What is matter? The atmosphere

The atmosphere is the Earth’s air shell; the word comes from Greek “atmos” (air) and “sphere” (ball). It protects the Earth from harmful radiation and from extreme heat and cold. The Moon, which has no atmosphere, is very hot by day and very cold by night, and its surface is covered with craters from falling rocks. Most small space rocks heading for Earth burn up in the atmosphere. The atmosphere has several layers. In the layer closest to the ground wind, clouds and rain form, and all life is here. Above it aeroplanes fly, higher still meteors burn up, and in the outermost layers satellites orbit. Air is a mixture of gases: about 78% nitrogen, 21% oxygen, and the rest carbon dioxide, argon, water vapour and other gases. The atmosphere is studied by meteorology: weather stations, weather balloons and satellites measure temperature, humidity and wind speed.