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.
2. For a planet where water covers 70 percent of the surface, Earth certainly makes its residents work hard for a drink. Aside from fish and other saltwater-sipping sea life, most of us have to share what little freshwater we can find on land. And that's no small task. Only 3 percent of all water on Earth is freshwater, more than two-thirds of which is locked up in glaciers and ice caps. Of the other third, barely a trickle collects on the surface â lakes, rivers, streams and swamps represent less than 0.5 percent of all freshwater worldwide.