CH 26: Early Earth and the Origin of Life

1
CH 26 Early Earth and the Origin of Life

• Presentation by Alisa Gordon, Erica Guo, and
  Victoria Chen

2
The History of Life An Introduction

• Earth was formed about 4.5 billion years ago
• Life is thought to have formed between 3.5 and 4
  billion years ago
• Evidence? Isotopes in carbon found in 3.8 billion
  year old rocks in Greenland

3
What was the first life?

• Prokaryotes were probably the first organisms
• Evidence through Stromatolites, banded domes of
  sedimentary rock
• Stromatolites are similar layered mats in salt
  marshes formed today by colonies of bacteria.
• Oldest known fossils of Living organisms are
  found in 3.5 billion year old Stromatolites in
  Western Australia

4
Stromatolite
5
The History of life

• After the Earths crust cooled and solidified, we
  believe that prokaryotes were the first to
  originate
• Bacteria and Archaea became the two best thriving
  prokaryotes (their split happened 3 billion years
  ago)
• Evolution of aerobic life began 2.5 billion years
  ago, thanks to the presence of O2 from early
  photosynthetic prokaryotes

6
History of Life (continued)

• Oldest Eukaryotic fossils 1.7 billion years
  ago, but evolved hundreds of millions of years
  before hand
• -evidence that they evolved from symbiotic
  communities of prokaryotes
• Protists large group of unicellular organisms
• - Plants, animals, and fungi arose from distinct
  protists

7
Where they came from
8
History of Life( continued)

• Oldest animal fossils 700 million years ago
  from (specifically, the Precambrian Era)
• - Fauna not too diverse
• For 3.5 billion years, life was confined to
  aquatic environment (90 of its existence)

9
The Origin of Life

• The first cells may have originated by chemical
  evolution on a young Earth
• Life on Earth developed from nonliving materials
• Lightning, volcanic activity, meteorite
  bombardment, ultraviolet radiation
• Created environment in which early stages of
  biological inception was inevitable

10
How did they evolve?

• One Hypothesis
• Abiotic synthesis and accumulation of small
  organic molecules
• Joining of molecules to polymers proteins,
  nucleic acids
• Aggregation of molecules into droplets
  Protobionts
• Origin of heredity

11
Abiotic synthesis of organic monomers

• 1920 A. I. Oparin and J. B. S. Haldane
• Conditions on primitive Earth favored creation of
  organic compounds
• Primitive Earths atmosphere had less oxidizing
  atmosphere
• Making organic molecules was facilitated by
  intense UV radiation the earth had a primitive
  atmosphere

12
Abiotic synthesis of organic monomers

• 1953 Stanley Miller and Harold Urey
• Tested Oparin-Haldane hypothesis
• Included variety of amino acids and other organic
  compounds in living organisms
• Apparatus used to simulate chemical dynamics on
  primitive Earth
• Laboratory analogs have produced 20 amino acids
  found in organisms
• Many doubt atmosphere was reason for development,
  believe that submerged volcanoes and deep-sea
  vents provided the resources needed

13
(No Transcript)
14
Laboratory Stimulations

• Abiotic synthesis of complex organic molecules
  was bound to happen
• Smaller organic polymers (like proteins) had to
  join
• No enzymes to catalyze a cells reaction, and
  water dissolves polymersSo how did they?
• Answer- Polymerization occurs when dilute
  solutions of organic monomers dripped onto hot
  sand, clay or rock
• Using this polymerization method, we can make
  proteinoids, polypeptides produced by abiotic
  synthesis.

15
Substrates

• Clay is important substrate for the
  polymerization reactions steps to life
• Concentrates amino acids and other organic
  molecules and binds them with the clay particles
• Iron and zinc function like catalysts
• Alternative to clay Iron pyrite (Fools gold)
• Hypothesized to be a substrate by Gunter
  Wachterhauser

16
Examples
17
Protobionts

• Protobionts aggregates of abiotically produced
  molecules
• Not capable of reproduction, but have metabolism
  and excitability
• Have different internal chemical balance then its
  environment
• Coacervates are droplets that reassemble
  themselves when macromolecules shaken

18
Coacervates
19
More on Protobionts

• Form spontaneously from abiotically produced
  organic compounds
• Have protein membrane that swell or shrink in
  different salt concentrations
• Discharge voltage like nerve cells
• Protobionts that formed long ago though would not
  have had refined enzymes, which meant they had no
  inherited instruction