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Early Earth
• 4.6 billion years ago (bya)
• Early atmosphere:– No free oxygen– Primarily nitrogen and
carbon dioxide– High energy from
lightning, UV radiation• Photo Credit: Mount St. Helens, May 18, 1980, taken by
Austin Post, USGS
Conditions of Early Earth
• Intense volcanic activity
• Meteorite bombardment
• Warm environment
• Photo Credit: Courtesy of NASA @ http://origins.jpl.nasa.gov/habitable-planets/images/ra7in16-early-earth.jpg
Earliest Evidence of Life
• Oldest fossil organisms: photosynthetic cyanobacteria
• Western Australia
• 3.5 bya
Fossil Stromatolites
• Multiple layers of cyanobacteria
• Secreted CaCO3
dome-shaped structures
• First reefs
Earliest Life
• Single-celled organisms probably evolved before 3.9 bya
• No 3.9 bya fossils• Photo Credit: Robert Simmon, 2008, NASA,
Wikimedia Commons
Jack Hills: Rock formation in Australia; rocks > 3.6 bya; 4.4 bya zircon crystal found in this formation
Why No 3.9 BYA Fossils?
• Few rocks date to 3.9 bya
• Tiny unicellular fossils are hard to find
• Photo Credit of Proterozoic Stromatolites: UNP, 2006, Wikimedia Commons
Molecular Fossils
• Chemical traces of biomolecules
• 3.9 bya evidence of prokaryotic lipids
• Photo Credit of Hopanoid Compound: MarcoTolo, 2006, Wikimedia Commons
Abiogenesis
• Origin of life from non-living components
• Photo of Stanley Miller: NASA, 1999, Wikimedia Commons
Four Steps of Abiogenesis
• Step 1: Synthesis of organic monomers from inorganic molecules
• Photo credit for amino acid, tryptophan: Boghog2, 2007, Wikimedia Commons
Four Steps of Abiogenesis
• Step 2: Organic Monomers Organic Polymers
• Catalysts?• Photo Credit for Kassinin: Edgar181,
2007, Wikimedia Commons
Four Steps of Abiogenesis
• Step 3: Protobionts form
• Protobiont = Organic molecules surrounded by membrane-like structure
Four Steps of Abiogenesis
• Step 4: Heredity• Pass instructions to
offspring• Controls protein
synthesis • 1st genetic material:
RNA?• Photo Credit of Hammerhead Ribozyme: William G.
Scott, 2007, Wikimedia Commons
Where did Abiogenesis Occur?
• Hypotheses:– Hydrothermal vents– Tide pools– Panspermia: from
outer space• Photo Credit for Black Smoker: NOAA, 2006,
Wikimedia Commons
Evolution of Prokaryotes?
Photo Credit of Lassen Volcanic National Park Hot Springs: Walter Siegmund, 2005, Wikimedia Commons
Oxygen Revolution
• Oxygen accumulated
• Most anaerobes died
• Some survived in anaerobic habitats
• Photograph: Banded iron formations that indicate free oxygen in oceans (2.7 bya)
Oxygen Revolution
• Oxygen Evolution of aerobic respiration
• Increased ATP production More energy
• Photo Credit of Bacillus cereus on blood agar: CDC, 2006, Wikimedia Commons
Prokaryotic Cells
• Review – Reproduction
(binary fission)
– Membrane transport
• Gases• Water• Wastes• Ions
• Photo: Dr. Vincent A. Fischetti, Laboratory of Bacterial Pathogenesis and Immunology, Rockefeller University, Courtesy of NOAA
Photoautotrophs
• Photoautotrophs can be:– Non-oxygenic– OxygenicPhoto: Cyanobacteria that uses oxygenic photosynthesis
Domain Bacteria
• Prokaryote• Cell wall contains
peptidoglycan• Circular
chromosome– No histones
• Photo: Beggiatoa, a sulfur bacterium. Granules contain elemental sulfur produced by the cell’s metabolism.
Domain Archaea
• Prokaryote• No peptidoglycan
in cell wall• Circular
chromosome– Histones
• Photo: Halobacterium, a salt-loving (halophile) archaean. Courtesy of NASA.
Archaeans
• Most known archaeans are extremophiles
• Picture Credit of Hydrothermal Vent Archeans, Extreme Thermophiles: Courtesy of NOAA
Methanogens
Left: Methanopyrus kandleri, 2006, PMPoon, Wikimedia Commons
Right: Methanothermobacter, Tashiror, 2006, Wikimedia Commons
Acidophiles
Left: Sulfolobus, Xiaoya Xiang,2007, Wikimedia Commons
Right: Acid mine drainage, Carol Stroker, 2005, NASA Wikimedia Commons
Archaeans in “Normal Environments”
• Oceans, soils,freshwater
Photo Credit of Worldwide View of Plankton, 1998-2004: NASA, Wikimedia Commons
Note: Archaeans are an important part of plankton. Up to 20% of world’s biomass may be archaeans.