The physical systems of the earth include the lithosphere, the hydrosphere, the atmosphere and the biosphere.
The hydrosphere consists of the earth's water. Approximately 70% of the earth's surface is water. It is found in oceans, lakes, rivers ponds, ice and ground water.
The Lithosphere consists of the solid surface that covers the Earth. Features such as hills, mountains, plateaus, plains and ocean basins are land forms covering the lithosphere.
The atmosphere consists of the thin layer of gases that surround the earth and rises up to 100 miles from the earth's surface, beyond which is outer space.
The biosphere consists of all things living on the surface of the earth and includes animals and plants.
It will occur on December 21st.
How close the planet is to the sun and how much it is receiving the sun's radiation.
