Earth Science And Geology Practice Exam

Tides arise from gravitational forces that external bodies exert on Earth's oceans, and the effect comes from the way gravity changes across the planet. The Moon and the Sun both tug on the oceans, creating bulges on the side of Earth facing them and on the opposite side as the pull weakens with distance. As Earth rotates, these bulges move, producing the regular rise and fall of sea level. The Moon has the stronger influence because it is much closer to Earth, so the gravitational gradient it creates is larger. The Sun, while far more massive, is so far away that its tidal effect is smaller, though still noticeable. When the Sun and Moon align, their tides reinforce each other, making higher high tides and lower low tides. When they’re at right angles, the tidal effects partially cancel, producing smaller tides. So the cause is the gravitational forces of the Moon and Sun, with the Moon contributing the largest portion of the tidal effect.