The prokaryotes The first cells Bacillus anthracis Thermophilic archaebacteria © 2016 Paul Billiet ODWS

Origins Evidence for prokaryotic cells is found as early as 3.9 billion years ago The prokaryotes had the Earth to themselves for another 2.4 billion years Prokaryotes show an extraordinary diversity of biochemistry Structurally prokaryotes are quite small and simple (1-10µm in diameter). © 2016 Paul Billiet ODWS

Where? “(a) warm little pond, with all sorts of ammonia and phosphoric salts, lights, heat, electricity, etc. present, so that a protein compound was chemically formed ready to undergo still more complex changes” Charles Darwin (1871) Organic compounds would accumulate in the Earth's oceans until they "reached the consistency of hot, dilute soup." JBS Haldane (1929) Deep sea hydrothermal vents? Volcanoes? Outer space? © 2016 Paul Billiet ODWS

Panspermia (aka cosmozoan theory) Life came from somewhere else and seeded Earth The support for this depends up on evidence that life exists elsewhere than on Earth and the evidence that it may travel through open space. © 2016 Paul Billiet ODWS

Exobiology Mars Viking Probe (1976) revealed conflicting evidence of life Mariner Probe (1997) did not reveal any more evidence Evidence of water and methane on Mars Venus has inhospitable conditions (surface temperatures of over +400°C). Viking © 2016 Paul Billiet ODWS

Water and geothermal energy is the key The moons of Jupiter and Saturn? Europa covered in ice? Io has volcanic activity Titan has organic molecules present. Europa © 2016 Paul Billiet ODWS

Life can survive in outer space Bacteria, inadvertently left on a lunar probe Collected and cultured successfully after nearly 2 years in space Meteorites of Martian origin show early Martian atmosphere similar to Earth’s early atmosphere Also showed (debatable) evidence of bacteria transported by meteorites. Surveyor 3 © 2016 Paul Billiet ODWS

Alien Earth Antarctica Life has been shown to exist on Earth in very inhospitable conditions that could exist on other planets Antarctic dry valleys Mid-ocean ridges. earth science australia © 2016 Paul Billiet ODWS

Earliest evidence of life The origin of the Earth itself is estimated as 4.5 billion years Earliest evidence of life processes 3.9 billion years ago This leaves little time for biochemical evolution. © 2016 Paul Billiet ODWS

How did life evolve in the first place? The eternal question If it can be shown that life came from an extraterrestrial source the question still remains… How did life evolve in the first place? © 2016 Paul Billiet ODWS

Oxygen… the toxic gas The amount of free oxygen in the atmosphere increased after the evolution of photosynthesis O2 appeared from about 2.4 billion years ago and reached about 21% 1 billion years ago Obligate anaerobes either became extinct or found niches where oxygen is absent. Stromatolites, Shark Bay Australia © 2016 Paul Billiet ODWS

The Great Oxidation Event © 2016 Paul Billiet ODWS

The autotrophs began to drool Iron is soluble in water where there is no oxygen Iron rich water is produced by volcanic activity Sunlight permitted cyanobacteria to photosynthesize and produce O2 O2 combined with the iron and formed rust (iron III oxide) Rust removes the O2 from the water This carried on until the rate of photosynthesis was so great, free O2 appeared in the atmosphere (about 2.4 bn years ago) This may have been precipitated by a shortage of nickel (Ni) used in the enzymes of methanogens Methane produced by methanogen bacteria also reduced the oxygen levels. Ironband formations © 2016 Paul Billiet ODWS

The evolution of the eukaryotes Teaming up of microbes = Endosymbiosis – a large anaerobic cell teams up with an aerobic cell The aerobic prokaryote became a mitochondrion Eukaryotic cells were formed, bigger and more complex, eventually forming multicellular organisms. © 2016 Paul Billiet ODWS

The evidence for endosymbiosis Certain eukaryotic organelles have their own DNA Single naked loop of DNA, like the prokaryotes The amount of hereditary information is a lot less than free-living prokaryotes These organelles have their own ribosomes smaller (70S) than those in the cytoplasm (80S) the same size as those in prokaryotes The protein synthesis of these organelles is semi-independent of that taking place in the cytoplasm It is inhibited by the same antibiotic that affects prokaryotes (chloramphenicol). © 2016 Paul Billiet ODWS

The structural evidence Organelles are found in membrane envelopes Captured in a vacuole or vesicle by a larger cell? Organelles about the same size as a prokaryotic cell. Mitochondrion © 2016 Paul Billiet ODWS

Mitochondria Represent an aerobic prokaryote that took up residence in a larger cell Found in all the eukaryotic kingdoms (plants, animals, fungi and protoctista). Mitochondrion © 2016 Paul Billiet ODWS

Chloroplasts Cyanobacterium heterocyst Represent a cyanobacterium type of prokaryote that was trapped in ancestral plants and some protoctista. © 2016 Paul Billiet ODWS