Earth is the third planet from the sun. The volume of the earth is 1. Its density is 5.52 times the density of water. Its mass is 1. The earth is the only known planet in our solar system with liquid water on its surface. Over ¾ of our planet is covered by water. The earth’s atmosphere protects its surface like a blanket from the intense heat of the sun on one side and the coldness of space on the other. If it were much colder, all the water would turn to ice. If it were much hotter, all the water would boil away. Earth is the only planet where the temperature is just right for liquid water. Earth is covered with mountains, volcanoes, lakes, rivers, and oceans. Most of the surface material is made of rocks — high in silica, iron, and magnesium.