Final answer:
It's harmful to have more UV radiation reach Earth because it damages DNA and skin cells, leading to skin cancer and cataracts. This increased radiation is a consequence of ozone layer depletion. Although UV radiation helps in vitamin D synthesis, the damaging effects on human health and ecosystems are significant.
Step-by-step explanation:
It is harmful to have more UV radiation reach Earth primarily because of reason C) Damages DNA and skin cells. Earth's ozone layer is crucial for protecting living organisms from the Sun's harmful ultraviolet (UV) radiation, especially UV-B which is known to cause direct DNA damage. DNA damage from UV radiation can lead to the formation of bonds between adjacent pyrimidine nucleotides, thymine, and cytosine, and this damage is a leading cause of skin cancer, including malignant melanoma, the most dangerous form. In addition, UV-B radiation contributes to the development of cataracts in the human eye.
While the ozone layer absorbs most of the UV-C and some UV-B light, reductions in stratospheric ozone levels have led to higher levels of UV-B reaching the Earth's surface, which poses a serious hazard to not only human health but also has ecological impacts such as reduced crop yields and damage to oceanic plankton populations.
Moreover, increasing UV radiation can also lead to the destruction of phytoplankton, key organisms at the base of the oceanic food chain, which would have severe consequences for the entire marine ecosystem. It is important to note, however, that while excessive UV radiation is damaging, UV light also plays useful biological roles, such as promoting the synthesis of vitamin D in human skin. Nonetheless, the adverse effects far outweigh the benefits when it comes to the increased UV exposure resulting from ozone depletion.