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Early Earth and the Origins of Life
Why do we care?
How old do you think Life is?
Early Earth and the Origins of Life
Lecture overview:
-formation of the solar system and Earth
-conditions on early Earth
-theories concerning the origin of life on Earth
-geologic evidence for earliest life on Earth
The Geologic Timescale
LIFE
Life!?!
Planetary disk
with thanks to L. T. Elkins-Tanton, JPL
NASA/JPL
Ca-Al inclusions in carbonaceous chondrites:
4.5672±0.0006 Ga (billion years ago)
Linked solidification and cooling
processes
Elkins-Tanton
magma oceans at first…
Formation of the Moon: 4.53Ga
Moon forms from debris of a collision between a Mars-sized body and Earth
Animation of moon formation, courtesy of Joe Tucciarone
The Archean Earth System
Archean: 4.03 to 2.5 Ga (Ga=billion years ago)
• Late Heavy Bombardment (4.1 to 3.8 Ga)
• Atmosphere: hardly any molecular oxygen (O2); appears at
~2Ga  earliest life probably anearobic!
• UV radiation (no ozone shield)  earliest life probably
underwater!
• CO2 and CH4 -rich atmosphere
• Likely warm surface conditions (80o to 45oC)
• High rate of heat transfer from core to surface, possible thin
crust, plate tectonics just being established
w/ thanks to Stanley M. Awramik, UCSB
Steps towards Life
1.
2.
3.
4.
synthesize biomolecules (organic C, amino acids)
organize them into macromolecular systems
emergence of self-replicating codes of molecules (RNA)
emergence of molecular evolution via natural selection
after Hazen, 2006
The Miller/Urey Experiment
Stanley Miller and Harold Urey (1953)
-ran experiment for one week
-observed 10% of C in organic form
-2% of C in amino acid form
but:
-too high-energy environment
(lightning not continuous)
-early Earth contained appreciable
CO2 (in addition to CH4)
on the other hand…
-meteorites contain appreciable
amino acids
A modern-day Miller/Urey experiment
Jeff Bada, Scripps Inst. of Oceanography
-redid the Miller/Urey experiment in 2007
-found 22 amino acids (more than M/U!)
-also analyzed the original M/U vials
using modern-day analytical techniques
Johnson et al., Science, 2008
“Hot volcanoe” and “cold soup” models
regarding the origin of Life on Earth
-organic molecules and amino
acids can be organized by
mineral lattices as templates
Hazen, 2006
What about combining the two?
hydrothermal vents
A schematic of
evolution of life on Earth
Modified from
Awramik and
McNamara, in
press
Stromatolites:
biofilms of cyanobacteria
capture and bind sediment
Pre-Cambrian?
Today, at Shark’s Bay,
Australia
An Opinion
• “…true consensus for life’s existence seems to be reached
only with the bacterial fossils of the 1.9-billion-year-old
Gunflint Formation…” Moorbath, S., 2005. Nature, 434, p.
155):
.
Tyler
& Barghoorn,
Science,
1954
Candidates for Early Archean Fossils
3.85Ga rock
apatite (Ca-PO4) grain in rock
Nature, 1996
“carbonaceous” remnant
material after apatite
dissolved with acid
And the controversy continues….