Early Earth and the Origin of Life

Phylogeny Traces life backward to common ancestors. How did life get started?

Fossil Record Earliest - 3.5 billion years old. Earth - 4.5 billion years old.

Prokaryotes Fossil Modern

Bacterial Mats

Point Life on earth started relatively soon after the earth was formed.

Chemical Evolution The evolution of life by abiogenesis.

Steps 1. Monomer Formation 2. Polymer Formation 3. Protobiont Formation 4. Origin of Heredity

Primitive Earth Conditions Reducing atmosphere present. Simple molecules Ex: H2O vapor CH4 methane Hydrogen H2, Ammonia NH3

Complex Molecule Formation Requires energy sources: UV radiation Radioactivity Heat Lightning

Oparin and Haldane 1920s Hypothesized steps of chemical evolution from primitive earth conditions.

Miller and Urey, 1953 Tested Oparin and Haldane’s hypothesis. Experiment - to duplicate primitive earth conditions in the lab.

Results Organic monomers formed including Amino Acids.

Other Investigator's Results All 20 Amino Acids Sugars Lipids Nucleotides ATP

Hypothesis Early earth conditions could have formed monomers for life's origins.

Polymer Synthesis Problem: Monomers dilute in concentration. No enzymes for bond formation.

Possible Answer 1. Clay 2. Iron Pyrite

Explanation Lattice to hold molecules, increasing concentrations. Metal ions present which can act as catalysts.

Protobionts Aggregates of abiotically produced molecules. Exhibit some properties of life. Ex: Osmosis Electrical Charge Fission

Protobionts

Protobiont Formation Proteinoids + H2O  microspheres Liposomes + H2O  lipid membranes

Coacervates Colloidal droplets of proteins, nucleic acids and sugars surround by a water shell. Will form spontaneously from abiotically produced organic compounds.

Summary Protobionts have membrane-like properties and are very similar to primitive cells. Start for selection process that lead to cells?

Question ? Where did the energy come from to run these early cells?

Answer ATP. Reduction of sulfur compounds. Fermentation.

Genetic Information DNA  RNA  Protein Too complex for early life. Other forms of genetic information?

RNA Hypothesis RNA as early genetic information.

Rationale RNA polymerizes easily. RNA can replicate itself. RNA can catalyze reactions including protein synthesis. Ribozymes

Ribozymes RNA catalysts found in modern cells. e.g. ribosomes Possible relic from early evolution?

Molecular Cooperation Interaction between RNA and the proteins it made. Proteins formed may serve as RNA replication enzymes.

Molecular Cooperation Works best inside a membrane. RNA benefits from the proteins it made.

Selection favored: RNA/protein complexes inside membranes as they were the most likely to survive and reproduce.

DNA Developed later as the genetic information Why? More stable than RNA

Alternate View Life developed in Volcanic Vents.

Volcanic Vents Could easily supply the energy and chemical precursors for chemical evolution. Most primitive life forms are the prokaryotes found in or near these vents.

New Idea Life started in cold environments. Interface between liquid and solid allows concentration of materials and formation of polyomeres. Molecules last longer too.

Modern Earth Oxidizing atmosphere. Life present. Prevents new abiotic formation of life.

Hypothesis Life as a natural outcome of chemical evolution. Life possible on many planets in the universe.

Kingdom Highest Taxonomic category Old system - 2 Kingdoms 1. Plant 2. Animal

5 Kingdom System R.H. Whittaker - 1969 System most widely used today.

Main Characteristics Cell Type Structure Nutrition Mode

Monera Ex: Bacteria, Cyanobacteria Prokaryotic

Protista Ex: Amoeba, Paramecium Eukaryotic Unicellular or Colonial Heterotrophic

Fungi Ex: Mushrooms, Molds Eukaryotic Unicellular or Multicellular Heterotrophic - external digestion Cell wall of chitin

Plantae Ex: Flowers, Trees Eukaryotic Multicellular Autotrophic Cell wall of Cellulose/Silicon

Animalia Ex: Animals, Humans Eukaryotic Multicellular Hetrotrophic - internal digestion No cell wall Motile

Other Systems Multiple Kingdoms – split life into as many as 8 kingdoms. Domains – a system of classification that is higher than kingdom.

3 Domain System Based on molecular structure for evolutionary relationships. Prokaryotes are not all alike and should be recognized as two groups. Gaining wider acceptance.

3 Domains 1. Bacteria – prokaryotic. 2. Archaea – prokaryotic, but biochemically similar to eukaryotic cells. 3. Eucarya – the traditional eukaryotic cells.

Summary Systematics is still evaluating the evolutionary relationships of life on earth. Be familiar with the conditions of primitive earth. Know the steps of chemical evolution.

Summary Recognize the 5 Kingdoms. Know about Domains.