Early Earth and Origin of Life Chapter 26
Earth’s original organisms are microscopic and unicellular. • Life on Earth originated b/w 3.5- 4 billion years ago. • Earth formed 4.5 billion years ago. • Evidence of ancient prokaryotes found in rocks called stromatolites- banded domes of sedimentary rock similar to layered mats formed today in salt marshes and some warn ocean lagoons by colonies of bacteria and cyanobacteria. The layers are sediments that stick to jelly-like coats of motile microbes, which continually migrate out of one layer of sedimentand form a new one above, producing the banded pattern
Major episodes in the history of life • 1. Origin of Earth • 2. Earth cool enough for crust to solidify • 3. Origin of life (prokaryotes) • 4. RNA sequence data shows prokaryotes split into 2 groups: bacteria and archae • 5. Production of oxygen by early photosynthetic prokaryotes create aerobic atmosphere, and organisms must adapt to being aerobic, and species set to evolve • 6. Origin of eukaryotes: protists- large, disparate group of unicellular eukaryotes and some closely related multicellular organisms • 7. Origin of multicellular organisms: Plant, fungi, and animals. (fungi more related to animals than plants) in PreCambrian • 8. Late PreCambrian: oldest animal fossils • 9. Plants and symbiotic fungi colonize land: Paleozoic • 10. Extinction of Dinosaurd at end of Mesozoic • 11. First humans at end of Cenozoic
First organisms were products of chemical evolution in 4 stages: • 1. The abiotic (nonliving) synthesis and accumulation of small organic molecules (monomers) such as amino acids and nucleotides • 2. Joining of these monomers into polymers (proteins and nucleic acids) • 3. Aggregation of abiotically produced molecules into droplets (protobionts) that had chemical characteristics different from surroundings. • 4. Origin of heredity (before droplet stage)
Oparin-Haldane Hypothesis • In the present atmosphere, oxygen is rich and attach chemical bonds, extracting electrons. Before oxygen producing photosynthesis, Earth had a much less oxidizing atmosphere. Such a reducing (electron adding) atmosphere would have joined simple molecules to form complex ones. This requires a lot of energy, possible provided from lightning, intense UV radiation, and volcanic vapors from the atmosphere back then. Today, the oxygen has produced an ozone layer that prevents UV radiation.
Stanley Miller and Harold Urey • They tested Oparin-Haldane hypothesis by creating experiment similar to Earth’s early atmosphere: used an apparatus where a warm flask of water represented the sea. The atmosphere had (H20-water, H2-hydrogen, CH4-methane, and NH3-ammonia). Sparks were discharged in the fake atmosphere to mimic lightning. A condenser cooled the atmosphere, raining water and other dissolved compunds back to the sea. As material circulated through the apparatus, the solution in flask turns clear murky brown. After one week, variety of organic compounds including amino acids that make up proteins of organisms, were found.
Protobionts • Living cells may have been preceded by protobionts (abiotically produced molecules)- cannot reproduce, but maintain internal environment diff. from surroundings and exhibit some properties similar to life such as metabolism and excitability. • Coacervate (a protobiont) is a stable droplet that tends to self-assemble when a suspension of macromolecules is shaken. Hydrophobic macromolecules surround coacervate, which absorb substrates from enzymes and release products of reactions catalyzed by the enzymes.
Protobionts could have formed spontaneously from abiotically produced organic compounds: • Microspheres made by cooling solutions of proteinoids (polypeptides created abiotically from amino acids polymerized on hot surfaces). Microspheres grow by absorbing free proteinoids until they reach unstable size, and split to form daughter microspheres. • In aqueous environ., certain lipids self-assemble to form liposomes, which some grow by engulfing smaller liposomes and then splitting, other times giving birth” to smaller liposomes.
RNA is first genetic material • RNA is autocatalytic, and in prebiotic world, RNA molecules capable of self-replication: • RNA acts as template for making polypeptides; and in turn the polypeptides act as enzymes that aid in the replication of RNA molecules. • Within a membrane, polypeptides aid the replication of only the template RNA genes.
Were RNA or DNA genes preceded by simpler hereditary systems? • Amino-adenosine triacid ester (AATE) , consists of amino adenosine and an ester. • AATE can catalyze synthesis of another AATE by acting as a template.
THE END • This has been a slideshow by SUPER-LAUREN! She rox sox!