Final answer:
An interglacial period likely led to an increase in biodiversity due to warmer temperatures and a stable climate favoring the development of diverse ecosystems, and the creation of new niches following glacial retreat that promoted speciation and species diversification.
Step-by-step explanation:
Entering an interglacial period resulted in an increase in biodiversity on Earth primarily because of two related factors. First, warmer temperatures and more stable climate conditions provided more favorable conditions for diverse ecosystems to thrive. This includes the melting of ice which exposed new land, offering fresh opportunities for colonization and diversification of species (D). Second, the retreat of glaciers and changes in the environment often created new niches, inviting rapid speciation and increased diversity. Additionally, the increased precipitation during interglacial periods might have created new habitats, fostering biodiversity (C). The overall more stable climate closer to the equator as well as the greater energy from the sun received in these regions, provided conditions that promoted biodiversity and allowed species to flourish.