Audio Guide：

Seawater on Earth is affected by the Sun and Moon’s gravity. This results in the flood and ebb currents. For instance, the Moon’s gravitational field may differ slightly for Earth’s seawater on the near and far side since at these two opposite locations the distances to the Moon are different. These variations lead to the rising and falling of seawater and form the tides. Also, due to Earth’s rotation, flood tide happens at an interval of 12 hours at the same location on Earth.