Transcript CH 26: Early Earth and the Origin of Life

CH 26: Early Earth and the
Origin of Life
Presentation by Alisa Gordon,
Erica Guo, and Victoria Chen
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
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
Stromatolite
The History of life
1.
2.
3.
After the Earth’s 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
History of Life (continued)
4.
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
5.
Protists: large group of unicellular
organisms
- Plants, animals, and fungi arose from
distinct protists
Where they came from
History of Life( continued)
6.
7.
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)
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
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
Abiotic synthesis of organic
monomers
1920 – A. I. Oparin and J. B. S. Haldane
Conditions on primitive Earth favored creation
of organic compounds
Primitive Earth’s atmosphere had less
oxidizing atmosphere
Making organic molecules was facilitated by
intense UV radiation – the earth had a primitive
atmosphere
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
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 cell’s reaction, and water
dissolves polymers…So 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.
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
Examples
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
Coacervates
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