To What Extent Does Terrestrial Life ‘Follow The Water ’?

1. To What Extent Does Terrestrial Life ‘Follow The Water’? Eriita JonesSupervisor: Dr Charles Lineweaver Research School of Astronomy and Astrophysics, Australian National University

2. Contents • Motivation • Constructing the model • Model: Phase representation of Earth • Quantifying Earth’s biosphere • Applying the model to Mars

3. Concept

4. Concept

5. Constructing the model

6. 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 ~ 75 km 440 C

7. The terrestrial biosphere • Maximum temperature of life: 122 C (Kashefi & Lovley, 2003; Takaiet al., 2008) • Minimum temperature of active life: -20 C (Jungeet al., 2004) • Maximum depth/pressure of life: 5.2 km in crust; 1.5 x 103 bar (Szewzyk & Szewzyk, 1994)

8. The terrestrial biosphere Coldest possible terrestrial water (-89 oC)

9. Where are there liquid water environments that may not support life? 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. Only dormant life found at high altitudes. Thermal vents are being searched for life > 121 C. Several groups have suggestive evidence of life around 250 C. ? Have not been searched for life.

10. Where are there liquid water environments that may not support life? LOW ALTITUDE LIFE MAY BE RESTRICTED BY LITTLE AVAILABLE LIQUID WATER OR NUTRIENTS. LOW TEMPERATURE AS A LIMIT FOR LIFE IS POSSIBLE BUT UNLIKELY. AT LOW TEMPERATURES LIFE MAY INSTEAD BE LIMITED BY LOW WATER ACTIVITY. ? LIFE MAY BE LIMITED BY HIGH TEMPERATURES. NO EVIDENCE FOR A HIGH PRESSURE LIMIT TO LIFE

11. Quantifying the terrestrial biosphere~ volume of the Earth ~ Volume of Earth with active life(life 5.28km crust, 10.3km ocean) Depth life in volume of Earth with liquid water (liquid water 75km; life 5.3km crust; 10.3km ocean) Max. depth 122C in volume of Earth with liquid water (liquid water 75km; 122 C at 32km)

12. Constructing the Martian model

13. Potential Martian biosphere Conditions for terrestrial life reached in shallow subsurface, if liquid water is present. ~ 9 m ~ 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.

14. 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.

15. Thank you 

16. 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.

17. Quantifying the terrestrial biosphere~ maximum extent ~ Volume of Earth with liquid water (100 %) Volume of Earth(100 %) 250 oC (95 %) 122 oC (1.5 %) 250 oC (3 %) 122 oC (43 %)

18. Quantifying the terrestrial biosphere~ volume of liquid water ~ 12/20