Why Is Too Much Ultraviolet Radiation Harmful to Plants & Animals?

Most UV light is filtered by the ozone layer, but some escapes to the earth.

Ultraviolet (UV) radiation has a number of negative effects on life forms on earth. The paradox exists because of the wide spectrum of light emitted by the sun, and how plants use the energy that makes it through the atmosphere. For this reason, discussions of ultraviolet energy and damage often revolve around the ozone layer, which only lets in a fraction of the present UV light.

Light Radiation

All light is a form of radiation--to be specific, a form of electromagnetic radiation. Not all of it is intrinsically harmful, however. Light differs based on its wavelength, frequency, and energy. Human eyes can only see a relatively small band of the different light rays, a relatively harmless section that makes up all the colors our eyes can perceive and is produced often by synthetic sources like light bulbs. Higher energy light waves have a higher frequency and cannot be seen by humans, but also have more potential to damage organisms.

Ultraviolet Radiation

There are actually three different classifications of UV light--A, B, and C. UVA light passes through the ozone layer relatively unhindered and is the least harmful. UVB light is partially blocked by the ozone layer, but can damage lifeforms more easily. UVC light is very dangerous, but the ozone layer blocks almost all of it before it can reach the surface of the earth.

Burns

Burns are one of the most common types of damage resulting from exposure to UV light. UVC light can tan skin and burn surfaces like leaves most easily, since it impacts the surface layer that it hits directly, causing cells to break apart and blister. This radiant energy feels like heat for reason: its effects are very similar, and in high doses it can be very damaging for unprotected skin and delicate plants.

Genetic Damage

Genetic damage is more frequently caused by UVB, the stronger type of radiation. These light waves pass into the DNA in the cells of lifeforms and damage them. This would be catastrophic, but cells can repair most of the damage the light causes. However, the damage is still done, and sometimes it cannot be repaired or is repaired incorrectly. This causes sunburn damage, dying leaves, and eventually skin cancers.

Factors Affecting Damage

Both plants and animals have a wide variety of tolerance for UV light. Some plants, especially dark plants with thick leaves, can withstand more UV light than lighter, more delicate versions. Cloud cover and rain fall will also disperse much UV light before it can reach the ground.

References

• NASA: Ultraviolet Radiation
• The Ozone Hole: UV Rays
• Biospherical: Effects of UV Radiation on You