Smooth muscle, such as in the digestive system, is also controlled by the autonomic nervous system. Like heart muscle, it is not under our conscious control. The SNS is responsible for controlling voluntary body movements, such as movement of the arms and legs.
The oceans cover 71 percent of the Earth's surface and contain 97 percent of the Earth's water. Less than 1 percent of the Earth's water is fresh water, and 2-3 percent is contained in glaciers and ice caps. The oceans contain 99 percent of the living space on the planet. If the ocean's total salt content were dried, it would cover the continents to a depth of 5 feet.
Even though the planet is 71 percent water, the largest percentage of Earth's water is saltwater in the oceans and cannot be used for drinking. The table describes the main locations of water on Earth. Notice that about 98 percent of Earth's water is saltwater. The remaining 2 percent is freshwater, but the majority of that percentage is found in the polar ice caps and glaciers, which is not readily available to us.