Living organisms have been exposed to the damaging UV rays in sunlight ever since life began on the Earth, a little over 3.5 billion years ago. Indeed, UV levels on the early Earth's surface were significantly higher than they are now. UV light is absorbed by DNA and causes mutagenic and lethal damage, and today's life forms have evolved a range of strategies for surviving UV irradiation. These include protection from UV (e.g. by pigments, such as melanin, that absorb UV), repair of damaged DNA, and ways of surviving when the damage remains unrepaired (e.g. DNA polymerases that bypass DNA damage).

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