Water is the defining feature of the habitable Earth; it is essential for all life as we know it. Evolution and maintenance of life in extremely water limited environments, which cover significant portions of the Earth, is not well understood. Akin to life, water-driven processes leave unique marks on the Earth’s surface. Mars is the only other planet currently known to bear the marks of water-driven surface processes, albeit fossil and of great age. The slow biotic and abiotic surface processes that may operate even in the virtual absence of liquid water are still essentially unknown. What is evident is that transient episodes of increased water availability can leave long lasting traces in extremely water limited environments. Intriguingly, those traces of bursts in Earth surface evolution have rarely been related to bursts in biological colonization/evolution, and vice versa, although both relate to the same trigger: water.

The objective of this session is to showcase research on the mutual evolutionary relationships between Earth surface processes and biota in arid to hyper-arid systems, where both biota and Earth surface process are severely and predominantly limited by the availability of water (rather than by extreme temperatures).
Solicited topics include (not exhaustive):
• fingerprints of biological activity at the (water) limit of the habitable Earth
• surface processes operating in the (virtual) absence of liquid water on Earth or extraterrestrial analogues (e.g. Mars)
• thresholds for biological colonization and concurrent fluvial transformation of landscapes
• tipping point(s) of biotically and abiotically controlled Earth surface systems
• chronometric and spatial information on the colonization and radiation of biota
terrestrial climatic records of (hyper-) arid regions on Earth