Early Earth and the Origins of Life

Why do we care?

How old do you think Life is?

Early Earth and the Origins of LifeAugust 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: 4.5672±0.0006 Ga (billion years ago)

Linked solidification and cooling processes

Elkins-Tanton magma oceans at first…

Formation of the Moon: 4.53GaMoon 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. AwramikStanley M. Awramik, UCSB

Steps towards Life

1. synthesize biomolecules (organic C, amino acids)2. organize them into macromolecular systems3. 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 CO2 (in addition to CH4)

on the other hand…-meteorites contain appreciable amino acids

The Miller/Urey Experiment

A modern-day Miller/Urey experiment

Johnson et al., Science, 2008

-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

Jeff Bada, Scripps Inst. of Oceanography

What about combining the two? hydrothermal vents

“Hot volcanoe” and “cold soup” modelsregarding the origin of Life on Earth

Hazen, 2006

-organic molecules and aminoacids can be organized bymineral lattices as templates

Modified from Awramik and McNamara, in press

A schematic of evolution of life on Earth

Stromatolites:biofilms of cyanobacteriacapture 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 FossilsCandidates for Early Archean Fossils

Nature, 1996

3.85Ga rock apatite (Ca-PO4) grain in rock

“carbonaceous” remnantmaterial after apatitedissolved 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): 12C (99%) and 13C (1%)-for the most part, they behave identically-however, there is a slight difference in their “reactivity” (12C > 13C)-photosynthesis: 12C is preferentially incorporated into biological materials (low 13C 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 CO3)-most commonly CaCO3, 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