SpaceShipOne made history when it penetrated the Earth’s atmosphere and entered suborbital space on Monday.

The Earth’s atmosphere is made of thin layers of gases that surround the Earth. It insulates us from the extreme temperatures in space; and acts like a blanket keeping heat close to the planet. It also blocks us from much of the Sun’s incoming ultraviolet radiation. The troposphere is the lowest region in the Earth’s atmosphere. It extends from the Earth’s surface up to about 11 miles. This is where all weather takes place; air rises and falls.

Above the troposphere is the stratosphere, where air flow is mostly horizontal. The stratosphere begins at 11 miles high and and extends 31 miles above the earth’s surface. The ozone layer, a particularly reactive form of oxygen, critical for life on earth, exists in the upper stratosphere. This layer is primarily responsible for absorbing the ultraviolet radiation from the Sun. On top of the stratosphere is the mesosphere that begins from between 31 and 50 miles above the earth’s surface.

Temperatures start to drop quickly in the mesosphere as you ascend. Above that is the ionosphere starting at about 43-50 miles high and continues for about 400 miles. It contains many ions and free electrons or plasma. Sunlight hits atoms and tears away the electrons. The ionosphere is very thin, but it is responsible for absorbing the most photons from the Sun, and for reflecting radio waves, making long-distance radio communication possible.

The exosphere is the outermost layer of the Earth’s atmosphere and it extends from about 400 miles high to about 800 miles There atmospheric pressure is very low (the gas atoms are very widely spaced) and the temperature is very low.