Carbon in Earth, a new publication by scientists collaborating on the Deep Carbon Observatory, notes that:
Among the gaps in our knowledge of deep carbon relate to the deep biosphere. Remarkable discoveries of subsurface microbial life and associated viruses hint at a surprising hidden diversity, primarily within the microbial domains of archaea and bacteria. [But] surprising discoveries of a rich subsurface community of eukayotes promises an even richer deep taxonomy. These findings, coupled with advances in single-cell genomics, predict a coming decade of extraordinary discovery.