Relevance of the Avalon Assemblage as an Astrobiological Analog for Icy Ocean Worlds

We discuss the astrobiological potential of Earth’s first animals––the nearly 600-million-year-old Avalon assemblage––and the relevance that these ancient communities may have for the search for life on icy or cold water worlds. The Avalon assemblage originated on deep, dark, salty, and cold seafloors with intriguing similarities to hypothesized icy ocean world habitats. These fossils provide an opportunity to study the signatures of entire communities of organisms that lived under conditions unlike those on Earth today. We discuss how information gleaned from the Avalon assemblage applies to the search for life on icy ocean worlds and explore how the physicochemical nature of their habitat could provide insights for astrobiology search strategies. Although the focus in astrobiology is on microbial communities, complex macroscopic life modifies its environment in ways and at scales that microbes cannot. The Avalon assemblage allows investigation of the circumstances under which such life emerged, clarifying the role of stochastic and probabilistic processes in evolution. Avalonian communities and their paleoenvironments capture the ecosystems of a world in transition from microbe- to animal-dominated, illuminating the potential changes driven by these first animals—and their potentially detectable biosignatures. We close by framing questions that can leverage insights from the Avalon assemblage for biosignature detection and identify research opportunities for further exploration.