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Terrestrial radiation is electromagnetic energy that originates in the Earth or its atmosphere. It creates background radiation that is always present, though it may fluctuate on the basis of location. This is not dangerous; some of it occurs at wavelengths that do not pose a threat to human health, while in other cases the amount present is so low that it does not pose a threat to human health. Instruments that measure radiation can differentiate between different sources and may return values for terrestrial radiation separated out from other sources for the benefit of researchers.
Numerous radioactive elements are present in rocks, air, and water, including radon, uranium, and thorium. They continually undergo radioactive decay and break down into smaller elements. All of these processes produce terrestrial radiation. In addition, thermal radiation is a part of the energy emitted by the Earth. The sun heats rocks and soil, which release trapped heat during the evening hours, and various geologic and molecular activities also produce heat.
Researchers who study radiation must establish a baseline of background radiation that is always present in order to identify new sources and understand their impact. Terrestrial radiation can depend on location and values, for many places on Earth are available to help scientists calculate baseline levels. With these levels in hand, scientists can see how activities like nuclear power generation impact radiation levels to determine their impact on human, plant, and animal life. This information can be important for setting science policy and developing safeguards to prevent radiation damage.
The level of terrestrial radiation has not always been constant. Levels fluctuated throughout the history of the Earth in response to a variety of factors. When the Earth was new, it had more radioactive elements present, but these broke down over time and no external sources replaced them. Researchers can determine historic terrestrial radiation levels with a variety of tools, including measuring existing levels and extrapolating, given information about the behavior of radioactive elements.
Some confusion can surround the concept of background radiation. The public associates radiation with harmful elements, when in fact there are many different forms of radiation and not all of them pose a threat to human health. When someone turns up a thermostat to warm up a room, for example, that person is relying on thermal radiation to increase the temperature. This radiation is not harmful, unless it reaches very high temperatures that the thermostat is usually designed to prevent.