Early Earth and the Origins of Life Why

Early Earth and the Origins of Life Why do we care?

Early Earth and the Origins of Life August 25, 2009 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 4567. 2± 0. 6 million years old

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

The Archean Earth System • Archean: 4. 03 to 2. 5 Ga • Late Heavy Bombardment (4. 1 to 3. 8 Ga) • Atmosphere: hardly any molecular oxygen (O 2); appears at ~2 Ga • UV radiation (no ozone shield) • Sun less luminous (20 -30%) • Length of day ~15 hours (~584 days per year) • 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 • Magnetic field by 3. 2 Ga w/ thanks to Stanley M. Awramik, 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 CO 2 (in addition to CH 4) 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 -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 Mc. Namara, 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. 85 Ga rock apatite (Ca-PO 4) grain in rock Nature, 1996 “carbonaceous” remnant material after apatite dissolved with acid And the controversy continues….

A primer for Schopf et al. , 2002 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)

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 (X-CO 3) -most commonly Ca. CO 3, the mineral in limestone -many marine organisms form carbonate shells (corals, foraminifera) limestone cliffs

C 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” -photosynthesis causes a very large shift in the relative abundance of 13 C and 12 C such that 12 C is preferentially incorporated into biological materials cross-section of a leaf

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