Forces are constantly acting on the solar system. One way to think about how these forces affect life on Earth is to imagine what life would be like if things were different. For example, what would life on Earth be like if there was no moon?

The first thing that would be different are eclipses. They would be no more. No more solar eclipses, no more lunar eclipses. In fact there would be no more solar eclipses anywhere in the solar system. The earth is the only planet where, from the surface of the planet, one of the planet’s moons seems exactly the same size as the Sun and can just cover it, causing an eclipse.

The moon creates tides. If there was no moon the tides would be smaller because only the Sun's gravity would be affecting the planet. Since the moon is 400 times closer than the Sun, the tides would be much smaller.

The moon also acts as brake for the Earth's rotation. Without the moon, a day would only be eight hours. While that might be disorienting for people on Earth, the faster rotation would cause heavy winds (over 100 miles per hour) regularly.

Source
http://365daysofastronomy.org/2009/03/28/march-28th/ (CC BY-NC-SA)