2097. Tree
Noah understood how something as strong as Heaven and Earth could decide to take that risky path. The destruction generated by the fusion of two different systems was incredible. It carried a type of power that both cultivators and worlds couldn't wield on their own.
The theory behind that might was quite simple. King Elbas had gotten his hands on a superior power by gaining access to the strongest type of energy in the cultivators' system. Something similar could happen when fusing fuels from two different systems, but the reaction would be far stronger in that case.
Of course, Noah also noticed the problems with that approach. He had Heaven and Earth as a living example of the drawbacks of that path. Yet, he had now seen with his own eyes what happened when fuels from two different systems had the chance to fuse without anything that controlled them.