Linear conjugated molecules with alternating single and double bonds also will absorb light if they are long enough. Carotenoids, which are "super butadienes" with 22 carbon atoms connected by alternating single and double bonds, are used as antennae by green plants to trap light and transfer the energy to chlorophyll for use in chemical syntheses. They are bright yellow-orange because they have evolved over the past 3.5 billion years to absorb light in the 5000 Å wavelength region (blue-green), which is the most intense part of solar radiation. Living organisms use aromatic and straight-chain conjugated molecules to trap light energy, to transfer this energy from one molecule to another, and to recognize the presence of light so they can grow toward it, turn toward it, or use it for information gathering through vision. The radiation that reaches the surface of our planet covers a relatively narrow range. Ozone, O in the upper layers of the atmosphere absorbs almost all wavelengths shorter than 2900 Å, and water vapor absorbs much of the infrared. Little infrared radiation longer than 13,000 Å remains by the time light reaches the surface of the Earth, and only five meters below the surface of the ocean all radiation longer than 8000 Å has been absorbed. The most intense radiation from the sun occurs in the blue-green region, around 5000 Å, the region for which the carotenes have evolved to absorb light.