1. Early Earth and the Origins of Life
Why do we care?
How old do you think Life is?

2. 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

3. The Geologic Timescale
LIFE
Life!?!

4. Planetary disk
with thanks to L. T. Elkins-Tanton, JPL
NASA/JPL

5. Ca-Al inclusions in carbonaceous chondrites: 4. 5672±0
Ca-Al inclusions in carbonaceous chondrites: ± Ga (billion years ago)

6. Linked solidification and cooling processes
Elkins-Tanton
magma oceans at first…

7. 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

8. 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

9. Steps towards Life 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

10. 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

11. 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

12. “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

13. evolution of life on Earth
A schematic of
evolution of life on Earth
Modified from Awramik and McNamara, in press

14. Stromatolites: biofilms of cyanobacteria capture and bind sediment
Pre-Cambrian?
Today, at Shark’s Bay,
Australia

15. 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., Nature, 434, p. 155):
Tyler
& Barghoorn,
Science,
1954 .

16. Candidates for Early Archean Fossils
To you, this may seem to be a messy slide;

17. 259 benthos; 92 planters

19. And the controversy continues….
3.85Ga rock
apatite (Ca-PO4) grain in rock
Nature, 1996
“carbonaceous” remnant
material after apatite
dissolved with acid
And the controversy continues….