Stromatolites, Biosignatures, and Astrobiological Implications

For millennia, humanity has looked to stars and wondered, “Are we alone in the universe?” Although this question was initially the purview of philosophers, now, with leaps in scientific and technological advances, we have changed the nature of this question from existential to empirical. Today, the question “Are we alone?” serves as a crux to the field of astrobiology. To search for life elsewhere in the universe, we must first understand how life originates and evolves on Earth but also how biology leaves behind residual signatures of its existence. To address these questions, many astrobiology researchers have targeted stromatolite-forming communities as model ecosystems to explore how microbe–mineral interactions, under a range of environmental conditions, can lead to the formation of biosignatures. Stromatolites are depositional structures formed by the activities and interactions of microbes and have a fossil record dating back billions of years. Due to their long evolutionary history and abundance on the modern Earth, research on the biological, chemical and geological processes of stromatolite formation have provided important insights into the field of astrobiology, including the diversity and preservation of biosignatures. In this chapter, we examine the range of biosignatures found in stromatolites and how these markers improve our understanding of the past, present, and future of life in the context of astrobiology. We also discuss whether stromatolite research can play a role in the future exploration of habitable worlds in our own solar system and beyond.