What are the two types of UV light that penetrate the atmosphere?

The correct answer is based on understanding the types of ultraviolet (UV) light and their interaction with the Earth's atmosphere. UV light is categorized into three primary types: UVA, UVB, and UVC, each with distinct characteristics and effects.

UVA rays have the longest wavelength (320-400 nm) and are known for penetrating the atmosphere effectively. These rays can reach the Earth's surface and contribute to skin aging and the risk of skin cancer. UVB rays, with a slightly shorter wavelength (280-320 nm), are partially absorbed by the atmosphere but still manage to reach the Earth's surface, playing a significant role in producing vitamin D in the skin and also causing sunburn.

In contrast, UVC rays (100-280 nm) are largely absorbed by the Earth's ozone layer and do not reach the surface under normal conditions. This is why UVC is not included in the answer. Understanding the role of UVA and UVB in both environmental exposure and their biological effects is crucial, which is why they are the correct pair that penetrates the atmosphere effectively.