Earth is constantly bombarded by the sun’s radiation, also known as solar energy. The sun emits energy at wavelengths within the ultraviolet, visible, and infrared bands.
The Earth’s atmosphere is made up of gases namely, nitrogen, oxygen, argon, carbon dioxide, helium, hydrogen, methane, nitrous oxide, ozone, carbon monoxide, neon, krypton, xenon, iodine, ammonia, and water vapor. The properties, behavior and quantity of these gases vary, but collectively, they act like a blanket that protects and keeps the Earth warm enough to promote and support life.
On the Earth’s surface, here we find bodies of water such as oceans and lakes, land masses including volcanoes, and ice located at polar regions as well as snow on high altitude land areas and tepid latitudes. It is basically the habitable zone where all living creatures thrive, and the end receiver of solar energy.
Now, the sun’s light, heat and UV continually strikes the Earth, but the Earth somehow is able manage the amount of radiation via its ability to absorb and radiate said radiation, a process known as Greenhouse effect. How this works is analogous to how greenhouses stay warm for growing plants in parts where temperatures reach below zero, albeit through a different physical process.
When solar radiation enters the atmosphere, about a third that reaches the outer atmosphere immediately bounces off back to space. The remaining two-thirds of the solar energy is absorbed by the Earth’s surface and a portion of it by the atmosphere, and then the excess energy is radiate back out only at much longer wavelengths, generally in the infrared or thermal spectrum, since the Earth is much cooler than the sun. Ultraviolet and visible light are part of the electromagnetic spectrum, only UV radiation has shorter wavelength and a higher energy level than visible light.
While a portion escapes out to space, much of the infrared radiation is absorbed by the atmosphere. The gases within the atmosphere are able to hold and at the same time emit the energy in all directions, including back down to the surface, warming the planet. Without this cloak of gases, the average surface temperature would be lower than the freezing point of water. The Greenhouse Effect is how the planet achieves a certain radiative equilibrium essential to life.