There are four oceans on earth that include the Pacific, Atlantic, Arctic and the Indian. According to NOAA scientists, the world’s oceans are responsible for covering 71 percent of the planet and represent 97 percent of the planet’s water supply. Oceans are not land-locked. They span from one continent to another. In contrast, lakes are surrounded by land. According to National Geographic Education there are millions of lakes on earth and they are found on every continent, in any environment, and at any elevation. Teachers and parents can use 3D maps of the world to engage students with the contrasting geographical features of the world's lakes and oceans.
Ocean water and lake water are like night and day. While most lakes are made of fresh water, the world’s oceans are high in salt. According to a U.S. Geological Survey Publication by Herbert Swenson, “if the salt in the sea could be removed and spread evenly over the Earth’s land surface it would form a layer more than 500 feet thick -- about the height of a 40-story building.” In contrast, fresh water has very small amounts of salt. Swenson continues to explain that when one cubic foot of sea water evaporates, it produces 2.2 pounds of salt while one cubic foot of water from Lake Michigan only produces one one-hundredth of a pound of salt. Instead, fresh water contains the same minerals found in the rocks and soil surrounding the lake.
Species of both lakes and oceans have evolved to be able to survive in their current conditions. If you were to take a lake trout and drop it into the Atlantic ocean, the salt would kill it. The main thing that separates freshwater fish from ocean fish is their salinity tolerance. Fish with very low tolerances to saltwater, like freshwater goldfish, are known as stenohaline species. These fish may survive in brackish water, where a stream meets an ocean and a low level of salt is present, but if the fish were to swim out to sea they would die. If teaching the theory of evolution is part of the curriculum, teaching the difference between freshwater and ocean fish may provide a gateway for introducing natural adaptation for survival.
When teaching the difference between lakes and the ocean, depth is an ideal topic to illustrate their vast differences. Oceans are almost always deeper. Located in the Western Pacific, the deepest part of the ocean is the San Marianas Trench at 11 kilometers (36,200 feet). The deepest lake in the world is Russia’s Lake Baikal. It’s deepest point is 5314 feet. Lake Baikal is truly a deep plunge, but it still doesn’t even reach half the depth of the ocean’s average depth at 14,000 feet. Teachers can get clear receptacles of water with various depths and use a little plastic toy man to illustrate ocean and lake depths in scale.