Transcript Lecture Powerpoint Here

The Origin and Early
Evolution of Life
Lecture 19
The Big Bang
 12-15 (13.8) billion years ago all matter was
compressed into a space the size of?
 Our Galaxy
 Our Solar System
 Our Plant
 Our Atom
 Sudden instantaneous distribution of matter and
energy throughout the known universe
Timeline
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4.6 to 3.8 billion years ago - Leads to solid crust
3.8 Water forms
2.8 to 3.2 - Life starts as prokaryotic cells
1.5 Eukaryotic cells develop
545 Cambrian explosion
500 Fish
350 Amphibians
300 Reptiles
1.6 humans
Timeline: Archaean Eon and
Earlier
 4,600 mya: Origin of Earth
 4,600 - 3,800 mya (about 800 million years)
 Formation of Earth’s crust, atmosphere…
 Formation of the Moon
 Chemical and molecular evolution only
 Then came the First cells (anaerobic bacteria)
Earth Forms
 About 4.6 billion years ago
 Gas, Minerals and ice orbiting the sun
started clumping together
 Heavy metals moved to Earth’s interior,
lighter ones floated to surface
 Iron core
 Produced outer crust and inner
mantle
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First Atmosphere
 Hydrogen gas
 Nitrogen
 Carbon monoxide
 Carbon dioxide
 No gaseous oxygen
Earth Is “Just Right” for Life
 IF…Earth was;
 Smaller in diameter, gravity would not be
great enough to hold onto atmosphere
 Closer to sun, water would have evaporated
 Farther from sun, water would have been
locked up as ice
Stanley Miller’s Experiment
 Mixed methane,
hydrogen,
ammonia, and
water
 Simulated lightning
 Amino acids and
other small
molecules formed
Animation
electrodes
to
vacuum
pump
CH4
NH3
H 2O
H2
spark
discharge
gases
water out
condenser
water in
water droplets
boiling water
water containing
organic compounds
liquid water in trap
How Did Cells Originate?
 In the first 600 million years or so of Earth
history, enzymes, ATP, and other crucial
organic compounds probably assembled
spontaneously - nothing came of it!
 Then, by a still disputed mechanism, the
concoction came together randomly to make
some primitive organic molecule…
Possible Sequence
membrane-bound proto-cells
living cells
self-replicating system enclosed in a
selectively permeable, protective lipid sphere
DNA
RNA
formation of
protein-RNA systems,
evolution of DNA
enzymes and
other proteins
formation of
lipid spheres
spontaneous formation of lipids,
carbohydrates, amino acids, proteins,
nucleotides under abiotic conditions
RNA World
 DNA is genetic material now
 DNA-to-RNA-to-protein system is
complex!
 RNA may have been first genetic material
 RNA can assemble spontaneously
 How switch from RNA to DNA might have
occurred is not known
The First Cells
 Originated in Archaean Eon
 There were prokaryotic cells
 These were heterotrophs
 Secured energy through anaerobic pathways
 No oxygen present, therefore they must have
 Relied on glycolysis and fermentation only!
Proterozoic Eon
 FIRST
 Origin of photosynthetic eubacteria, as a result…
 SECOND
 Then, Oxygen accumulates in atmosphere, and
 THIRD
 Origin of aerobic respiration
Advantages of Organelles
 Nuclear envelope may have
helped to protect genes from
competition with foreign DNA
 ER channels may have similarly
protected vital proteins
…
Possible Origin of ER
DNA
infolding of plasma membrane
Theory of Endosymbiosis
 Lynn Margulis
 Mitochondria and chloroplasts are the
descendents of free-living prokaryotic
organisms
 Prokaryotes were engulfed by early
eukaryotes and became permanent internal
symbionts
 http://www.sumanasinc.com/webcontent/anis
amples/nonmajorsbiology/organelles.html
Evolutionary Tree
hydrogen-rich anaerobic atmosphere
atmospheric oxygen, 10%
archaean
lineage
ancestors of
eukaryotes
endomembrane
system and nucleus
cyclic pathway
of photosynthesis
origin of
prokaryotes
3.8 billion
years ago
noncyclic pathway
of photosynthesis
aerobic respiration
3.2 billion
years ago
2.5 billion
years ago
Evolutionary Tree