Origin of Life

How Did Life Evolve? 1) Spontaneous formation of macromolecules Require anaerobic conditions 2) cell membranes form 3) Replication involving DNA or RNA

Monomer Synthesis Can monomers form spontaneously? 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 catalysts: to make reactions happen faster

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 energy for chemical reactions so increase the rate of chemical reactions catalysts in the body = enzymes

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

Experiments by Sidney W. Fox and Sidney w. Fox and Aleksandr Oparin have demonstrated that protobionts form spontaneously. They formed liposomes and microspheres, which have membrane structure similar to the phospholipid bilayer found in cells may be formed spontaneously, in conditions similar to the environment thought to exist on an early Earth. These experiments formed

Are Protobionts Alive? No they can’t replicate themselves

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

Earliest Life Forms 3.9 bya prokaryotic anaerobic: live without O 2 fermenters: –use organic molecules for energy –waste products things like alcohol, lactic acid (not O 2 ) Chemoheterotrophs – chemical bonds as energy source carbon obtained by eating 3.4 byo, South Africa modern

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

Chemoautotrophic bacteria Fossils from 3.2 Billion years ago Near hydro-thermal vents Chemical bonds as energy source, obtain carbon from CO 2 = make own food

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

Anaerobic Photosynthesis light-absorbing pigments (like chlorophyll) probably already present Ring structures of chlorophyll form spontaneously from formaldehyde cyclic photosynthesis neither Requires nor produces free oxygen

First Cyanobacteria 3.5 bya some photosynthetic bacteria evolved to use H 2 O as an electron source 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

Ancient vs. Modern Cyanobacteria LivingPrecambrian

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

Aerobic Bacteria some bacteria evolved antioxidant mechanisms allowed those bacteria to tolerate rising O 2 levels by 1.8 bya some bacteria even evolved to use O 2… Aerobic respiration Back to chemoheterotrophs

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

Stromatolites dome-shaped, layered structures as old as 3.5 byo 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?

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