Final answer:
Sunlight consists of about 95% UV-A and 5% UV-B radiation; with UV-A contributing to indirect DNA damage and UV-B being more effective at causing direct DNA damage and skin cancer.
Step-by-step explanation:
The percent of UV-A and UV-B that make up sunlight: Sunlight consists of solar UV radiation that is broadly subdivided into three regions: UV-A, UV-B, and UV-C, which vary in wavelength and, consequently, energy. The majority of solar UV radiation reaching Earth's surface is UV-A, accounting for about 95%. UV-A rays have a wavelength range between 320-400 nm and penetrate the deepest into the skin, contributing to indirect DNA damage that can lead to skin cancer. On the other hand, UV-B rays, which have a shorter wavelength range between 290-320 nm, make up a smaller fraction of the solar UV radiation due to the absorption of most UV-B and all UV-C radiation by ozone molecules in the upper atmosphere. As a result, UV-B comprises about 5% of the solar UV radiation that reaches the Earth's surface, but it still plays a significant role in skin damage as it is highly effective at causing direct DNA damage that can lead to skin cancer