Transcript 17-2 Earth`s Early History

Outline 17-2: Earth's Early History
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I. Early Earth
A. The Earth is thought to be 4.5 - 5
billion years old.
1. At first a fiery ball of molten
rock
2. Eventually cooled & formed a
rocky crust
3. Water vapor condensed to
form oceans
a. Scientists think that first life
evolved in these
oceans
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17-2 Earth's Early History
II. Origins of Living Cells
A. Biogenesis does not answer the
question:
1. How did life begin on Earth?
a. No one will ever know for
certain how life began
b. Scientists have developed
theories about the origin of life
from testing scientific
hypotheses about
conditions
on early Earth
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17-2 Earth's Early History
B. How basic chemicals could form
1. All elements necessary for life were
apparently found on Earth from its
beginnings.
a. Physical & chemical processes
alone can explain the origins of ever
more complex organic chemicals on
our planet
b. This hypothesis has been tested &
confirmed many times in
laboratory experiments.
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17-2 Earth's Early History
2. Primordial soup model
a. Oparin & Haldane’s (1920s) idea:
 Earth’s early atmosphere
contained ammonia, hydrogen,
methane & water vapor
 Heat from volcanoes, sunlight and
lightning could have caused
them
to form organic
compounds
 Accumulated in a sea called the
primordial soup
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3. Miller & Urey’s Experiment (1953)
a. Tested Oparin’s hypothesis
 Put suggested gases in chamber
 Used sparks to simulate lightning
b. Results:
 Complex chemical “zoo” which
included organic compounds like
:
amino acids
fatty acids
hydrocarbons
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17-2 Earth's Early History
The First Organic Molecules
Miller and Urey’s Experiment
Mixture of gases
simulating
atmosphere of
early Earth
Spark simulating
lightning storms
Condensation
chamber
Water
vapor
Cold water cools
chamber, causing
droplets to form.
Liquid containing amino
acids and other organic
compounds
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17-2 Earth's Early History
4. Reevaluating primordial soup model
a. Early atmosphere probably did
NOT contain methane & ammonia.
It probably contained hydrogen
cyanide, carbon dioxide, carbon
monoxide, nitrogen, hydrogen
sulfide, and water.
b. Without methane & ammonia some
key biological molecules are not
made.
c. So how could organic molecules
form?
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17-2 Earth's Early History
5. Bubble model
a. Louis Lerman (1986) suggested key
processes took place within bubbles
on the ocean’s surface.
 While inside bubbles, gases get
protection from UV radiation
 Reactions could take place faster
inside bubbles (concentrated)
 Bubbles could later rise to surface
& release organic molecules into
ocean
 Energy could cause these to react
& build even more complex molecules
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C. How complex chemicals could form
1. Amino acids could have then
spontaneously linked together to form
proteins
2. RNA has been found to form
spontaneously in water
a. RNA could have been first selfreplicating molecule
b. It could also have catalyzed the
first assembly line of proteins
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17-2 Earth's Early History
The Puzzle of Life's Origin
RNA and the Origin of Life
Proteins build cell
structures and catalyze
chemical reactions
RNA nucleotides
Simple organic
molecules
RNA helps in
protein synthesis
Abiotic “stew” of
inorganic matter
RNA able to replicate itself,
synthesize proteins, and
DNA functions in
function in information
information storage
storage
and retrieval
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3. Microspheres
Cells
a. Lipids have been shown to gather
in water & form a bilayer sphere
b. Chains of amino acids will gather
into tiny vesicles called proteinoid
microspheres
c. Have selectively permeable
membranes & can store & release
energy
d. These vesicles could have been first
step toward cells
Problem: They don’t reproduce!
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Free Oxygen
III. Oldest Fossils
A. Are microfossils of unicellular
prokaryotic organisms resembling
modern bacteria
B. Found in rocks 3.5 billion years old.
C. Were anaerobic organisms.
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17-2 Earth's Early History
Free Oxygen
IV. First Oxygen
A. About 2.2 billion years ago,
photosynthetic bacteria began to pump
oxygen into the oceans.
B. Next, oxygen gas accumulated in the
atmosphere.
C. Rise of oxygen probably caused some
life forms to go extinct while others
took advantage of oxygen in new ways
(aerobic respiration)
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Free Oxygen
V. The Endosymbiotic Theory
A. Idea that eukaryotic cells formed from
a symbiosis among several different
prokaryotes.
1. Ones that used oxygen evolved into
mitochondria
2. Ones that could do photosynthesis
evolved into chloroplasts
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Origin of Eukaryotic Cells
Endosymbiotic Theory
Ancient Prokaryotes
Chloroplast
Aerobic
bacteria
Nuclear
envelope
evolving
Ancient Anaerobic
Prokaryote
Photosynthetic
bacteria
Plants and
plantlike
protists
Mitochondrion
Primitive Aerobic
Eukaryote
Primitive Photosynthetic
Eukaryote
Animals,
fungi, and
non-plantlike
protists
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17-2 Earth's Early History
Aerobic
bacteria
Origin of Eukaryotic Cells
Ancient Prokaryotes
Nuclear
envelope
evolving
Ancient Anaerobic Prokaryote
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Origin of Eukaryotic Cells
Mitochondrion
Prokaryotes that
use oxygen to
generate energyrich molecules of
ATP evolved into
mitochondria.
Primitive Aerobic Eukaryote
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17-2 Earth's Early History
Origin of Eukaryotic Cells
Prokaryotes that carried out
photosynthesis evolved into
chloroplasts.
Chloroplast
Photosynthetic
bacteria
Primitive Photosynthetic Eukaryote
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