The cause of tides on Earth is primarily the gravitational pull exerted by the moon and the sun on Earth's oceans. This gravitational force leads to the periodic rise and fall of sea levels, creating high and low tides. The alignment of the Earth, moon, and sun affects the magnitude of the tides, with spring tides occurring during full and new moons, resulting in higher tidal ranges, while neap tides, occurring during the first and third quarters, have lower tidal ranges.