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 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 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

evolution of life on Earth 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 To you, this may seem to be a messy slide;

259 benthos; 92 planters

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….