Monica M. GradyDepartment of Physical Sciences

Kensington & Chelsea Celebration of Science18th October 2014

The Chemistry of Life:and where to find it

Introduction

• Discovery of HT vent fauna in late 1970’s led to realisation that photosynthesis was not the only mechanism enabling the development of an ecosystem

• This has fuelled a search to find analogous sites beyond Earth:– Within the Solar System (satellites of other planets)– Beyond the Solar System (extrasolar planets and moons)

• Important parameters:– An appropriate energy source– A mechanism for converting energy into nutrients

Life Beyond Earth?

• Explore what we know about:– Life on Earth

• What is it?• How did it get here?• Where is it?

– Life beyond Earth• Within the Solar System• Beyond the Solar System

• Draw conclusions about the possible existence of life beyond Earth

Life on Earth• What is it?

“‘I’ll know it when I see it’ is not good enough”Carl Sagan, 1994

• So how is Life defined?– Growth, reproduction, locomotion, response,

excretion, respiration, nutrition

A Living Entity ?

A Non-Living Entity ?

Life on Earth

• ‘‘Life is a self-sustained chemical system capable of undergoing Darwinian evolution’’

G. F. Joyce, 1994–The ability to adapt and evolve

•Heredity: transfer of information

Conditions for life to arise

• Starting assumptions–laws of physics and chemistry not violated–Carbon-based

•What is so special about carbon?

Starting Materials

• Building blocks– (CO, CH4, NH3, H2O)–Role of comets

• Water• Substrate• Energy• Time• Stability

The Role of Comets• Dominantly ice • Rich in organic

compounds• Major contributor to

planetary bombardment– Delivered water and

organics to all planets– Potential for life

throughout Solar System

– Not PanspermiaNucleus of Halley’s comet (ESA)

Starting Materials

• Building blocks– (CO, CH4, NH3, H2O)–Role of comets

• Water• Substrate• Energy• Time• Stability

Water• Why is water important?

–Solvent–Support–Transport

Starting Materials

• Building blocks– (CO, CH4, NH3, H2O)–Role of comets

• Water• Substrate• Energy• Time• Stability

Stages in the Origin of Life

• Simple molecules (CO, CH4, NH3)• Complex molecules (RNA)• Template for self-replication• Membrane/boundary layer

Earth

• Has its good points– Liquid water– Magnetic Field– Atmosphere– Plate tectonics– Carbon cycle

Atmosphere & Magnetosphere

Energy Source for chemosynthesis on Earth

Hot rocks + seawater + redox reactions

Mars

• Rocky planet• Diameter about half that of

Earth• Are (or were) conditions

on Mars suitable for life to arise?– Nutrients supply?– Evidence for energy

source (heat)– Evidence for water

• Where might we find life on Mars?

Nutrient supply ?

• Mars formed from same source materials as Earth– Indigenous sources

• Mars bombarded by comets and asteroids– Endogenous sources

Mars: Water (far away)

Water (close-up)

Images from NASA

Microfossils in a martian meteorite?

D.S. McKay et al. (1996) Science

Ancient fossil life on Earth

• Microfossils’ in the Apex Chert, Western Australia (Schopf, 1983)

• Recent work has re-interpreted these structures as non-biological (Brasier group, Oxford)

• It will be challenging to detect life on Mars!

Where should we look for life on Mars?Below the surface, within rocks

1 cm

Europa• Second Galilean satellite• Very high albedo

• Covered in ice

• Magnetometer measurements imply sub-surface liquid• Not plate tectonics, but gravitational energy

Images: Copyright NASA

Same might also apply to Enceladus

Images: Copyright ESA/NASA

Ocean floorEuropan fauna ?

Images: NOOA/NOC/

Titan• Largest satellite of Saturn• Very thick atmosphere (N2, CH4)• Surface oceans (NH3, CH4, C2H6, )• Surface temp. -200°C, but can be raised during impact• Possible redox reaction: H2 + C2H2 CH4 ∆E ~ 334 kJmol-1 McKay & Smith, 2005• Compared with ∆E ~ 42 kJmol-1 for methanogens (Kral et al., 1999)

Images: Copyright ESA

Life beyond the Solar System

• Where to start looking?–Habitable zone

• What to look for?–Planet–Moon

Where to start looking ?

Habitable zone concept:UniverseGalacticPlanetary

Images: Copyright NASA-ESA-ESO

What to look for ?• Extra-solar planets

– ~ 1000 found so far– Mostly ‘hot Jupiters’

• Search for Earth-like planets orbiting solar-type stars• Search for Earth-like moons orbiting giant planets

Data from www.exoplanet.eu

Exoplanets and ExoMoons

Kipping et al. (2014) MNRAS (submitted)

Image: Copyright NASA

Now able to detect and characterise exoplanetary atmospheresMainly hot silicate dust, reducing

Search for an atmosphere

Would Earth have been recognised as a potential host of life ~ 2 byr ago?

• Methane (Swain et al., 2008. Nature 452, 329 – 331)• Water vapour (Tinetti et al. Nature 448, 169-171)

EvolutionSelection in a competitive environment• Starting point

– Physics, chemistry, ingredients• Environmental stress

– Atmosphere– Magnetic field– Tectonic structure

• Chance– Asteroid impact

Lead to different evolutionary pathways

Different Evolutionary Pathways ?

CH

NO

P

S

Evolution

Summary

• Have we found evidence for extant life beyond Earth?– No

• Have we found evidence for extinct life beyond Earth?– No

• Have we found evidence for habitats where life might exist beyond Earth?

–Yes