Does the Silmarillion Contradict Third age History? How Powerful Were Those First age

[Eldy]

Originally Posted by R.R.J Tolkien

What do you have to offer in support the balrogs were not maia at this point? how did it kill gandalf and give him such trouble? is there something in the published text to suggest this? as far as i am aware tolkiens cosmology was finished and his understanding of balrogs as well.

The idea of Maiar did not yet exist at the time Tolkien wrote the encounter between Gandalf and Durin's Bane. The main text of LOTR was finished by 1949 (and the Moria material was first written much earlier), but the Maiar did not enter enter the picture until the 1950s during the reworking of the Annals of Valinor into the Annals of Aman. Morgoth's Ring discusses this in the chapter of that name.

The idea that Tolkien's cosmology -- or really anything else about the First Age -- was ever "finished" is a misconception and will impede any attempt to make sense of his writing. He obviously continued to tinker with the later Ages as well, but he tended to consider himself bound by published material except in the course of preparing new editions.