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Most electromagnetic radiation is absorbed by the Earth’s atmosphere, including harmful X-rays, gamma rays, and ultraviolet light. Visible light is one of the most important categories not absorbed, allowing for organisms to develop sensory organs tuned to it. Radio waves easily pass through the atmosphere, allowing for radio technology and observatories.
The vast majority of electromagnetic radiation does not pass through the earth’s atmosphere. Humans should be thankful for that, as if it did, life as it is known would not exist. Harmful X-rays, gamma rays and ultraviolet light, mostly from the sun, are largely absorbed in the upper atmosphere. Much infrared radiation is also absorbed by carbon dioxide and water vapor in the atmosphere. If it weren’t, liquid water on the surface would be heated to boiling point and evaporate, leaving a dry Venus-like planet. Electromagnetic wavelengths longer than about 10 m (long wavelength radio waves) are absorbed in the blanket of charged particles surrounding the Earth, known as the ionosphere.
The most obvious category of wavelengths not absorbed by the atmosphere is visible light, with amplitudes between about 300 and 700 nm. Because these are one of the most important categories not absorbed by the atmosphere, because they are often generated by many common chemical reactions and for many other reasons, it is natural that organisms that evolved on the surface of the Earth have developed sensory organs well tuned to them it.
At electromagnetic wavelengths shorter than violet, ending at about 280 nm, atmospheric transmittance rapidly drops close to zero. Wavelengths longer than red, in the infrared portion of the spectrum, make it to some extent. They are also locally generated from anything that produces heat, and some organisms have evolved adaptations that allow for limited infrared vision.
Radio waves with wavelengths between about 5 cm and 10 m easily pass through the atmosphere. This is why these waves are probably the third most recognizable portion of the electromagnetic spectrum behind visible light and infrared. The transparency of the atmosphere to the waves allows for radio technology, as well as sophisticated radio observatories that provide researchers with information about the universe. Astronomical observatories aiming to obtain information on electromagnetic wavelengths blocked by the atmosphere must be floated on high-altitude balloons or placed on orbiting satellites.
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