UNIT 1.1
Origins and Evolution
of Life
Presented by:
Dr. David J. Des Marais
16
INTRODUCTION
UNIT 1.1
Origins and Evolution of Life
Dr. David J. Des Marais
Smithsonian Institution
Origins of Life: Approaches to the Problem
•
Divine Act: Has been revealed in the scriptures; lies beyond the
laws of science
•
Chance: Understandable within the laws of science, but a
product of several improbable, random events.
•
Deterministic Event: Lies within laws of science, thus
predictable and, in some cases, probable. “The origin of life can
be understood as a consequence of the evolution of the elements,
stars, solar systems and habitable planetary environments
H. Morowitz
17
INTRODUCTION
Four Approaches to Understanding the Origins of Life
ORIGIN OF SOLAR SYSTEMS,
PLANETS AND ENVIRONMENTS
REQUIRED FOR LIFE
CHEMICAL EVOLUTION
CHEMICAL SPECIES AND
MECHANISM LEADING TO
THE ORIGIN OF LIFE
PAST
ORIGIN
OF
LIFE
THE LIVING BIOCHEMICAL
RECORD OF EALY LIFE
BIOLOGICAL EVOLUTION
THE GEOLOGICAL
RECORD OF THE
EARLY BIOSPHERE
TIME
Probability of Life in the Universe
B = R* fp ne fl L
where:
B = Number of Biospheres
R* = Formation rate of stars suitable for life
fp
= Fraction of those stars with planetary systems
ne
= No. of planets per solar system suitable for life
fl
= Fraction of
L
= Lifetime of Biospheres
ne
where life actually appears
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PRESENT
INTRODUCTION
Life’s Basic Functions
Information
Storage and
Replication
Energy
Harvesting and
Transduction
Light
and/or
Reactants
Organic
Biosynthesis
Heat
CO2
and/or
Products
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Organic
Matter
INTRODUCTION
Continuity Principle:
For any postulated stage in biogenesis, there must be a continuous path
backward to the prebiotic state of the earth and forward to modern organisms.
H. Morowitz
Space
Sources of Organic Carbon on the Prebiotic Earth
UV catalysis
Atmosphere
IDP's, Comets
Meteorites
Shock Synthesis
Lightning
Land
Ocean
Photoreduction of Carbon
Hydrothermal Organic Synthesis?
Reduced
Inorganic
Species
Crust
D. Des Marais, 2003
20
Opportunities
to concentrate
chemical species
INTRODUCTION
Metabolism Recapitulates Biogenesis
Lipids (vesicles)
Metabolic intermediates
of C, H, O and P
Phosphorylated compounds
Keto acids
Reduced N and S
Amino acids
Nitrogen bases
C, H, N, O, P, S compounds
Cofactors
Macromolecules
Coding molecules
D. Deamer, U.C Santa Cruz
A. Pohorille
21
INTRODUCTION
Meteorite Impacts and the Origins of Life:
A Hypothetical Scenario
4.5
4.0
Billions of Years Before Present
BiosphereExtinguishing
Bolide
Cretaceous /
Tertiary Impact
Bolide
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3.5
Biosphere
Begins and
Develops
INTRODUCTION
Prebiotic
Era
Space
Anoxic &
Anaerobic
Era
Oxygenic
Photosynthesis
Era
Exo gen ous
Org anics
Atmosphere
H2
CH4
H2
CH4
Ocean
H2S
O2
H2
CO2
Fe2+
Crust
O2
H2
Abiotic
Organic H2S
Synthesis Fe2+CO2
Sedimentary
Organic C &
Carbonates
H
Anaerobic
H2S 2
Ecosystems
CO2
Fe2+
Sedimentary
Organic C &
Carbonates
23
Cyanobacteria
& Ecosystems
Sedimentary
Organic C &
Carbonates
INTRODUCTION
24
INTRODUCTION
Finding Pale Blue Dots:
Planetary vs Biospheric Signals
Region
accessible
by remote
sensing
Direct photodissociation
Stratosphere
Troposphere
Secondary chemical reactions
?
Biogenic emissions
Crust
Terrestrial biota
Aquatic biota
Abiotic
emissions
22 0 2 80
Temp.,
K
25
INTRODUCTION
Summary:
Origins of Life
•
•
•
•
Basic concepts of life
o Universal characteristics, defining life
o Thermodynamics and kinetics
Approaches to understanding life’s origins
o Framing the approach
o A divine act, a highly improbable event, or a deterministic process?
o Scientific approaches: Astronomy, organic chemistry, molecular biology, Earth
and planetary sciences
Environments suitable for life’s origins
o Drake equation: abundance and distribution in the cosmos
o Water and organic carbon compounds: the only options?
o Environmental niches and hazards on a young planet
Comprehending the process of emergence
o Continuity Principle
o Monomers to biopolymers
o Self-replicators (e.g., RNA) first versus cells/metabolism first
o Protocells
Early Evolution of Life
•
•
•
•
Why evolve?
o Evolutionary imperatives (drivers): competition for limited resources,
environmental change
o Natural selection of a diverse, reproducing population
The changing planetary environment
o Drivers of planetary change that are shared by all rocky planets
o Habitable environments: their nature and change over long timescales
Earth’s earliest biosphere
o Geological evidence of environments and ecosystems
o Biological evidence of microbial physiologies
Transition to a modern biosphere having multi-cellular life
o Bioenergetics: innovations are evolutionary drivers
o Atmospheric change: planetary versus biological effects
o The “biogeologic clock:” major evolutionary events and their timing
26
INTRODUCTION
Notes:
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