Transcript Origins of Life

Origins of Life
Where and how did life begin?
Spontaneous Generation
• Ancient idea
• Life arises from nonlife
• In 1668 Francesco Redi
tested the idea of
spontaneous
generation with flies
and rotting meat.
• Covered flask produced
no maggots or flies.
Result: some people believed Redi, most
did not
Theory of Biogenesis,
mid-1800’s
• Only living organisms can produce other living
organisms
• Experiment conducted by Louis Pasteur using
flasks and nutrient broth
So….?
• So if Pasteur and Redi proved that
spontaneous generation was false and…
• If Pasteur proved that the theory of biogenesis
was true…
• How did the first life-forms appear?
Modern scientific thought
• Series of chemical events in Earth’s early
history
• Led from formation of simple organic
molecules to more complex organic molecules
• After a lot of study and proposed theories, we
don’t know
• But…
Primordial soup hypothesis
• Proposed by Oparin & Haldane in 1920’s
• Organic molecules in the early seas, could
have fused with gases in the early atmosphere
through energy supplied by UV rays or
lightning
• This could have supplied the chemical
substances necessary for the emergence of life
Miller & Urey experiment
• Based on primordial
soup hypothesis of
Oparin and Haldane
• Created laboratory
simulation of the
“soup” and
atmosphere
• Result was presence
of amino acids
And, so…
• Miller & Urey experiment proved that amino
acids could be formed and joined together into
chains from “soup”
• Chains broke down just as easily as they were
formed
• When amino acid chains were assembled
together in the presence of clay, they remained
stable
• Clay is readily found in the ocean, so…
Life may have started in the early oceans
• If amino acid chains remained stable in the
presence of clay, proteins could have been
formed
• Protein synthesis – accomplished by RNA
• Scientists believe RNA was present long
before DNA
• Before cells could emerge membranes must
be formed…don’t know when or how
Other possibilities…
1. Life could have originated near the deep sea
vents in the ocean
2. Meteorites could have actually brought the
first organic molecules to Earth
What was the theory that life came
from non-life?
1.
2.
3.
4.
Biogenesis
Spontaneous generation
Primordial soup
Deep sea vents
What theory stated that living organisms come
from living organisms?
1.
2.
3.
4.
Biogenesis
Spontaneous generation
Primordial soup
Deep sea vents
What did Miller & Urey accomplish?
1.
2.
3.
4.
Proved spontaneous generation was wrong
Proved biogenesis was wrong
Proved primordial soup hypothesis was right
Proved primordial soup hypothesis was
wrong
Earth’s formation
• Earth formed about 4.6 billion years ago
• Mostly a molten formation of rocks, dust and
elements under intense heat
• Gravity pulled heavier elements toward the core of
the planet
• Radiation and friction caused a huge release of heat
from the interior
• Meteorites caused additional heating as they crashed
into the Earth
Earth’s early atmosphere
• Atmosphere was mostly water vapor, sulfur dioxide,
CO2, carbon monoxide, hydrogen, hydrogen sulfide,
nitrogen, hydrogen cyanide
• Fossil records indicate intense heat and little to no
free oxygen
• Oxygen in early atmosphere bonded with iron in
igneous and metamorphic rock and was captured
there
• Most atmospheric gases were released by volcanoes
and outgassing of rock cycle and differentiation
Earth’s early atmosphere
• Eventual cooling of Earth allowed for
formation of water vapor in the form of clouds
and water forming the early oceans
• 500 million years after appearance of oceans,
we see evidence of life – 3.5 billion years ago
16
Fossil records
• Fossil – a preserved record of any organism
• Table 14.1 on page 393 Categories of Fossil
Types
• Fossils are found in sedimentary rocks – see
14.2 on pg 394 for process
• Paleontologists are scientists that study fossil
records
How do we read fossil records?
• Relative dating – determine the age of rocks
by comparing them with rocks in other layers
• Law of superposition – younger layers of rock
are deposited on older layers of rock newspapers
• Radiometric dating – uses the half-life of
radioactive isotopes to date igneous or
metamorphic rocks
How do we read fossil records?
• Uranium 238 decays to Lead 206 with a half
life of 4510 million years. Scientists compare
the amount of U238 to Pb206 to determine the
age of the sample
• Carbon 14 is used to date organic material
because it has a shorter half life
How old is the Earth?
1.
2.
3.
4.
4.6 million years
It was created in 4004 BC.
4.6 billion years
46 billion years
Earth’s early atmosphere
__________.
1. was just like the present day atmosphere.
2. had a lot of CO2 and oxygen in it.
3. would have been toxic for us to breathe.
21
Most of the early atmosphere of
Earth came from
______________.
1.
2.
3.
4.
Volcanoes and outgassing
Mars
Photosynthesis
Space
22
Relative dating of rocks
____________.
1. determines the age of rocks by comparing
them with rocks in other layers
2. states that younger layers of rock are
deposited on older layers of rock
3. uses the half-life of radioactive isotopes to
date igneous or metamorphic rocks
23
Cellular evolution
• First cells were believed to be prokaryotes, perhaps
archaea which live in extreme environments
• Archaea are autotrophs but do not photosynthesize
• Archaea do not need or produce oxygen
• Cyanobacteria, photosynthesizing prokaryotes,
appeared about 3.5 billion years ago
Cellular evolution
• Cyanobacteria, through photosynthesis,
eventually produced enough oxygen for
formation of the ozone in the stratosphere
• With presence of ozone shield, conditions
were right for appearance of eukaryotic cells
• Eukaryotes appear in fossil records about 1.8
billion years ago
Endosymbiont theory
• Eukaryotic cells appeared around 1.8 billion
years ago in fossil record
• Both mitochondria, power source for cells,
and chloroplasts, photosynthesizing center are
about the size of prokaryotic cells
• Mitochondria and chloroplasts also contain
DNA arranged in a circular pattern like in
prokaryotes
26
Endosymbiont theory
• Mitochondria and chloroplasts both
reproduce by fission (like prokaryotes)
independently of the rest of the cell
• Mitochondria and chloroplasts could have
been incorporated into eukaryotes as
organelles as parasites or undigested food
source
• Proposed in 1966 by Lynn Margulis
27
Scientific theory states that progression of
cells would have been from ____ to
_____ to _____.
1. Prokaryotes, eukaryotes,
photosynthesizing
2. Photosynthesizing, eukaryotes,
prokaryotes
3. Prokaryotes, photosynthesizing,
eukaryotes
28
Endosymbiont theory states that
______.
1. Eukaryotes incorporated prokaryotes
2. Prokaryotes incorporated eukaryotes
3. They both appeared at the same time and
the eukaryotes adapted better
4. None of the above
29