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The Archean Eon. 3800 m.y. Subdivisions of the Archean - ERAS. 2.5 Ga. 2.8 Ga. 3.2 Ga. 3.6 Ga. 3.8 Ga. Origins of Life Basic minimum requirements for life: Membrane-enclosed capsule to contain bioactive chemicals Energy-capturing chemical reactions (to promote other reactions)
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The Archean Eon 3800 m.y
Subdivisions of the Archean - ERAS 2.5 Ga 2.8 Ga 3.2 Ga 3.6 Ga 3.8 Ga
Origins of Life • Basic minimum requirements for life: • Membrane-enclosed capsule to contain bioactive chemicals • Energy-capturing chemical reactions (to promote other reactions) • Chemical system for replication • RNA (ribonucleic acid) thought to be a very important molecule for early life formation: • RNA itself is capable of storing genetic information • RNA can also help catalyze chemical reactions and build molecules • Once RNA-based life was established, natural selection works to quickly evolve more efficient DNA-based system of replication, and more protein-based biochemical machinery • Did inorganic substances, like clay and pyrite, help organize and polymerize organic molecules, eventually allowing them to organize to a point for independent replication?
Experiments of the 50s and 60s: • Showed that organic molecules (amino acids) could form from the reaction of atmospheric gas, electricity, and heat • Demonstrated that drying and re-wetting of organic compounds could produce cell-like membranes and simple proteins • Therefore, was believed that life • arose in shallow pools • However, these compounds would have been exposed to harsh UV light and oxygen –would have destroyed any organic compounds
Chemoautotrophs? – Archaebacteria • Biologists have discovered simple bacteria in super-heated waters in hot springs and in deep-ocean volcanic vents (hyperthermophiles) • Water is close to boiling point and rich in sulfur and sulfur compounds • These bacteria feed directly on the sulfur for their metabolic energy needs
These bacteria appear to be most primitive life form on Earth, and their mode of life argues for life arising in the deep ocean at hydrothermal/volcanic vents dotting sea floors (near rifting zones) Vents would have provided the chemical and heat energy, chemical an mineral compounds, and protection from O and UV
Fossil life Earliest indirect evidence - BIF of the Isua Supergroup (3.8+ Ga – latest Hadean or Eoarchean) contains graphite (C) This graphite has a C12-C13 ratio identical to living organisms Earliest fossil evidence – Warrawoona Group rocks in Australia (~3.5 Ga – Paleoarchean) and slightly younger Onverwacht Group of South Africa… …sedimentary structures that may be stromatolites
Stromatolites Finely layered, mound-shaped accumulations of mud trapped by mats of blue-green algae (cyanobacteria). Primitive photosynthetic procaryotes (bacteria) that grow in marine environments. Rare in early Archean but become increasingly common in mid- to later Archean
Ultra fine-grained Archean cherts in Australia (3.5 Ga – Paleoarchean) preserve filimentous structures resembling modern cyanobacteria Also, cells in apparently different stages of division occur in rocks of the 3.0 Ga (Meosarchean) Fig Tree Group of South Africa Life does not appear to change much for the next 1.5 Ga (Proterozoic Eon), consisting of stromatolites and cyanobacteria
