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To What Extent Does Terrestrial Life ‘Follow The Water’? Eriita Jones Supervisor: Dr Charles Lineweaver Research School of Astronomy and Astrophysics, Australian National University Contents •Motivation •Constructing the model •Model: Phase representation of Earth •Quantifying Earth’s biosphere •Applying the model to Mars Concept Concept Constructing the model Constructing the model Earth occupies 78 % of the phase space of liquid water. ~ 4 % of the volume of the Earth has liquid water 6380 km ~ 75 km 440 C 75 km The terrestrial biosphere Maximum temperature of life: 122 C (Kashefi & Lovley, 2003; Takai et al., 2008) Minimum temperature of active life: -20 C (Junge et al., 2004) Maximum depth/pressure of life: 5.2 km in crust; 1.5 x 103 bar (Szewzyk & Szewzyk, 1994) The terrestrial biosphere Coldest possible terrestrial water (-89 oC) Where are there liquid water environments that may not support life? Only dormant life found at high altitudes. Permafrost/ice core environments are being searched for life < -20 C. Terrestrial brines persist to at least – 30 C , thin films persist to -100 C. Unclear how much liquid is present at these temperatures. ? Have not been searched for life. Thermal vents are being searched for life > 121 C. Several groups have suggestive evidence of life around 250 C. Where are there liquid water environments that may not support life? LOW ALTITUDE LIFE MAY BE RESTRICTED BY LITTLE AVAILABLE LOW TEMPERATURE AS A LIQUID ORISNUTRIENTS. LIMITWATER FOR LIFE POSSIBLE BUT UNLIKELY. AT LOW TEMPERATURES LIFE MAY INSTEAD BE LIMITED BY LOW WATER ACTIVITY. ? NO EVIDENCE FOR A HIGH PRESSURE LIMIT TO LIFE LIFE MAY BE LIMITED BY HIGH TEMPERATURES. Quantifying the terrestrial biosphere ~ volume of theActive Earth ~ life (0.5 %) Volume of Earth with active life (life 5.28km crust, 10.3km ocean) Liquid water with life (12 %) Depth life in volume of Earth with liquid water (liquid water 75km; life 5.3km crust; 10.3km ocean) Liquid water too hot for life 122 C (57 % ) Max. depth 122C in volume of Earth with liquid water (liquid water 75km; 122 C at 32km) Volume of Earth (100 %) Constructing the Martian model Potential Martian biosphere ~9m Conditions for terrestrial life reached in shallow subsurface, if liquid water is present. ~ 10 m ~ 20 km Conditions for terrestrial life and liquid water between 10 m – 20 km beneath the surface. Ice likely present at these depths. Conclusions • Biosphere occupies < 1% of the volume of the Earth. Thus, after 4 billion years of evolution, the terrestrial biosphere has been unable to extend into ~99% of the volume of the Earth. • ~12% of the volume of the Earth where liquid water exists is known to host life. Thus, according to our current state of exploration, 88% of the volume of the Earth where liquid water exists, is not known to harbour life. • 65% of the phase space of terrestrial water and 88% of the volume of the Earth containing water, is not known to harbor life. Thus, we have shown that there are many liquid water environments on Earth that, as far as we know, do not host life. • The potential Martian biosphere must be between 10m – 20km beneath the surface, if liquid water is present. Coldest liquid water • Water activity below 0.6 thought to be a biological limit (Grant, 2004) •Thin films below –20 oC have a low activity & are only nanometres thick (Möhlmann, 2005; Jakosky et al., 2003) •Several common brines (eg. NaBr) have eutectics around -30 oC and activity above 0.6 • Candidate brines can provide a test of whether water activity or low temperature is a real limit for life. Quantifying the terrestrial biosphere ~ maximum extent ~ Volume of Earth (100 %) Volume of Earth with liquid water (100 %) 250 oC (95 %) 122 oC (1.5 %) 250 oC (3 %) 122 oC (43 %) Quantifying the terrestrial biosphere ~ volume of liquid water ~ Liquid water too hot for life (1.1 %) Liquid water with active life (< 98.9 %) Volume of liquid water (100 %) 12/20