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.
How Much of the Earth is Covered with Water? About 70% of the earthâs surface is covered with water. Ninety-seven percent of the water on the earth is salt water. Salt water is filled with salt and other minerals, and humans cannot drink this water. Although the salt can be removed, it is a difficult and expensive process. Two percent of the water on earth is glacier ice at the North and South Poles.