Complex sentence: However, there is no direct evidence of ancient genetic systems, as recovery of DNA from most fossils is impossible because DNA survives in the environment for less than one million years, and slowly degrades into short fragments in solution.
Split into simpler sentences: However, there is no direct evidence of ancient genetic systems, as recovery of DNA from most fossils is impossible. This is because DNA survives in the environment for less than one million years, and slowly degrades into short fragments in solution.