The ozone layer, a region within Earth’s stratosphere, acts as a natural shield, absorbing harmful ultraviolet (UV) radiation from the sun. Composed of ozone molecules, this protective barrier has been depleted by human-made chemicals. This depletion leads to increased UV radiation reaching Earth’s surface, directly correlating with a heightened risk of developing skin cancer.
The Ozone Layer’s Protective Role
The ozone layer is located approximately 15 to 35 kilometers above Earth’s surface within the stratosphere. Its primary function is absorbing a significant portion of the sun’s UV radiation, especially the most damaging types. This occurs as ozone molecules (O3) break apart into an oxygen molecule (O2) and a separate oxygen atom (O) upon absorbing UV-B radiation. These components then reform ozone, continuing the absorption cycle.
This absorption prevents harmful levels of UV radiation from reaching Earth’s surface, safeguarding all life forms. The ozone layer absorbed between 97% and 99% of incoming UV-B radiation. Without this natural “sunscreen,” higher levels of UV radiation would reach the surface, leading to detrimental effects on living organisms and ecosystems.
Understanding Ultraviolet Radiation
Ultraviolet (UV) radiation is a form of electromagnetic energy emitted by the sun, categorized into three primary types based on their wavelengths: UVA, UVB, and UVC. UVA radiation has the longest wavelength, ranging from 315 to 400 nanometers (nm), and is less effectively filtered by the atmosphere. Consequently, it accounts for approximately 95% of the UV radiation reaching Earth’s surface and can penetrate deeply into the dermis, the skin’s deeper layer.
UVB radiation, with wavelengths between 280 and 315 nm, is largely absorbed by the ozone layer, but some still reaches the Earth’s surface. This type of radiation is highly biologically active and primarily affects the superficial layers of the skin, causing sunburn and promoting skin aging and the development of skin cancer. UVC radiation, with the shortest and most energetic wavelengths (100-280 nm), is the most damaging type of UV radiation. However, it is almost entirely absorbed by the ozone layer and atmospheric gases like oxygen, preventing it from reaching the Earth’s surface.
A thinned ozone layer diminishes this protective filter, allowing increased levels of UVB radiation, and to a lesser extent UVA, to reach the planet’s surface. This increased exposure to UVB, which is highly effective at causing DNA damage, poses a direct threat to human health.
How UV Radiation Triggers Cellular Damage
Increased exposure to UV radiation, particularly UVB, directly damages skin cells through specific biological mechanisms. The primary impact of UVB radiation on DNA involves the formation of photoproducts, such as cyclobutane pyrimidine dimers (CPD). These form when adjacent pyrimidine bases in the DNA strand, like thymine or cytosine, bond together, creating a lesion that hinders normal DNA replication and transcription.
UV radiation can also lead to oxidative stress within cells. Light-excited molecules act as photosensitizers, forming reactive oxygen species (ROS). These ROS further damage DNA, leading to oxidized bases that disrupt cellular function. Such damage impairs the cell’s ability to repair itself and regulate growth, potentially leading to the accumulation of unrepaired lesions and subsequent mutations.
From Cellular Damage to Skin Cancer
The accumulation of unrepaired DNA damage, specifically from increased UV exposure due to ozone depletion, directly contributes to skin cancer development. When cells cannot properly repair cyclobutane pyrimidine dimers and other photoproducts, these lesions can lead to mutations in the cell’s genetic material. These mutations can affect genes like tumor suppressor genes and oncogenes, which normally regulate cell growth and division.
The uncontrolled growth and division of these mutated cells can lead to tumor formation. The most common types of skin cancer linked to UV radiation are basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and melanoma. BCC forms in the basal cells in the lower part of the epidermis, while SCC affects the middle and outer layers. Melanoma, the most serious type, originates in pigment-producing melanocytes and has a higher potential to spread.