How did life originate? Old hypothesis: “Organic soup” Old hypothesis: “Organic soup” Inorganic chemicals like methane, carbon dioxide and ammonia may have been present in Earth’s early atmosphere Inorganic chemicals like methane, carbon dioxide and ammonia may have been present in Earth’s early atmosphere Solar radiation, lightning, etc. triggered chemical reactions which formed amino acids – organic soup Solar radiation, lightning, etc. triggered chemical reactions which formed amino acids – organic soup Amino acids are the building blocks of proteins – the basic stuff of life Amino acids are the building blocks of proteins – the basic stuff of life

Miller – Urey Experiment No longer considered valid No longer considered valid No evidence that this was the early composition of the atmosphere No evidence that this was the early composition of the atmosphere Some evidence to suggest an oxygen- deficient, but otherwise modern atmosphere Some evidence to suggest an oxygen- deficient, but otherwise modern atmosphere

Possible Sites for the Origin of Life Tidal Pools Tidal Pools Clay Clay Pyrite Pyrite Bubbles Bubbles Hot springs/Hydrothermal Vents Hot springs/Hydrothermal Vents

Newer Idea Life may have originated near hot springs and volcanic vents Life may have originated near hot springs and volcanic vents Heat supplied the energy for life processes Heat supplied the energy for life processes Energy also available from chemical reactions Energy also available from chemical reactions

Organisms around a modern black smoker vent

Earliest Life: Prokaryotes Prokaryotes – cells with no nucleus Prokaryotes – cells with no nucleus Single cells Single cells Strings of cells Strings of cells Mats of cells - Stromatolites Mats of cells - Stromatolites

Earliest Life: Prokaryotes

Cyanobacteria – 3.46 Ga

Modern Stromatolites

Stromatolites

Extraterrestrial Origins of Life? Ingredients in comets Ingredients in comets Evidence from meteorites Evidence from meteorites Could life have been transplanted to Earth from an extraterrestrial source? Could life have been transplanted to Earth from an extraterrestrial source? Did life arise on Earth and other planets simultaneously? Did life arise on Earth and other planets simultaneously?

Magnetite from Martian Meteorite – evidence of bacteria?

The Allan Hills Meteorite Bacteria(?) from Mars

Life in Stasis: 3 Ga of Single Cells Life begins – approximately 4.0 Ga Life begins – approximately 4.0 Ga 3.8 Ga – first stromatolites 3.8 Ga – first stromatolites 3.46 Ga – filaments of cyanobacteria 3.46 Ga – filaments of cyanobacteria Ga – at least 12 species of prokaryotes Ga – at least 12 species of prokaryotes 1.0 Ga – first eukaryotes 1.0 Ga – first eukaryotes 0.9 Ga (900 Ma) – sexual reproduction 0.9 Ga (900 Ma) – sexual reproduction 600 Ma – first multicellular organisms 600 Ma – first multicellular organisms

The Ediacaran Biota Earliest Multicellular Life