The Origin and Evolution of Life

1
The Origin and Evolution of Life

• Chapter 20

2
20.1 The Big Bang

• 12-15 billion years ago all matter was compressed
  into a space the size of our sun
• Sudden instantaneous distribution of matter and
  energy throughout the known universe

3
Archeon Eon and Earlier

• 4,600 mya Origin of Earth
• 4,600 - 3,800 mya
• Formation of Earths crust, atmosphere
• Chemical and molecular evolution
• First cells (anaerobic bacteria)

4
Earth Forms

• About 4.6 and 4.5 billion years ago
• Minerals and ice orbiting the sun started
  clumping together
• Heavy metals moved to Earths interior, lighter
  ones floated to surface
• Produced outer crust and inner mantle

5
Earth Is Just Right for Life

• 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

6
First Atmosphere

• Hydrogen gas
• Nitrogen
• Carbon monoxide
• Carbon dioxide
• No gaseous oxygen

7
Origin of Organic Compounds

• Amino acids, other organic compounds can form
  spontaneously under conditions like those on
  early Earth
• Clay may have served as template for complex
  compounds
• Compounds may have formed near hydrothermal vents

8
Stanley Millers Experiment
electrodes
to vacuum pump
spark discharge
CH4 NH3 H2O H2
gases
water out
condenser
water in
water droplets
water containing organic compounds
boiling water
Figure 20.3 b Page 326
liquid water in trap
9
20.2 Chemical Evolution
chlorophyll a

• Spontaneous formation of porphyrin rings from
  formaldehyde
• Components of chlorophylls and cytochromes

formaldehyde
porphyrin ring system
Figure 20.4  Page 720
10
RNA World

• DNA is genetic material now
• DNA-to-RNA-to-protein system is complicated
• RNA may have been first genetic material
• RNA can assemble spontaneously
• How switch from RNA to DNA might have occurred is
  not known

11
Proto-Cells

• Microscopic spheres of proteins or lipids can
  self assemble
• Tiny sacs like cell membranes can form under
  laboratory conditions that simulate conditions in
  evaporating tidepools
• Nanobes may resemble proto-cells

12
Possible Sequence
membrane-bound proto-cells
self-replicating system enclosed in a selectively
permeable, protective lipid sphere
Figure 20.5  Page 331
13
20.3 Proterozoic Eon

• Origin of photosynthetic Eubacteria
• Noncyclic pathway first
• Cyclic pathway next
• Oxygen accumulates in atmosphere
• Origin of aerobic respiration

14
The First Cells

• Originated in Archeon Eon
• Were prokaryotic heterotrophs
• Secured energy through anaerobic pathways
• No oxygen present
• Relied on glycolysis and fermentation

15
History of Life
ARCHAEBACTERIAL LINEAGE
ANCESTORS OF EUKARYOTES
Noncyclic pathway of photosynthesis
Cyclic pathway of photosynthesis
ORIGIN OF PROKARYOTES
Aerobic respiration
Figure 20.6  Page 332
3.8 bya
3.2 bya
2.5 bya
16
History of Life
ARCHAEBACTERIA
Extreme halophiles
Methanogens
Extreme thermophiles
ORIGINS OF ANIMALS
EUKARYOTES
ORIGINS OF EUKARYOTES
Animals
Heterotrophic protistans
ORIGINS OF FUNGI
Fungi
Photosynthetic protistans
ORIGINS OF MITOCHONDRIA
Plants
ORIGINS OF PLANTS
ORIGINS OF CHLOROPLASTS
EUBACTERIA

Photosynthetic oxygen producers
Other photosynthetic bacteria

Chemotrophs, heterotrophs
Figure 20.6  Page 332
1.2 bya
900 mya
435 mya
present
17
Advantages of Organelles

• Nuclear envelope may have helped to protect genes
  from competition with foreign DNA
• ER channels may have protected vital proteins

DNA
infolding of plasma membrane
Figure 20.10  Page 335
18
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