The Earth and The Origin of Life
(Chapter 26)
Introductory Questions #1
1.
2.
3.
4.
5.
6.
7.
What were the molecules thought to exist in the
early atmosphere?
What does it mean when we say that this early
atmosphere was a “reducing” atmosphere?
What is the significance of Miller’s experimetn in
the 1950’s?
What are protobionts and microspheres?
Where can Stomatolites be found? What are they
composed of?
What is the predominant thought of how
Polymerization might of occurred?
Was the first organisms thought to be heterotrophs
or Autotrophs? Explain.
Chemical Evolution & Formation of
Macromolecules

Solar System: formed approx. 12 billion years ago
 Earth is Approx. 4.6 Billion Years ago
 Early Atmosphere was thought to be composed of:
–
–
–
–

CO2
CO
N2
H2S
Water Vapor
H2
NH3 (ammonia)
CH3 (methane)
Reducing Atmosphere (molecule forming)
 First Life form originated approx. 3.8 billion years
ago
Early History of life
Early History of life









Solar system~ 12 billion years ago (bya)
Earth~ 4.5 bya
Life~ 3.5 to 4.0 bya
Prokaryotes~ 3.5 to 2.0 bya
stromatolites
Oxygen accumulation~ 2.7 bya
photosynthetic cyanobacteria
Eukaryotic life~ 2.1 bya
Multicelluar eukaryotes~ 1.2 bya
Animal diversity~ 543 mya
Land colonization~ 500 mya
Three Proposed Models

Pre-Biotic Soup Hypothesis (Oparin &
Haldane)
**proposed in 1920’s**

Iron-Sulfur Hypothesis (Hydrothermal vents)

Seeded Meteorite impact
The Origin of Life






Spontaneous
generation vs.
biogenesis (Pasteur)
The 4-stage Origin of
life Hypothesis:
1- Abiotic synthesis of
organic monomers
2- Polymer formation
3- Origin of Selfreplicating molecules
4- Molecule packaging
(“protobionts”)
Organic monomers/polymer synthesis


Oparin (Rus.)/Haldane (G.B.)
hypothesis (primitive earth):
volcanic vapors (reducing
atmosphere) with lightning
& UV radiation enhances
complex molecule
formation (no O2)
Miller/Urey experiment
(1950’s):
water, hydrogen, methane,
ammonia
all 20 amino acids, nitrogen
bases, & ATP, DNA, and
RNA were formed
How Polymerization could Occur?
Clay was thought to be a possible site for
polymerization
 Binds well to organic molecules
 Contains Zinc, iron, nickel, etc serving as a
catalyst
 Has been shown to occur experimentally

Formation of the first Cells






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Began as molecular aggregates
(microspheres & protobionts)
Divide often (binary fission)
Grow larger in size
Maintain a level of homeostasis internally
Produce electrical potential across surfaces
Absorbs materials from the surface (selective
permeability)
Catalytic activity
Molecular Replication
Usually involves DNA, RNA and proteins
 All can form on clay surfaces
 Self-replication common with DNA & RNA
 Which formed first?

DNA or RNA?
Molecular Replication
Most hypothesize that RNA was the first
to form. Why?
 RNA is a versatile molecule and:

– Able to function both as an enzyme &
substrate
– Single stranded and easily forms H-bonds
– Has catalytic properties
– Can direct protein synthesis
– Folds on itself and from various shapes
Abiotic Genetic Replication

First genetic material
 Abiotic production of
ribonucleotides
 Ribozymes (RNA
catalysts)
 RNA “cooperation”
 Formation of short
polypeptides
(replication enzyme?)
 RNA~ DNA template?
Molecular cooperation led to the first
cells controlled by RNA

Oldest fossilized cells widely accepted (2 bya)
 Layers of Microorganisms & sediment called:
Stromatolites
First cells thought to be anaerobic using glycolysis as
its metabolic pathway
Heterotrophs → Photoautotrophs → Aerobes—Euk’s
(O2 increases)
(endosymbiotic theory)
The Major Lineages of Life
Figure 15.1
Key Fossil finds & Extinction Points
• Ediacaran: oldest known fossils (600 mya)
Australia
• Burgess Shale: Cambrian explosion
British Columbia
• Permian Extinction: 90% of all marine life
• Cretaceous Period: end of dinosaur fossils
Are Birds Really Dinosaurs with Feathers?
• Did birds evolve from dinosaurs?
• Evolutionary biologists investigate this
question by looking at the fossil record
• The fossil of the earliest
known bird,
Archeaopteryx,
was discovered in 1861
• Fossils of
dinosaurs with
feathers may
support the birddinosaur theory
The fossil record chronicles macroevolution
• Macroevolution consists of the major
changes in the history of life
– The fossil record chronicles these changes,
which have helped to devise the geologic time
scale
Figure 15.1
15.2 The actual ages of rocks
and fossils mark geologic time
• The sequence of fossils in rock strata
indicates the relative ages of different
species
• Radiometric dating can gauge the actual
ages of fossils
15.3 Continental drift has played
a major role in macroevolution
• Continental drift is the slow, incessant
movement of Earth’s crustal plates on the
hot mantle
Eurasian
Plate
North
American
Plate
African
Plate
Pacific
Plate
Nazca
Plate
South
American
Plate
Split
developing
Indo-Australian
Plate
Antarctic Plate
Edge of one plate being pushed over edge of
neighboring plate (zones of violent geologic events)
Figure 15.3A
Eurasia
Africa
India
South
America
MESOZOIC
Antarctica
PALEOZOIC
Millions of years ago
– Continental mergers
triggered extinctions
– Separation of
continents caused the
isolation and
diversification of
organisms
CENOZOIC
• This movement has
influenced the distribution
of organisms and greatly
affected the history of life
Laurasia
Figure 15.3B
• Continental drift explains the distribution of
lungfishes
– Lungfishes evolved when Pangaea was intact
Figure 15.3C
NORTH
AMERICA
ASIA
EUROPE
AFRICA
SOUTH
AMERICA
AUSTRALIA
= Living lungfishes
= Fossilized lungfishes
Figure 15.3D
15.4 Connection: Tectonic
trauma imperils local life
• Plate tectonics, the movements of Earth’s
crustal plates, are also associated with
volcanoes and earthquakes
– California’s
San Andreas
fault is a
boundary
between two
crustal plates
San Andreas fault
San Francisco
Santa Cruz
Los Angeles
Figure 15.4A
• By forming new islands, volcanoes can
create opportunities for organisms
– Example: Galápagos
• But volcanic activity can also destroy life
– Example: Krakatau
Figure 15.4B, C
15.5 Mass extinctions were followed by
diversification of life-forms
• At the end of the Cretaceous period, many
life-forms disappeared, including the
dinosaurs
– These mass extinctions may have been a result
of an asteroid impact or volcanic activity
?
Cretaceous
extinctions
90 million years ago
80
70
65
60
Figure 15.5
• Every mass extinction reduced the diversity
of life
– But each was followed by a rebound in diversity
– Mammals filled the void left by the dinosaurs