Understanding points
A2.1.1 Conditions on early Earth and the pre-biotic formation of carbon compounds (HL only)
A2.1.2 Cells as the smallest units of self-sustaining life (HL only)
A2.1.3 Challenge of explaining the spontaneous origin of cells (HL only)
A2.1.4 Evidence for the origin of carbon compounds (HL only)
A2.1.5 Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers (HL only)
A2.1.6 RNA as a presumed first genetic material (HL only)
A2.1.7 Evidence for a last universal common ancestor (HL only)
A2.1.8 Approaches used to estimate dates of the first living cells and the last universal common ancestor (HL only)
A2.1.9 Evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents (HL only) |
Early Earth conditions
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High CH₄ and CO₂ concentrations due to volcanic activities and meteorite bombardment → more greenhouse gasses → higher temperatures
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UV penetration to Earth’s surface due to lack of ozone layer and frequent lightning → triggered various chemical reactions
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Miller-Urey Experiment: mimicked early Earth conditions to show the synthesis of organic carbon compounds from inorganic gasses that represent the pre-biotic atmosphere
Developments required for the origin of life
Catalyst | To control the necessary chemical reactions |
Self-assembly | Formation of polymers from smaller carbon compounds |
Compartmentalization | A membrane to enclose cell contents
Amphipathic nature of phospholipids allows spontaneous assembly of bilayer |
Self-replication | Basis of inheritance of successful variants
RNA is speculated to be the first genetic material because it can self-replicate and also function as a catalyst |
Pasteur’s experiments
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Falsified the concept of spontaneous generation (cells come from non-living things)
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Conclusion: cells are from pre-existing cells
Methodology
Broth in flask is boiled to kill pre-existing micro-organisms (create a sterile environment)
Control Results
As broth cools, condensing water collects, sealing mouth of flask (no growth will occur)
Experimental Results
If neck is broken, outside air can carry microorganisms into broth (contamination)
Conclusion
Cells can only arise from preexisting cells
Last universal common ancestor (LUCA)
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All living organisms today share the same genetic code
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This suggests the presence of a LUCA that gave rise to all modern organisms
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Common genes shared by bacteria and archaea suggest that LUCA lived near hydrothermal vents
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Hydrothermal fluids of 60-90℃
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High hydrogen, methane, ammonia, and sulfides as energy supply
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CO₂ to synthesize organic compounds
Techniques to date the origin of life
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Study of geological layers and rocks
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Carbon dating using the proportion of ¹³C and ¹²C
