At first, the ultraviolet rays would be blocked by the global dust cloud that would blot out the sunlight and choke the planet in icy winter-like conditions for months. During the extended winter, animals across the biological spectrum would starve and become weaker, and many would die. The researchers calculated that the dust cloud would shield Earth from ultraviolet light for an extended period of about 390 days before the dust settled and the ultraviolet radiation returned to its level before the impact. After that, the ozone depletion would cause ultraviolet levels to at least double, about 600 days after 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 photosynthesis, which forms the base of the world's food chain. The researchers said that 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 ozone depletion would be less, but there would also be less of a protective dust cloud. During the K-T event, the scientists said, many of the animals may actually have been spared most of the ultraviolet spring they envision. That impact, oddly enough, hit a portion of Earth's crust that was rich in anhydride rocks.