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Lesson Overview
Earth’s Early History
Lesson Overview
19.3 Earth’s Early History
Lesson Overview
Earth’s Early History
THINK ABOUT IT
How did life on Earth begin? What were the earliest forms of life? How
did life and the biosphere interact?
Origin-of-life research is a dynamic field. But even though some current
hypotheses will likely change, our understanding of other aspects of the
story is growing.
Lesson Overview
Earth’s Early History
The Mysteries of Life’s Origins
What do scientists hypothesize about early Earth and the origin of life?
Lesson Overview
Earth’s Early History
The Mysteries of Life’s Origins
What do scientists hypothesize about early Earth and the origin of life?
Earth’s early atmosphere contained little or no oxygen. It was principally
composed of carbon dioxide, water vapor, and nitrogen, with lesser
amounts of carbon monoxide, hydrogen sulfide, and hydrogen cyanide.
Lesson Overview
Earth’s Early History
The Mysteries of Life’s Origins
Pasteur 1880’s
Louis Pasteur disproved spontaneous generation with a classic experiment with a curved bottled and chicken broth
and hence any naturalistic origin of life.
Oparin (p553) 1920’s
First to propose the Earth early atmosphere did’n t contain Oxygen.It was made mostly of Carbon dioxide, water
vapor, nitogen, with lesser amount of hydrogen sulfide and hydrogen cyanide. He also proposed that
biochemical Metabolism had to evolved before the first living cell appeared and that a source of energy was
essential for that metabolism to happen. Oparin and Haldane coined the term “Primordial Soup” to the
ancient oceans of early Earth.
Miller and Urey’s (p554)1953
experiment suggested a model showing how mixtures of the organic
compounds necessary for life could have arisen from simpler compounds on a primitive Earth.
Fox (p554)
1957
Sidney Walter Fox (24 March 1912 - 10 August 1998) biochemist .Based on Miller & Urey experiment he he
proposed some hypothesis on the origins of life. Fox explored the synthesis of amino acids from inorganic
molecules, the synthesis of proteinous amino acids and amino acid polymers called "proteinoids" from
inorganic molecules and thermal energy, and created what he thought was the world's first spherical
"protocells" out of proteinoids and water. He called these protocells "microspheres" and they have now been
named "protobionts." Fox believed in spontaneous generation of life and suggested that his experiments
possessed conditions that were similar to those of primordial Earth. In his experiments, he demonstrated that
it is possible to create protein-like structures from inorganic molecules and thermal energy (abiogenesis)
Lesson Overview
Earth’s Early History
The Mysteries of Life’s Origins
Margulis (p557) 1960’s
First to explain the origin of mitochondria and chloroplasts. She also proposed that
eukaryotic flagella and cilia derived from endosymbiotic spirochetes.( cells unite with
other cells to make a mutualistic relation) film on endosymbiosis (Video youtube)
What do scientists hypothesize about early Earth and the origin of life?
“The RNA world” hypothesis proposes that RNA existed by itself before
DNA. From this simple RNA-based system, several steps could have led to
DNA-directed protein synthesis.
Lesson Overview
Earth’s Early History
The Mysteries of Life’s Origins
Geological and astronomical evidence suggests that Earth formed as
pieces of cosmic debris collided with one another. While the planet
was young, it was struck by one or more huge objects, and the entire
globe melted.
Lesson Overview
Earth’s Early History
The Mysteries of Life’s Origins
For millions of years, violent volcanic activity shook Earth’s crust.
Comets and asteroids bombarded its surface.
About 4.2 billion years ago, Earth cooled enough to allow solid rocks
to form and water to condense and fall as rain. Earth’s surface
became stable enough for permanent oceans to form.
Lesson Overview
Earth’s Early History
The Mysteries of Life’s Origins
This infant planet was very different from Earth today.
Earth’s early atmosphere contained little or no oxygen. It was principally
composed of carbon dioxide, water vapor, and nitrogen, with
lesser amounts of carbon monoxide, hydrogen sulfide, and hydrogen cyanide.
Because of the gases in the atmosphere, the sky was probably pinkishorange.
Because they contained lots of dissolved iron, the oceans were probably
brown.
Lesson Overview
Earth’s Early History
The First Organic Molecules
In 1953, chemists Stanley Miller and
Harold Urey tried recreating conditions
on early Earth to test the hypothesis that
complexe organic molecules could
have been formed from simpler
inorganic atmospheric molecules such
as CO2 , N2 and H2O
They filled a sterile flask with water, to
simulate the ocean (“primordial soup”),
and boiled it.
Mille/Urey animation
Lesson Overview
Earth’s Early History
The First Organic Molecules
To the water vapor, they added
methane, ammonia, and
hydrogen, to simulate what they
thought had been the composition
of Earth’s early atmosphere.
They passed the gases through
electrodes, to simulate lightning.
Lesson Overview
Earth’s Early History
The First Organic Molecules
Next, they passed the gases
through a condensation chamber,
where cold water cooled them,
causing drops to form. The liquid
continued to circulate through the
experimental apparatus for a
week.
After a week, they had produced
21 amino acids—building blocks
of proteins.
Lesson Overview
Earth’s Early History
The First Organic Molecules
Miller and Urey’s experiment
suggested how mixtures of the
organic compounds necessary
for life could have arisen from
simpler compounds on a primitive
Earth.
We now know that Miller and
Urey’s ideas on the composition
of the early atmosphere were
incorrect. But new experiments
based on current ideas of the
early atmosphere have produced
similar results.
Lesson Overview
Earth’s Early History
Formation of Proteinoid Microspheres (FOX)
Geological evidence suggests that during the Archean Eon, 200 to 300
million years after Earth cooled enough to carry liquid water, cells
similar to bacteria were common. How did these cells originate?
Large organic molecules made of amino acids polymers under heat
energy, form tiny bubbles called proteinoid microspheres under
certain conditions.
Microspheres are not cells, but they have some characteristics of living
systems such as : selectively permeable through which water
molecules and some gas can pass.
Lesson Overview
Earth’s Early History
Formation of Microspheres
Like cells, microspheres have selectively permeable membranes
through which water molecules can pass.
Microspheres also have a simple means of storing and releasing
energy.
Several hypotheses suggest that structures similar to proteinoid
microspheres acquired the characteristics of living cells as early as 3.8
billion years ago.
Lesson Overview
Earth’s Early History
Evolution of RNA and DNA
Cells are controlled by information stored in DNA, which is transcribed
into RNA and then translated into proteins.
The “RNA world” hypothesis about the origin of life suggests that RNA
evolved before DNA. From this simple RNA-based system, several
steps could have led to DNA-directed protein synthesis.
Lesson Overview
Earth’s Early History
Evolution of RNA and DNA
A number of experiments that simulated conditions on early Earth
suggest that small sequences of RNA could have formed from simpler
molecules.
Under the right conditions, some RNA sequences help DNA replicate.
Other RNA sequences process messenger RNA after transcription. Still
other RNA sequences catalyze chemical reactions. Some RNA
molecules even grow and replicate on their own.
Lesson Overview
Earth’s Early History
Evolution(by natural selection) of RNA and DNA
1) RNA world Hypothesis Biochemical completion Youtube Video
2) Orgin of Life with RNA
One hypothesis about the origin of life suggests that RNA evolved before
DNA.
Lesson Overview
Earth’s Early History
Production of Free Oxygen
Microscopic fossils, or microfossils, of prokaryotes that resemble
bacteria have been found in Archean rocks more than 3.5 billion years
old.
Those first life forms evolved in the absence of oxygen gas (O2)
because at that time was rare . Oxygen atoms may be found in
compound such as water (H2O) and carbon dioxide (Co2). Oxygen was
present in Earth’s atmosphere in very little amout . It is formed in
stars and the third-most abundant element in the universe ;hence, Oxygen
gas could have been “imported” though crashing comets and meteorites like
some of the water and carbon dioxide gas.
Lesson Overview
Earth’s Early History
Production of Free Oxygen
During the early Proterozoic Eon, photosynthetic bacteria became
common. By 2.2 billion years ago, these organisms were producing
oxygen.
Lesson Overview
Earth’s Early History
Production of Free Oxygen
At first, the oxygen combined with iron in the oceans, producing iron
oxide, or rust.
Iron oxide, which is not soluble in water, sank to the ocean floor and
formed great bands of iron that are the source of most iron ore mined
today.
Without iron, the oceans changed color from brown to blue-green.
Lesson Overview
Earth’s Early History
Production of Free Oxygen
Next, oxygen gas began to accumulate in the atmosphere. (You tube
video from cell to advanced multicellular organisms , Cambrian
explosion etc… 10”)
The ozone layer began to form, and the
skies turned their present shade of blue.
Over several hundred million years, oxygen concentrations rose until
they reached today’s levels
Lesson Overview
Earth’s Early History
Production of Free Oxygen
Many scientists think that Earth’s early atmosphere may have been
similar to the gases released by a volcano today.
The graphs show the composition of the atmosphere today and the
composition of gases released by a volcano.
Lesson Overview
Earth’s Early History
Production of Free Oxygen
To the first cells, which evolved in the absence of oxygen, this reactive
oxygen gas was a deadly poison that drove this type of early life to
extinction.
Some organisms, however, evolved new metabolic pathways that used
oxygen for respiration and also evolved ways to protect themselves
from oxygen’s powerful reactive abilities.
Lesson Overview
Earth’s Early History
Origin of Eukaryotic Cells
What theory explains the origin of eukaryotic cells?
Lesson Overview
Earth’s Early History
Origin of Eukaryotic Cells
What theory explains the origin of eukaryotic cells?
The endosymbiotic theory proposes that a symbiotic relationship evolved
over time, between primitive eukaryotic cells and the prokaryotic cells
within them.
Lesson Overview
Earth’s Early History
Origin of Eukaryotic Cells
One of the most important events in the history of life was the evolution of
eukaryotic cells from prokaryotic cells.
Eukaryotic cells have nuclei, but prokaryotic cells do not.
Eukaryotic cells also have complex organelles. Virtually all eukaryotes
have mitochondria, and both plants and algae also have chloroplasts.
1.
Endosymbiosis Animation
Lesson Overview
Earth’s Early History
Endosymbiotic Theory
It is believed that about 2 billion years ago, some ancient prokaryotes
began evolving internal cell membranes. These prokaryotes were the
ancestors of eukaryotic organisms.
According to endosymbiotic theory, prokaryotic cells entered those
ancestral eukaryotes. The small prokaryotes began living inside the
larger cells.
Lesson Overview
Earth’s Early History
Endosymbiotic Theory
Over time a symbiotic relationship evolved between a community of 3
kind prokaryotic cells.
1. Small Ancient photosynthetic bacteria(prokaryote)
2. Small Ancient aerobic bacteria(prokaryote)
3. Larger Ancient Anaerobic prokaryote
Lesson Overview
Earth’s Early History
Endosymbiotic Theory
The endosymbiotic theory was proposed more than a century ago.
At that time, microscopists saw that the membranes of mitochondria
and chloroplasts resembled the cell membranes of free-living
prokaryotes.
This First observation led to two related hypotheses.
Lesson Overview
Earth’s Early History
Endosymbiotic Theory
1) hypothesis proposes that mitochondria evolved from endosymbiotic
prokaryotes that were able to metabolize oxygen to generate energyrich ATP molecules.
Without this ability to metabolize oxygen, cells would have been killed
by the free oxygen in the atmosphere.
Lesson Overview
Earth’s Early History
Endosymbiotic Theory
The Second hypothesis proposes that chloroplasts evolved from
endosymbiotic prokaryotes that had the ability to photosynthesize.
Over time, these photosynthetic prokaryotes evolved within eukaryotic
cells into the chloroplasts of plants and algae.
Lesson Overview
Earth’s Early History
5 Modern Evidences for Endosymbiosis hypothesis
1) During the 1960s, Lynn Margulis of Boston University noted that
mitochondria and chloroplasts contain DNA similar to bacterial DNA.
2)She also noted that mitochondria and chloroplasts have ribosomes
whose size and structure closely resemble those of bacteria.
3)In addition, she found that mitochondria and chloroplasts, like
bacteria, reproduce by binary
divide by mitosis.
fission when cells containing them
4) mitochondria and chloroplasts had cell
membrane like bacteria
These similarities provide strong evidence of a common ancestry
between free-living bacteria and the organelles of living eukaryotic cells.
5) mitochondria and chloroplasts are the same size as bacteria
animation of Endosymbiosis
Lesson Overview
Earth’s Early History
Sexual Reproduction and Multicellularity
What is the evolutionary significance of sexual reproduction?
Lesson Overview
Earth’s Early History
Sexual Reproduction and Multicellularity
What is the evolutionary significance of sexual reproduction?
The development of sexual reproduction sped up evolutionary change
because sexual reproduction increases genetic variation.
Lesson Overview
Earth’s Early History
Significance of Sexual Reproduction
When prokaryotes reproduce asexually, they duplicate their genetic
material and pass it on to daughter cells.
This process is efficient, but it yields daughter cells whose genomes
duplicate their parent’s genome.
Genetic variation is basically restricted to mutations in DNA.
Lesson Overview
Summary
Earth’s Early History
1) Oparin (1920’s) proposed that Metabolism appeared first, before life arose, using molecules from
an anaerobic atmosphere. Simple inorganic molecules were transformed into complex biomacromolecules using lighting as the source of energy.
2) Formation organic aggregate first and then of Proteonoid microsphere with selectively permeable
membrane
3) .”RNA world". From a lot of different models, Natural selection select the “fittest RNA”. RNA is a
simpler molecule that later helped the more complex DNA to translate its genetic code into
Proteins. RNA had to appear first.
4) 4.B.Y.A DNA a product of RNA mutations. The earliest cells absorbed energy and food
(heterotrophs)from the surrounding environment. They used fermentation, the breakdown of
more complex compounds into less complex compounds with less energy, and used the energy so
liberated to grow and reproduce. Fermentation can only occur in an anaerobic = anoxygenic
(oxygen-free) environment
5) 3.8 B.Y.A Chemo-autotrophs (anoxygenic) appeared >Archaea using Hydrogen sulfide as a
source of energy.DNA might have been present
6) 2.2 B.Y.A Photoautotrophs prokaryotes> first appearance of Oxygen in the atmosphere , a
byproduct of photosynthesis when H2o(Hydrogen Oxide) is split> future chloroplast
7) Heterotroph prokaryotes metabolize oxygen and the carbohydrate produced by the photoautotrophs> future mitochondria
8) 2. B.Y.A Endosymbiosis hypothesis : mitochondria & chloroplast appear
9) 600 m. y. a :In the Ocean only. Simple Multicellular organism reproduction by mitosis
10) 550 m y. a :Appearance of collagen, advanced multicellular and sexual reproduction which
bring about greater variation> adaptive radiation> “Cambrian explosion”