The Origin and Early History of Life

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The Origin and Early History of Life

• Chapter 4

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Outline

• Origin of Life Hypotheses
• Chemical Evolution
• Cell Origin Theories
• Bubble Theories
• Prokaryotic Cells
• Archaebacteria
• Bacteria
• Eukaryotic Cells
• Extraterrestrial Life

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What do we know?

• 1.5 Million species identified so far
• Many more remain unidentified

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Are we alone?

1. Yes
2. No

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Which one represents possible origin of life on
earth?

1. Extraterrestrial aliens brought it
2. Came with meteors from other planets
3. Some superhuman powers created it
4. Chemicals from primordial soup combined to make
   life
5. None of the above

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What have we learned so far?

• Cell theory
• All living organisms are made of cells, and all
  living cells come from other living cells.
• Molecular basis of inheritance
• DNA encodes genes which make-up and control
  living organisms.
• Evolutionary change
• Life-forms have evolved varying characteristics
  to adapt to varied environments.
• Evolutionary conservation
• Some characteristics of earlier organisms are
  preserved and passed on to future generations.

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Where the first cell came from?

• Or.Can life arise from non-life?
• Can we test this scientifically?
• Conditions on early earth
• Formation of organic molecules
• Chemical evolution
• Primitive cell
• Prokaryotes
• Eukaryotes
• Multicellular organisms

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Conditions on Early Earth-Reducing Atmosphere

• Life most likely emerged under high-temperature
  conditions.
• Early atmosphere is often referred to as a
  reducing atmosphere.
• exact conditions unknown
• ample availability of hydrogen atoms
• very little oxygen

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Origin of Life - Location

• Oceans edge
• bubble hypotheses
• Under frozen seas
• problematic due to necessary conditions
• Deep in Earths crust
• byproduct of volcanic activity
• Within clay
• positively-charged clay
• Deep-sea vents
• conditions suitable for Archaea

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Miller-Urey Experiment

• Attempted to reproduce early reducing atmosphere
  and produce organic compounds from inorganic
  materials
• hydrogen-rich
• electrical discharges
• Produced
• amino acids
• carbohydrates
• lipids
• nucleotides

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Chemical Evolution

• If life originally arose from non-life, how might
  this have happened?
• Consider the following scenario
• Synthesis and accumulation of small organic
  molecules
• Joining of these monomers into polymers
• Aggregation of these molecules into droplets to
  form localized microenvironments
• Origin of heredity

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Polymer Formation

• Sidney Fox (University of Miami) demonstrated the
  abiotic polymerization of organic monomers
• Polymers were formed when dilute solutions of
  organic molecules were dripped onto hot sand,
  clay, or rock
• Proteinoids
• Clay can serve to concentrate these molecules
• Monomers bind to charged sites on clay particles
• Metal ions in clay have catalytic function

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Which came first?

• DNA
• RNA
• Protein

Most Likely
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Abiotic RNA Replication
Remember RNA enzymes?
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Lets make something with those molecules

• Aggregations of abiotically produced molecules
• Preceded living cells
• Laboratory experiments have demonstrated their
  formation from organic compounds
• Protobionts and liposomes

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Origin of protobiots

• Bubble theories (Oparin)

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PROTO-CELLS

• Chemical evolution ultimately led to the
  formation of proto-cells
• Membrane-surrounded sacs containing genetic
  material and metabolically-active molecules
• Such structures have been experimentally produced
• From these proto-cells, cells ultimately arose

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Earliest Cells

• Microfossils have been found in rocks as old as
  3.5 billion years old.
• resemble prokaryotes

Stromatolites
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EARLIEST LIFE

• The earliest cells were prokaryotic
• Lack a membrane-bound nucleus
• Early in the history of life, populations
  diverged into two major lineages
• ? bacteria
• ? archaea eukaryotes

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Archaebacteria

• Extreme-condition prokaryotes
• lack peptidoglycan in cell walls
• methanogens
• extreme halophiles
• extreme thermophiles
• thought to have split from Bacteria 2 bya.

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Bacteria

• Second major group of prokaryotes
• strong cell walls
• simpler gene structure
• contains most modern prokaryotes
• includes photosynthetic bacteria
• cyanobacteria

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EARLIEST LIFE

• How do we know that domain Eukarya is more
  closely related to domain Archaea than to domain
  Bacteria?
• Analysis of rRNAs and other highly conserved
  genes and proteins provide the strongest
  evidence

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First Eukaryotic Cells

• Eukaryotes probably arose about 1.5 bya.
• Internal membrane-bound structures such as
  mitochondria and chloroplasts are thought to have
  evolved via endosymbiosis.
• Energy-producing bacteria were engulfed by larger
  bacteria.
• beneficial symbiotic relationship

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First Eukaryotic Cells

• Sexual reproduction
• Eukaryotic cells can reproduce sexually, thus
  allowing for genetic recombination.
• Genetic variation is the raw material necessary
  for evolution.
• Multicellularity
• arisen many times among eukaryotes
• fosters specialization

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Development of new branches on the TREE
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TAXONOMY
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Extraterrestrial Life

• Universe has 1020 stars similar to our sun.
• Conditions may be such that life has evolved on
  other worlds in addition to our own.
• ancient bacteria on Mars.
• largest moon of Jupiter, Europa, covered with
  ice.
• liquid water may be underneath

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The Domains and Kingdoms
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What they have and what they dont
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What about this group?
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Summary

• Fundamental Properties of Life
• Origin of Life Hypotheses
• Chemical Evolution
• Cell Origin Theories
• Bubble Theories
• Prokaryotic Cells
• Archaebacteria
• Bacteria
• Eukaryotic Cells
• Extraterrestrial Life

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