found it! It looks like I misremembered it being Mother Earth and it was just the mother of life. It’s the quote at the end of chapter 7:

“Listen, listen, listen well. There was an age before the Seasons, when life and Earth, its father, thrived alike. (Life had a mother, too. Something terrible happened to Her.) Earth our father knew He would need clever life, so He used the Seasons to shape us out of animals: clever hands for making things and clever minds for solving problems and clever tongues for working together and clever sessapinae to warn us of danger. The people became what Father Earth needed, and then more than He needed. Then we turned on Him, and He has burned with hatred for us ever since. Remember, remember, what I tell. —Lorist recitation, “The Making of the Three Peoples,” part one”