Chapter 26 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. 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, CH4, H2, 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

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. Rs and Ps developed much later.

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

RNA Hypothesis RNA as early genetic information.

Rational RNA polymerizes easily. RNA can replicate itself. RNA can catalyze reactions including

protein synthesis.

Ribozymes RNA catalysts found in modern cells. 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 For RNA/protein complexes inside

membranes.

DNA Developed later as the genetic information

Why? More stable than RNA

Alternate Views

1. Panspermia

2. Volcanic Vents

Panspermia Organic compounds for life from outer

space. Brought to earth by comets and

meteorites.

Evidence Organic molecules are found in space

and in meteorites.

Volcanic Vents Could easily supply the energy and

chemical precursors for chemical evolution.

Evidence – ecosystems that are around the sea floor volcanic vents.

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

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. Recognize alternate systems for

classification.