Most of Earth’s seas experience two high and two low tides each day. There is also a less noticeable tide in its solid crust, which causes a variation in height of about half a meter. The tides are caused by the combined effects of the gravitational pull of the moon and the sun. Clearly, the pull of lunar gravity is greatest where Earth’s surface is nearest the moon. On the opposite side of Earth, the pull of lunar gravity is weakest. The overall result is that there are equal-sized oceanic bulges on opposite sides of the planet.According to the passage, tides are caused by