's outer layer may also be affected due to the gravitational drag effect, thereby affecting the running speed of the planet Earth.

This subtle change is not only related to high-precision scientific research, but is also likely to affect our daily lives. For example, the rotation of the earth causes the incident angle of sunlight on the earth's surface to change continuously, and changes in the rotation speed will affect the intensity of sunlight; the rotation of the earth will directly affect the formation of atmospheric circulation and monsoons, thereby affecting the climate system.
In addition, changes in the Earth's rotation speed will also affect changes in the human body's biological clock and work and rest patterns, the accuracy of the Global Positioning System (GPS), measurement and calibration in aerospace, communications and other fields, and even climate change. Therefore, the study of the Earth's rotation deceleration is not only an exploration of Earth science, but also a profound insight into the future lifestyle of mankind.

The impact of the slowing Earth's rotation sounds like it permeates every aspect of life, but we don't have to worry too much. After all, the time scale of the geological period is huge. In this ever-changing world, all we need is to embrace life, maintain keen observation and a positive attitude, and continue to pursue more profound science and explore the more distant deep space.

This article is a work supported by the Science Popularization China Creation Cultivation Program. Author: Dong Hanwen

Reviewer: Xiao Long, Professor of China University of Geosciences

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.