The length of a day on Earth has not remained constant throughout its history. In fact, the length of a day has gradually increased over billions of years due to various factors, primarily tidal interactions between the Earth and the Moon.
The Moon's gravitational force exerts a tidal influence on Earth, causing a transfer of angular momentum between the two bodies. Over time, this transfer of angular momentum has led to a gradual slowing down of Earth's rotation. As angular momentum is conserved, the transfer of angular momentum to the Moon results in an increase in its orbital radius, causing the Moon to move farther away from Earth.
In the distant past, when Earth was in its early stages of formation, it had a much faster rotation rate than it does today. The interactions between the Earth and the Moon were more significant at that time, leading to more substantial changes in the length of a day. As the Earth's rotation slowed down due to tidal interactions, the length of a day increased.
However, it is important to note that the process of slowing down the Earth's rotation has not been constant. Various factors can influence the rate of change, including changes in the distribution of mass on Earth, such as the movement of continents and the melting of ice sheets, as well as interactions with other celestial bodies.
Currently, the length of a day on Earth is still gradually increasing, but at a very slow rate. The average increase is approximately 1.7 milliseconds per century. This change is minimal and has negligible effects on our daily lives, but it can be accurately measured using modern astronomical techniques.