Which of the following is a primordial deity representing the earth?

Gaia is indeed the primordial deity representing the earth in Greek mythology. She is often referred to as "Mother Earth" and is one of the foundational figures in Greek cosmology. Gaia emerged at the dawn of creation, existing before the Olympian gods and embodying the very essence of the Earth itself. She is viewed as a nurturing figure who provides for all living things, reflecting her nature as the Earth.

Rhea, Themis, and Nyx, while significant deities in their own right, do not represent the earth in the same primordial sense. Rhea is known as the mother of the Olympian gods and is often associated with fertility and motherhood. Themis embodies divine order, law, and custom, primarily associated with justice and the oversight of social order rather than the physical earth itself. Nyx represents the night and is a personification of darkness, which is conceptually distinct from the earth as a sustaining entity. Thus, Gaia stands out as the primordial figure specifically associated with the earth in Greek mythology.