As inhabitants of Earth, our lives are affected by each of the four states of matter: solid, liquid, gas, and plasma. Most of the mass of the Earth is in the solid state. It provides a place for us to stand and it provides the gravitational field that keeps us as well as everything else bound to the planet, including the oceans (liquid), the atmosphere (gas), and the ionosphere (plasma). Our bodies need liquids and gases, especially water and oxygen. The gases of the atmosphere protect us from the most energetic of the photons from the Sun, those in the ultraviolet, the extreme-ultraviolet (EUV), and the x-ray regions of the solar spectrum.