Answer:
A beneficial mutation that increased survival of certain plants that reproduced and passed the mutated gene to offspring.
Step-by-step explanation:
You may have heard that ultraviolet radiation is something extremely mutagenic, causing serious DNA damage and being one of the main initiators of cacinogenesis. This is true ultraviolet radiation can cause numerous mutations in the DNA, causing the appearance of numerous problems in the body.
However, in the question above we have an example of a mutation, caused by radiation, that had a beneficial effect on the organism and helped that organism to survive. This is because, in the question above, we can see that, in the first days of life on Earth, plants were exposed to extremely high doses of ultraviolet radiation. Constant exposure to UV has resulted in some terrestrial plants developing narrow leaves with thick, waxy cuticles. Over many, many generations, these narrow leaves have evolved into needles. We can say, then, that this was a beneficial mutation that increased the survival of certain plants that reproduced and transmitted the mutated gene to their offspring.