The natural phenomenon responsible for the tides on Earth is the gravitational pull exerted by the moon and, to a lesser extent, the sun. These celestial bodies create tidal forces that cause the oceans to bulge, leading to high and low tides. The moon's gravitational influence is stronger due to its proximity to Earth, resulting in more pronounced tidal changes. Tides are cyclical and occur approximately every six hours, significantly impacting coastal ecosystems and human activities.