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

2. 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

3. 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

4. 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

5. 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

6. 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
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7. 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

8. 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

9. 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

10. 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

11. 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

12. The Great Oxidation Event
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13. 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

14. 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

15. 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

16. 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

17. 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

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