"dark under the stars when it was fearless"?

[Lalaith]

Eldest, that’s what I am. Mark my words, my friends: Tom was here before the river and the trees; Tom remembers the first raindrop and the first acorn. He made paths before the Big People, and saw the little People arriving. He was here before the Kings and the graves and the Barrow-wights. When the Elves passed westward, Tom was here already, before the seas were bent. He knew the dark under the stars when it was fearless - before the Dark Lord came from Outside.’

The bold is mine. This part of the text has puzzled me for many years. Can anyone tell me, exactly when was the dark under the stars fearless? Did not Morgoth enter Arda as soon as it was made?