Transcript Origin of Life on Earth

Origin of Life on Earth
What do we know about early
life on Earth?
• Evidence from rocks called stromatolites
• Consist of banded domes of rock
• Similar to layered mats found in salt
marshes today
Stromatolites
• Large mats found at
Shark Bay, Western
Australia are
considered “living
stromatolites”
Cross section of a stromatolite
• Notice the layers of
microbes known as
fossilized “mats” of
bacteria
What do we know about early
life on Earth?
• Evidence in individual fossilized cells
suggest life as early as 3.2-3.5 billion years
ago
• See Fig. 5.2 (text)
What do we know about early
life on Earth?
• Evidence from analysis of ratios of carbon
isotopes in ancient rocks (C13, C 12)
• Rocks older than 3.85 billion years may had
organic life
If life existed 3.85 billion years
ago…
• Would we find traces of it?
• No! Why?
Tree of life as evidence?
Evidence of early life on Earth
• Stromatolites
• Fossilized cells
• Use the tree of life to determine
relationships
What was the early Earth like?
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Water, no land
No oxygen present
No protection from UV radiation
Shallow ponds the home of first life
Early life needs better energy
source
• deep sea vents
•
http://www.ocean.udel.edu/deepsea
/level-1/geology/smoker.mov
• Surface hot springs
Miller-Urey Experiment
• Used flasks to
simulate chemical
conditions present on
Earth
• Generated organic
molecules…but not
enough for life
Where could organic compounds
come from?
• Impacts (asteroids, comets, meteors)
• Chemical reactions near deep sea vents
What do we have so far?
• Organic compounds
• Environment that can produce these
compounds
• What else do we need??
What type of molecule would be
best at replication?
• DNA?
• RNA?
1980’s discover replicating RNA
• Cech and colleagues identify that RNA can
self-replicate….acts as enzymes
• Called ribozymes
If it was an “RNA World”
If not “RNA World” then what?
• DNA…still have the “chicken and egg
problem”
• Proteins were first
• Double origin, proteins and replication of
nucleic acids
• Clay crystals serve as scaffolding
How can we get to a more “celllike” model?
• Need to confine the organic compounds in
membranes
• “pre-cells” formed from
– Amino acids
– Lipids mixed with water
Summary of early life…takes
many steps
• Need materials to form “organic soup”
• Generate more complex molecules
(polymers)
• Membranes formed
• Natural selection of RNA leads to DNA
model
Is this the only idea behind early
life on Earth?
• No
• What is panspermia?
Evidence to support Panspermia
• Organic molecules in meteorites
• Microbes can survive moderate time in
space
When did bacteria evolve
compared to other cells?
A look at early microbes
• General characterisitics
Deep Sea vents model early life
for microbes
Photosynthesis changed the Earth
• Organisms could obtain energy from the
sunlight
• Evolved slowly…first just pigments trap uv
light
• Purple and green sulfur bacteria are much
like early photosynthetic microbes
Photosynthesis using water
• Evolved 3.5 billion
years ago
• Earliest fossils
resemble modern
cyanobacteria (bluegreen algae)
Cyanobacteria in Lake
Sammamish
• Sept 1997
• Algal bloom of
Microcystis aeruginosa