life and extremes tori hoehler nasa-ames research center
Post on 19-Dec-2015
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Life and Extremes
Tori HoehlerNASA-Ames Research Center
Seeks to Understand the Origins, Evolution,
Distribution, and Destiny of Life in the Universe.
“Extremes”
Requirements and Limitations
What is Life?
In Astrobiology:
Think Globally, Act Locally . . .
Be practical about where to look and what to look for(that’s the only way to design discerning missions)
Think as broadly as possible about our key questions(or risk missing something important)
So what is life, anyway?So what is life, anyway?
Capable of Darwinian evolution (mutation and natural selection)
Some Commonly Cited Attributes:
Capable of reproducing itself
(Can carry out chemical reactions and synthesis)
(Can harness energy from the environment to drive these chemical processes)
So what is life, anyway?So what is life, anyway?Life According to Erwin Schrödinger (1944):
Does Something
Keeps on Doing Something (Longer than if it were Not Alive)
To keep doing that something requires plenty of energy
Doing anything requiring speed or specificity often requires molecules that are very complex
The Factory Analogy for Life
(cells are little factories that make more little factories)
To build a new factory, we require:
Raw Materials
Tools & MachineryEnergy & Work
A Blueprint
Energy,Life Requirements: Chemical Stuff,Conditions Appropriate for Complex Molecules, Solvent for Chemistry
Raw Materials
A way to connect the pieces together
A basic building block that can be assembled into large, complex backbones
Some interesting decorations to hang along the chain
(remember, we are talking about atomic materials)
A lesson from Earth . . .
Hydrogen(mostly filler)
Carbon(the backbone)
Sulfur, Oxygen(interesting decorations)
Phosphorus & Nitrogen
(backbone & decoration)
Chemical bonds are made from electrons, of which life requires some source
These building blocks are connected together by chemical bonds
This won’t happen (much) in the solid phase, because the molecules can’t come together across a significant distance. It could happen as a gas, but
complex molecules are so big that they usually break down before they vaporize. So the molecules
of life need to be dissolved in something.
For Earth life, water is the solvent
To do something, molecules need to interact
Energy
Chemical
Heat
Mechanical
(as visible light)Radiation
Bottom LineRequirements for (our) Life
Source of Carbon
Source of Electrons
Nutrients
Source of Energy Water
Microbiologists classify organisms based on how they fulfill these needs
What conditions threaten the integrity of big,
complex biomolecules?
Radiation
Strong Acid/Base
Harsh Chemicals
Heat
Any environment in which access to basic requirements is sketchy, or in which conditions threaten the stability of
biomolecules, could be considered extreme
How can we define the limits for life?
Some extremes are absolute (universal to life), some are relative (specific to a particular kind of life)
Use the only life we know – life on Earth – as a guide to understanding the prospects for, and how to seek, life elsewhere in
the universe.
How valid is the Earth-analog approach?
It’s the best we’ve got, so far . . .
Demands a focus on common traits, avoidance of highly specific circumstances
If we seek to broadly define life's capabilities and limits,
microbes are the place to look
GeneticDiversity
Aerobic (O2-based):
LightInorganic Chemicals
Organic Matter
Anaerobic:
LightInorganic Chemicals
Organic Matter
Microbial World
Microbial Mat
Macroscopic World
Plants
Animals
Metabolic Diversity
Tolerance of Extremes . . .
Acid Drainage (pH -0.7), Iron Mountain, CA(Photo: C. Alpers & D. Nordstrom, USGS)
Halite-Saturated Ponds, SF Bay(Photo: NASA)
Hydrothermal Vent (T = 115 ºC)(Photo: NOAA)
Some extremes that we will see
Low Temperature
Highly Salty
Chemical Toxicity
High Temperature
High / Low pH
Desiccation / High Radiation
Back to the Big Picture . . .
Understanding extremes on Earth, especially with the broad example of microbes, helps us to define “habitability”. In a theoretical sense, this tells us how common life could be. In a practical sense, it tells us where and how to
focus a search for life on other worlds.
Questions?