We are used to a day divided into day and night, with the sun rising in the east and setting in the west. But billions of years ago, a nascent Earth had only just begun to rotate. Why does our planet rotate, and what does it mean for us? Let’s find out.
The origin of rotation
In essence, our Earth is a giant cosmic spinner, set in motion about 4.5 billion years ago during the formation of the Solar System. One of the main theories is that as clouds of dust and gas collided in the universe, they began to contract and rotate, forming a protoplanetary disk. During this rotation, large parts of the disk began to condense, forming planets, including the Earth. This initial rotation has continued to the present day.
Another key theory to explain the Earth’s rapid rotation is the collision theory. According to this theory, in its early years the Earth collided with another cosmic body, perhaps the size of Mars, resulting in the formation of the Moon and a significant increase in the rate at which the Earth rotated on its axis. This collision gave the Earth the extra momentum we still see today.
Interesting facts about the Earth's rotation
Day length: Most of us are used to a 24-hour day. However, the actual time it takes the Earth to complete one complete revolution on its axis is about 23 hours and 56 minutes.
Precession: The Earth’s axis of rotation is not static. It slowly ‘wobbles’ due to the gravitational effects of the Moon and Sun, completing a full cycle in about 26,000 years.
The Earth’s shape: Because of its rotation, the Earth is not a perfect sphere. It is slightly flattened at the poles and expanded at the equator. This flattened shape is known as the geoid.
The rate of rotation is decreasing: Due to the gravitational interaction with the Moon, the Earth slowly loses its angular velocity. This causes the days to lengthen by 1.7 milliseconds per century.
Historical day length: According to some studies, a single day on Earth originally lasted only about 6 hours!
What if the Earth stopped spinning?
If the Earth suddenly stopped rotating (which, it should be noted, is impossible in practice), the consequences would be truly catastrophic. Firstly, the sudden cessation of rotation would trigger colossal tsunamis as the oceans, which continue to move due to inertia, would roll over the continents.
The atmosphere, also moving due to inertia, would have caused massive atmospheric disturbances. The wind speeds in these storms would have reached incredible levels, destroying everything in their path.
Without rotation, one side of the Earth would be constantly facing the sun. This would lead to extreme temperature conditions: continuous daylight would turn that side into a desert of incredible heat, while the dark side would be plunged into absolute darkness and terrible cold.
In addition, the lack of rotation would cause the Earth’s magnetic field to disappear or weaken significantly, since its maintenance is linked to the movement of the planet’s liquid inner core. This in turn would make our planet vulnerable to cosmic radiation and the solar wind.
The Earth’s rotation is a key determinant of many aspects of our lives and environment. It gives us the alternation of day and night, influences climate and weather phenomena, and the complex processes of the atmosphere and oceans. It is hard to overestimate the importance of this phenomenon. Although we have become accustomed to the constancy of this process, even the theoretical notion of what might happen if the rotation stopped makes us more grateful for our planet’s continuous dance through space.
Prepared by Mary Clair