# Presentation: 180494

## Astrobiology and The Origin of Life on Earth- A Chemical Perspective -  

- Christopher Glein
- 2005 NASA Glenn Academy
- Mentor: Al Hepp
- Photovoltaics and Space Environments Branch

## Introduction 

- A multidisciplinary approach incorporating molecular biology, chemistry, ecology, planetary science, astronomy, information science, space exploration, and related disciplines.
- Asks three fundamental questions
- 	1. How does life begin and evolve?
- 	2. Does life exist elsewhere in the universe?
- 	3. What is the future of life on Earth and beyond?

- Astrobiology - the study of the origins, evolution, distribution, and future of life in the universe.

## Astrobiology is Not Science Fiction

## Goals of Astrobiology 

- Understand the nature and distribution of habitable environments in the universe
- Explore for past and present habitable environments in the solar system
- Understand how life originates
- Understand how past life on Earth interacted with its environment

## Goals of Astrobiology

- Understand evolutionary and environmental limits of life
- Understand the principles that will shape the future of life, both on Earth and beyond
- Determine how to recognize biosignatures on other worlds

## Project Goals

- Investigate possible life environments in the solar system
- Apply thermodynamics to planetary and biological systems to determine life potential
- Search for the beginnings of metabolism
- Establish the connection between metal sulfides and the origin of life on Earth
- Perform experiments using simple model reactive sites
- Hypothesize on cold organometallic chemistry on Titan

## What is life? 

- _Definition _
- A chemical system that
- undergoes Darwinian
- evolution and degrades
- high-quality energy from
- its environment in
- metabolism
- _Common Assumptions_
- Requires organic
- molecules and liquid water

## The First Living Entity

- The most popular hypothesis is that the first life form was a ribozyme – a catalytic RNA molecule
- It can mimic with limited functionality both DNA and proteins

## The Origin of Life 

- RNA molecules are complex molecules (contain 1000’s of atoms)
- Process: Build from simpler precursor molecules that gradually self-assembled
- Question: What molecules were present and how did synthesis occur?
- Consider two approaches
- 	- Thermodynamics
- 	- Experiments

## Thermodynamics

- The study of heat and energy and their relationship to material properties
- Define system of interest using state variables (pressure, temperature, composition)
- Quantitatively describe equilibrium directionality

**→**

**→**

**→**

**→**

- Systems

## The Solar System

- Where is there life?

## Extreme Earth

- Terrestrial organisms can thrive in many extreme conditions
- 	- temperature (386 K),
- 	- pressure (1300 bar)
- 	- radiation (1000 J m-2)
- 	- desiccation
- 	- salinity (5 M NaCl)
- 	- pH (0-10.5)
- 	- oxygen fugacity
- 	- heavy metals
- 	- organic solvents

## Venus

- Hothouse world
- Greenhouse effect from dense CO2-rich atmosphere
- Surface temperature ~735 K, Surface pressure ~92.1 bar
- Surface too hostile for life
- Clouds might have primitive life
- At 50 km, temperature ~350 K, pressure ~1 bar

- A disequilibrium atmosphere
- Sulfuric acid droplets with pH ~0

## Mars

- Frigid, desert-like environment
- Tenuous atmosphere of CO2, N2, and trace gases
- Surface temperature ~214 K, Surface pressure ~6.36 mbar
- Liquid water is not stable at the surface
- Large salt deposits found
- Possible hydrothermal life in subsurface water saturated with salts

## Europa

- A very cold place with no substantial atmosphere
- Surface temperature ~103 K
- An icy crust ~20 km thick covers a salty alkaline ocean (ionic strength ~0.3, pH ~10)
- Ocean depth ~100 km (Mariana trench ~11 km)
- Seafloor temperature ~260 K, pressure ~1.6 kbar
- Hydrothermal activity might support a viable biosphere

## Titan

- Icebox world
- Thick, mildly reducing atmosphere of N2, CH4, H2, and organics
- Surface temperature ~94 K, Surface pressure ~1.5 bar
- Rivers and lakes of liquid methane
- Possible subsurface ocean of H2O-NH3
- Natural laboratory for assessing prebiotic chemistry

## Other Possible Abodes of Life 

- Enceladus

- Triton

- Mercury

- Io

- Ganymede

## A More Quantitative Look at Planetary scale Thermodynamics 

| Planetary Body |  Chemical Potential Energy, ΔG  (J mol-1) |
| --- | --- |
| Venus | 1 |
| Earth  | 11,000 |
| Mars | 105 |
| Jupiter | 0.4 |
| Titan | 2 |

- ΔG = ΔG0 + RT lnQ

- Disequilibrium can be quantified using the Gibbs free energy
- Life creates disequilibrium by maintaining incompatible gases (i.e. CH4 and O2)
- Photosynthesis
-     CO2 + H2O  CH2O + O2
- Methanogenesis
-     CO2 + 4H2  CH4 + 2H2O
- Combustion
-     CH4 + 2O2  CO2 + 2H2O

## Entropy and Life

- microbe – open system of interest
- interior – irreversible chemical processes in cell
- Q – heat transfer
- matter – matter transfer
- dS(microbe) = dS(from exterior exchange) + dS(interior)
- dS(from exterior exchange) = dQ/T + dS(matter)
- dS(microbe) = dQ/T + dS(matter) + dS(interior)
- dS(microbe) = 0 (assume at steady state)
- -dS(interior) = dQ/T + dS(matter)

## Entropy and Life

- 2nd Law: The total entropy of the universe increases in spontaneous processes
- Exterior exchange helps cells stay in a state of low entropy at the expense of its surroundings.
- Life uses free energy from food to produce entropy and transfers it to the environment via heat (physical entropy) and metabolic byproducts (chemical entropy)

## Planetary Entropy

## Planetary Entropy

- Planets degrade low entropy solar energy to high entropy heat by physical and chemical processes
- Jupiter’s atmosphere is in a state of high chemical entropy and also has stable weather patterns
- Future Work: Connect physical entropy,  chemical entropy, and life.

## The Prebiotic World

- Iron-sulfur world hypothesis
- Life arose from reduced fluids reacting with metal sulfides
- Pyrite formation produces energy, ΔG0 = -38.4 kJ mol-1
- 	FeS + H2S → FeS2 + H2
- Energy used for metabolism (make complex molecules)

## Protometablism

- Citric Acid Cycle is widespread in nature
- Metabolism came from an older, simpler version
- Sulfur intermediates were used
- Metal sulfides catalyze the reactions
- Lattice structure resembles modern enzymes (iron-sulfur clusters)

## Future Literature Work in Metabolism

- Search for prebiotic catalysts used in primitive bacteria and archea
- Find important catalyzed metabolic reactions. Include reactants, products, and metal active sites
- Search for target intermediates in metabolism

## Future Experimental Work in Metabolism

- Perform experiments at Cleveland State University
- Synthesize important metabolic intermediate compounds
- Determine relevant physical properties
- Write a concise report of my results and conclusions

## Organometallic Chemistry on Titan

- Collaborating with Chris McKay at NASA Ames
- A poorly investigated area of study
- Cold organic solvent system (liquid methane)
- Erosion and weathering observed
- Start with theoretical solubilities
- What kind of chemistry is going on???

## Acknowledgements 

- Dr. Al Hepp
- Dr. Doug Ogrin
- Photovoltaics and Space Environments Branch
- 2005 NASA Glenn Academy
- Dr. M. David Kankam
- Office of University Programs
- Professor David Catling
- Dr. Chris McKay
- Washington NASA Space Grant
- Thank You!

## Questions