Origin of Life

Archean Atmosphere Composition estimated based on: gases in meteorites composition of atmosphere of other planets likely carbon dioxide, water vapor, nitrogen, carbon monoxide, hydrogen sulphide, hydrogen chloride (CO 2, H 2 O, N 2, CO, H 2 S, HCl) What’s missing? Still present in modern atmosphere Rare in modern atmosphere

Archean Rain H 2 O + CO 2 = H 2 CO 3 (carbonic acid; weak) H 2 O + SO 2 = H 2 SO 3 (sulfurous acid; weak) H 2 O + SO 3 = H 2 SO 4 (sulfuric acid; strong) H 2 O + NOx = HNO 3 (nitric acid; strong) H 2 O + HCl = HCl (hydrochloric acid; strong)

Photochemical Dissociation During photochemical dissociation, ultraviolet radiation from the sun causes photochemical (light-induced) reactions to occur reactions converted Archean gases into those in modern atmosphere (still minus oxygen)

Outgassing volcanoes and hot springs common in Archean both emit: H 2 O vapor, CO 2, and N 2 (ingredients in the modern atmosphere) but only small amount of oxygen

Origin of the Oceans outgassing and photochemical dissociaton - both produce abundant water vapor water vapor condenses and falls as rain oceans accumulated quickly at first decreased in growth as volcanic activity slowed salts added over 3.9 billion years as material eroded from continents

WHEN Did Life Evolve? Earth was molten during Hadean cooled somewhat by 3.9 billion years ago water could remain liquid at the surface

oxygen breaks down organic molecules life must have evolved before oxygen abundant Archean sediment dark-colored = unoxidized oxidized (rusted) sediment appears about 2.2 billion years ago life must have evolved before 2.2 bya

WHEN Did Life Evolve? oldest (possible) life-forms ~3.5 billion years old life likely evolved between 3.9 and 3.5 billion years ago

Compounds Necessary for Life C, O, H, N relatively heavy elements all present on Earth because close to Sol oxygen, hydrogen and nitrogen are gases carbon often only element left in fossils carbonization

Monomers building blocks of life must form for life to evolve strings of amino acids = proteins how did monomers first form? Amino Acids

Monomer Synthesis Miller and Urey - created “Early Earth Apparatus” early Earth atmosphere in the top electrodes to produce “lightning” primordial pond in the bottom

Results: after a week, primordial pond became primordial soup 12 of 20 most common amino acids synthesized + other stuff next step: polymerization

Polymers chains of molecules proteins carbohydrates lipids nucleic acids

Requirements for Polymerization energy source: to drive reactions protection: from too much energy concentration: to bring materials together so they can react together catalysts: to make reactions happen faster and more efficiently

Energy Source Energy induces chemical reactions volcanoes lightening cosmic rays UV radiation

Protection too much energy can be a bad thing! early organic material protected by: rock ledges, under ice, under thin film of sediment, just under surface of water

Concentration concentration brings reactants together evaporation freezing clay

Concentration - clay clay forms particles called platelets platelets are: –very small –flat –with negative charge on surface

Clay organic molecules are attracted to clay surface concentrate and align Examples: bentonite (kitty litter, mud masks), kaolinite (Kaopectate)

Catalysts decrease amount of energy needed for chemical reactions so increase the rate of chemical reactions catalysts in the body = enzymes without enzymes, reactions in the body would be too slow to support life

Making Cells what is required to make a cell? DNA: passes on genetic code cell membrane: –protects the cell –homeostasis

phospholipids each molecule has a hydrophobic end and a hydrophilic end when surrounded by water, phospholipids form a sphere hydrophobic ends protected on the inside

Protobionts fatty acid spheres that form naturally polymers and enzymes concentrated inside reactions occur inside protobionts: –maintain their structure –increase in size over time –divide when too large –selectively absorb and release compounds –metabolize starch –store and release energy

Are Protobionts Alive? No they can’t replicate themselves

Replication process by which organisms make copies of themselves asexual reproduction sexual reproduction

Origin of Heredity many different types of protobionts those best able to accumulate organic molecules, grow, and divide become most common but “competition” is useless unless traits can be passed on/inherited polymers that can replicate themselves: DNA and RNA

Origin of Heredity short strands of RNA assemble naturally replicate themselves if more monomers available zinc, copper act as catalysts

Archaebacteria oldest living life forms likely similar to earliest life forms live in “extreme” environments extremophiles halophiles

Earliest Life Forms Likely: prokaryotic anaerobic: live without O 2 fermenters: –use organic molecules for energy –waste products things like alcohol, lactic acid (not O 2 ) source of organic molecules - primordial soup 3.4 byo, South Africa modern

The First Energy Crunch organic molecules floating in primordial soup become depleted competitive advantage goes to - organisms that can make their own food from inorganic molecules crisis solved for some by origin of _____________ fermenters resticted to limited environments Photosynthesis

Anaerobic Photosynthesis light-absorbing pigments (like chlorophyll) probably already present light provides energy to produce fuel from H 2 S S produced and released as a by-product 6CO 2 + 6H 2 S carbon dioxide hydrogen sulfide C 6 H 12 O 6 + 6S sugarsulphur energy from sunlight

First Cyanobacteria some photosynthetic bacteria evolved to use H 2 O instead of H 2 S light + H 2 O used to produce fuel O 2 released as a by-product problem: O 2 breaks bonds of organic molecules (i.e. - it’s toxic) 6CO 2 + 6H 2 O carbon dioxide water C 6 H 12 O 6 + 3O 2 sugaroxygen energy from sunlight

How Far Back Does the Fossil Record Extend?

3.5 byo - Australia Warrawoona Group, Australia Maybe? Modern cyanobacteria for comparison

byo - South Africa Fig Tree Group Likely

900 myo - Australia Bitter Springs Formation Almost Certainly

Bacterial fossils preserved in the act of division. modern bacteria in similar stages of division 2.1 Billion years old, Hudson Bay, Canada ~3.4 billion years old, South Africa

The Oxygen Revolution (Pollution) Indirect (non-fossil) evidence for the presence of cyanobacteria ~ 3.5 bya

Oxygen the modern atmosphere contains about 21% oxygen where did the oxygen come from? Oxygen Revolution Cyanobacteria - the first major global polluters

Ancient vs. Modern Cyanobacteria LivingPrecambrian

BIFs (Banded Iron Formations) thick (100s of feet) deposits consist of layers of iron-rich rock interbedded with iron-poor chert Precambrian, Australia

BIFs began forming about 3.5 bya reached peak about 2.5 bya deposition ended about 1.8 bya how did they form?

BIF Formation in the absence of oxygen, iron is easily dissolved in water with free oxygen in the water, iron bonds to oxygen and becomes a solid the solid sinks to the ocean floor and is deposited in layers

Why are BIFs Banded? oxygen likely produced by anaerobic bacteria living in a layer along the surface of the ocean oxygen was a byproduct of their photosynthesis oxygen is toxic to them but not if it is removed from their environment by bonding with iron

Why are BIFs Banded? at some point, all of the available iron may have bonded with the oxygen produced by photosynthesis oxygen would then build up and kill the anaerobic bacteria Some bacteria survive to rebuild population

Why are BIFs Banded?

Oxygen Crisis eventually, oxygen built up in oceans then outgassed from oceans into the atmosphere corrosive (oxic) atmosphere led to first major mass extinction anaerobic bacteria restricted to refuges without abundant oxygen (stagnant water, deep soils, etc.)

Red Beds sedimentary rocks that are very red form above the surface of the water iron minerals in the sediment “rust” indicate continuous presence of free oxygen in the atmosphere

Aerobic Bacteria some bacteria evolved antioxidant mechanisms allowed those bacteria to tolerate rising O 2 levels some bacteria even evolved to use O 2

Why Do We Care Again? build-up of free oxygen started ~ 3.5 bya argues for evolution of photosynthetic life by that time living organisms completely altered the face of the planet

Earliest (Undisputed) Evidence of Life - Stromatolites 2.2 byo Michigan

Stromatolites dome-shaped, layered structures may be as old as 3.5 byo became very abundant by 2.2 bya consist of layers of bacteria upper layers aerobic, photosynthetic lower layers anaerobic produce abundant oxygen how do we know?

They are still alive today in special environments, notably Shark Bay, Australia Tide In Tide Out

1 cm Formation of Stromatolites Cyanobacteria form a mat on top of sediment A new layer of sediment is deposited on top Bacteria grow up through new layer

Stromatolites provide evidence for the occurrence of cyanobacteria in the fossil record. Ancient Modern

if we use stromatolites to infer the presence of cyanobacteria we might expect to find fossils of bacteria-like organisms in them...

And we often find them... Gunflint Chert (~2.0 billion years old), Canada

How Does It All Add Up?

O 2 added O 2 in Atmos.

The rise of cyanobacteria and the building up of oxygen in the Earth’s atmosphere had three significant effects: 1.life forever changed the surface of the Earth 2.Earth experienced the first mass extinction 3.an oxygen-rich atmosphere set the stage for the appearance of complex life