The fact that the temperature on Earth is appropriate for human life, being between the freezing point and boiling point of water, isn't just due to the distant between the Earth's orbit and that of the Sun (The Greenhouse). It is also due to the atmosphere that surrounds it. Parts of Earth's atmosphere act as a shield, insulating it with just the right thickness to trap in sufficient solar energy to keep the average global temperature within a liveable range. This insulating layer is composed of a collection of atmospheric gases known as "greenhouse gases" because the gases trap heat, as do the glass walls of a greenhouse. The gases are mainly water vapor (H20), carbon dioxide CO2), methane (CH4) and nitrous oxide (N20). They all act as effective global insulators to keep the Earths temperature within a constant range.
The sun radiates tremendous amounts of energy into space across the whole spectrums of wavelengths, with most of it concentrated in the visible and near-visible ranges of the spectrum (The Greenhouse). Visible light with wavelengths between 400nm and 700nm makes up 43 percent of the total energy emitted by the sun. Shorter wavelengths make up about seven or 8 percent, and these are very important because of their high energy. Ultraviolet energy has very high energy and is capable of breaking stable biological molecules apart. It is also the wavelength which causes sunburns and skin cancers. The longer wavelengths making up the remaining energy emitted by the Sun, about 49 to 50 percent of its emissions, lie in the near infrared regions of the light spectrum, with wavelengths from 700nm to 1000nm. Next is the thermal infrared, with wavelengths between five and 20 microns, and far infrared beyond that. The various components of the Earth's atmosphere absorb ultraviolet and infrared radiation before it reaches the surface of the Earth, but visible light penetrates the atmosphere.
The visible light is ...