Ultraviolet Radiation on the Early Earth

What gave life the initial spark? Some mythical force that governs all or some natural reaction that was a product of the conditions of environment set in place by physics. There is still much debate, but our search is in a more academic environment. The evolution of the Sun could be an indicator to how the atmosphere has evolved to accommodate life. In the early era of the Earth we do know from other sources that there was no oxygen or ozone to help support life. What made life possible under such harsh conditions. The answer to this inquiry can be found by knowing the UV flux from the Sun during this time period.