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Abstract

Fluids containing ≥5% salt are classified as brines and exclude most life on Earth, but some microbes thrive at salt saturation (35% salt, 10 times the salinity of seawater). Recent findings of novel saline habitats such as subsurface aquifer seeps, deep-sea brine pools, and ancient subglacial brine (1–4) extend our knowledge on the limits of life on Earth and beyond (5) and elucidate how cycling of sulfur, methane, and iron can support microbial ecosystems in chemically isolated habitats in the absence of light (2).