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 August 26, 2011 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 NASA/JPL with thanks to L. T. Elkins-Tanton, JPL

Ca-Al inclusions in carbonaceous chondrites: ± 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 (O 2 ); appears at ~2Ga  earliest life probably anearobic! UV radiation (no ozone shield)  earliest life probably underwater! CO 2 and CH 4 -rich atmosphere Likely warm surface conditions (80 o to 45 o C) High rate of heat transfer from core to surface, possible thin crust, plate tectonics just being established Stanley M. Awramik w/ thanks to Stanley M. Awramik, UCSB

Steps towards Life 1.synthesize biomolecules (organic C, amino acids) 2.organize them into macromolecular systems 3.emergence of self-replicating codes of molecules (RNA) 4.emergence of molecular evolution via natural selection after Hazen, 2006

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 CO 2 (in addition to CH 4 ) on the other hand… -meteorites contain appreciable amino acids The Miller/Urey Experiment

A modern-day Miller/Urey experiment Johnson et al., Science, redid the Miller/Urey experiment in found 22 amino acids (more than M/U!) -also analyzed the original M/U vials using modern-day analytical techniques Jeff Bada, Scripps Inst. of Oceanography

What about combining the two? hydrothermal vents  “Hot volcanoe” and “cold soup” models regarding the origin of Life on Earth Hazen, organic molecules and amino acids can be organized by mineral lattices as templates

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

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

Candidates for Early Archean Fossils

Nature, Ga rock apatite (Ca-PO 4 ) grain in rock “carbonaceous” remnant material after apatite dissolved with acid And the controversy continues….

ion microprobe -instrument that focuses a beam of charged ions onto the surface of a sample -charged ions generate ions for mass spectrometric analysis (separation by mass) -in this case, used to look at different “isotopes” of carbon

Carbon isotopes -C has two stable isotopes (12 protons, different # neutrons): 12 C (99%) and 13 C (1%) -for the most part, they behave identically -however, there is a slight difference in their “reactivity” ( 12 C > 13 C) -photosynthesis: 12 C is preferentially incorporated into biological materials (low 13 C values) cross-section of a leaf Mojzsis, 1996

Raman spectroscopy -instrument detects extremely small changes in energy of light/laser/IR radiation -in Schopf 2002, a laser is used to excite the sample molecules into a higher energy state; they report “Raman shifts” that denote changes in laser wavelength -shifts denote presence of specific chemical bonds and their relative orientations

kerogen -concentrated, high-molecular-weight organic compounds occuring in sedimentary rocks -precursor to fossil fuels (formed upon heating of kerogen) an oil shale carbonate (containing CO 3 ) -most commonly CaCO 3, the mineral in limestone -many marine organisms form carbonate shells (corals, foraminifera) limestone cliffs

trichome -any small outgrowth or appendage on certain plants and algae trichomes on a cannabis plant chert -finely-grained, silica-rich, microcrystalline rock -is a product of high-T chemical alteration of rocks

greenschist -metamorphic rocks resulting from low-T, moderate pressure environments -typically somewhat green in color