Presently Earth makes a complete rotation every 24 hours. The Earth makes about 365 rotations each time it revolves around the sun. It is not known for sure why the Earth rotates at the rate it does but it is for certain that this rate of rotation is gradually slowing down. Not that we will notice it in our lifetime. It takes millions of years to notice any significant slowdown. The young Earth billions of years ago rotated much faster and a day lasted only several hours. Eventually the Earth's rotation will almost completely cease or the sun will have died out by then. The Earth's rate of rotation is gradually slowing due to the friction and tidal influences that gradually slow the Earth. When Earth formed the initial rotation likely developed as a storm of mass gelled and contracted. The rate of rotation may have been altered or increased when a giant body such as a smaller planet struck the Earth. One theory has the moon developing from the remnants of this great collision.

What would it be like if the Earth no longer rotated today? You may think that one side of the Earth would always be facing the sun while the other side of Earth would always be facing away. This actually would not happen since the Earth is still revolving around the sun. Suppose the United States side of Earth is facing the sun and Earth is not rotating but is still revolving around the sun. Now place the Earth on the other side of the sun. Once placed on the other side of the sun the United States would then face away from the sun. Thus, a year and a day would be the same if the Earth did not rotate. Locations on Earth would have 6 months of darkness and 6 months of light.

If Earth did not rotate it is unlikely Earth could support life as we know it. With such extremely long days the sunny side would have extremely hot temperatures while the shadow side would have extremely cold temperatures. All locations would experience extreme heat and extreme cold during the course of a year.