Rain is a liquid precipitation, in contrast to non-liquid precipitation such as snow, ice cubes and slit. Rain requires the presence of a thick layer of atmosphere to meet temperatures above the melting point of ice near and above the Earth's surface. On Earth, rain is the process of condensing water vapor in the atmosphere into water grains that are heavy enough to fall and usually arrive on land. Two processes that may occur together can push the air getting saturated before the rain, which is air cooling or adding moisture to the air. Virga is precipitation that falls to Earth but evaporates before it reaches the land; this is one way of saturation air. Precipitation is formed through a collision between water grains or ice crystals with clouds. Raindrops have a variety of sizes ranging from precise, like pancakes (large grains), to small balls (small grains).