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.
This finding can be used to show that back in time there was more water on Earth than today. (Photo:Colourbox) Although water covers 70 percent of the Earth's surface, water is actually a rare substance that represents just 0.05 percent of the Earth's total mass. Water has nevertheless played a crucial role in the emergence of life on Earth.