Charles Hollins, age 10, of Atlanta, GA for his question”

 Is sea level the same all over the world?

Sea level is the surface of the oceans. In geography and map malting, sea level is used as a standard from which we measure height and depth. Mt. McKinley, highest peak in North America, is 20,300 feet above sea level. The Mariana Trench, deepest pit so far discovered in the floor of the ocean, is 35,630 feet below sea level. The altitude of a flying plane is also measured from sea level.

But, when we visit the sea side, we see that the level of the water is always changing. It goes up and down with the tides. All the seas are connected to form one world ocean and the surface of the ocean also rises and falls twice each day with the tides. What’s more, sea water piles up ahead of strong winds, The level of certain bays and small seas may be higher or lower than the ocean. For this reason, standard sea level must be an average. It is an average or mean level of the sea surface midway between high and low tide.