How did life originate?How did life originate?

• Old hypothesis: “Organic soup”Old hypothesis: “Organic soup”• Inorganic chemicals like methane, carbon Inorganic chemicals like methane, carbon

dioxide and ammonia may have been dioxide and ammonia may have been present in Earth’s early atmospherepresent in Earth’s early atmosphere

• Solar radiation, lightning, etc. triggered Solar radiation, lightning, etc. triggered chemical reactions which formed amino chemical reactions which formed amino acids – organic soupacids – organic soup

• Amino acids are the building blocks of Amino acids are the building blocks of proteins – the basic stuff of lifeproteins – the basic stuff of life

Miller – Urey ExperimentMiller – Urey Experiment• No longer considered No longer considered

validvalid

• No evidence that this No evidence that this was the early was the early composition of the composition of the atmosphereatmosphere

• Some evidence to Some evidence to suggest an oxygen-suggest an oxygen-deficient, but deficient, but otherwise modern otherwise modern atmosphereatmosphere

Possible Sites for the Origin of Possible Sites for the Origin of LifeLife

• Tidal PoolsTidal Pools

• ClayClay

• PyritePyrite

• BubblesBubbles

• Hot springs/Hydrothermal VentsHot springs/Hydrothermal Vents

Newer IdeaNewer Idea

• Life may have originated near hot Life may have originated near hot springs and volcanic ventssprings and volcanic vents

• Heat supplied the energy for life Heat supplied the energy for life processesprocesses

• Energy also available from chemical Energy also available from chemical reactionsreactions

Organisms around a modern Organisms around a modern black smoker ventblack smoker vent

Earliest Life: ProkaryotesEarliest Life: Prokaryotes

• Prokaryotes – cells with no nucleusProkaryotes – cells with no nucleus

• Single cellsSingle cells

• Strings of cellsStrings of cells

• Mats of cells - StromatolitesMats of cells - Stromatolites

Earliest Life: ProkaryotesEarliest Life: Prokaryotes

Cyanobacteria – 3.46 GaCyanobacteria – 3.46 Ga

Modern StromatolitesModern Stromatolites

StromatoliteStromatolitess

Extraterrestrial Origins of Extraterrestrial Origins of Life?Life?

• Ingredients in cometsIngredients in comets

• Evidence from meteoritesEvidence from meteorites

• Could life have been transplanted to Could life have been transplanted to Earth from an extraterrestrial Earth from an extraterrestrial source?source?

• Did life arise on Earth and other Did life arise on Earth and other planets simultaneously?planets simultaneously?

Magnetite from Martian Magnetite from Martian Meteorite – evidence of Meteorite – evidence of bacteria?bacteria?

The Allan Hills MeteoriteThe Allan Hills MeteoriteBacteria(?) from MarsBacteria(?) from Mars

Life in Stasis: 3 Ga of Single Life in Stasis: 3 Ga of Single CellsCells• Life begins – approximately 4.0 GaLife begins – approximately 4.0 Ga

• 3.8 Ga – first stromatolites3.8 Ga – first stromatolites

• 3.46 Ga – filaments of cyanobacteria3.46 Ga – filaments of cyanobacteria

• 1.9-1.7 Ga – at least 12 species of 1.9-1.7 Ga – at least 12 species of prokaryotesprokaryotes

• 1.0 Ga – first eukaryotes1.0 Ga – first eukaryotes

• 0.9 Ga (900 Ma) – sexual 0.9 Ga (900 Ma) – sexual reproductionreproduction

• 600 Ma – first multicellular organisms600 Ma – first multicellular organisms

The Ediacaran BiotaThe Ediacaran BiotaEarliest Multicellular LifeEarliest Multicellular Life