During the extended winter, animals across the biological spectrum would become weaker, starved and more vulnerable. Many would die. Then comes ultraviolet spring, shining down on surviving plants and animals that have lost their resistance to ultraviolet radiation and penetrating more deeply, with greater intensity, into shallow waters than it ever has before. By our calculations, the dust cloud would shield the Earth from ultraviolet light for an extended period, with it taking about 390 days after impact before enough dust settled that there would be an ultraviolet level equal to before the impact. According to their study, these factors would lead to ultraviolet-related DNA damage about 1,000 times higher than normal, and general ultraviolet damage to plants about 500 times higher than normal.
Ultraviolet radiation can cause mutations, cancer, and cataracts.
It can kill plants or slow their growth, suppressing the photosynthesis which forms the base of the world's food chain. Smaller asteroid impacts, which have happened far more frequently in Earth's history, theoretically might cause similar or even worse problems with ultraviolet exposure, the researchers say. The ozone depletion would be less, but there would also be less of a protective dust cloud. Effects such as acid rain, fires, the dust clouds, cold temperatures, ozone depletion and ultraviolet radiation could all build upon each other. That impact, oddly enough, hit a portion of the Earth's crust that was rich in anhydrite rocks.