Origins of Life PowerPoint
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Origins of Life on Earth
Where did life come from?
Early Ideas
Spontaneous Generation
Believed life “arose” from nonliving objects.
Mice came from piles of grain
Bees were produced from carcasses of cattle
Maggots came from rotting meat
Lice from sweat
Francesco Redi
1668
Hypothesized maggots arose from eggs that
were to small to see with the naked eye.
Tested his hypothesis by placing meat in
several jars.
½ open to air directly
½ covered with gauze
Gauze covered were exposed to air
Maggots formed in open jars
No maggots formed in gauze covered jars
DISPROVED SPONTANEOUS GENERATION!!!
Francesco Redi
Francesco Redi
A
B
C
John Needham
o
Attacked Redi’s conclusions
o
Sealed gravy in a bottle
o
Heated the bottle to kill the living organisms in it.
o
After several days, examined the bottle under a microscope
o
Found it swarming with microscopic organisms
o
Concluded the microorganisms “could only have come from
the juice of the gravy.”
Lazzaro Spallanzani
» Considered “Spontaneous Generation”
» Knew of Redi’s & Needham’s experiments
» Believed Needham was wrong.
» Thought Needham didn’t kill bacteria by heating.
Lazzaro Spallanzani
» Prepared identical gravy to Needham
» Put ½ the gravy into one jar, the other ½ into another jar
» Boiled both jars
» Sealed one, left the other open to the air
» After a few days, the open one was teeming with life
» The sealed jar had no living things in it.
Lazzaro Spallanzani
» Spallanzani concluded that the microorganisms did not come from the
gravy, but entered the jar through the air (Air was a Vital Force).
» People still believed that Spallanzani’s work was flawed.
» They said that air was necessary for spontaneous generation.
» By sealing the jar, the air was kept out.
Louis Pasteur
Finally disproved “Spontaneous Generation”
Placed nutrient broth similar to Needham and
Spallanzani into some flasks with long curving necks
Boiled the flasks thoroughly
Waited for one year
1864
Louis Pasteur
Louis Pasteur
No microorganisms formed – even though open to the air
After a year, he broke the neck of some of the flasks
All developed microorganisms
Conclusion: Life from Life
Where did life come from?
That’s the million dollar question
Early Ideas
First atmosphere contained
Water vapor (H2O)
Carbon Monoxide (CO)
Nitrogen (N2)
Hydrogen Sulfide (H2S)
Hydrogen Cyanide (HCN)
No free oxygen
Could not support life as we know it
Geological evidence supports this because rocks from this
period contain no iron oxide (Rust) or other compounds
that require free oxygen to form
The Molecules of Life
Stanley Miller and Harold Urey
Miller recreated what he thought might have been earth’s
earliest atmospheres by mixing
-ammonia
-water
-hydrogen
in a flask & exposed the flask to electric sparks (Lightning)
Miller-Urey
Organic Soup?
In a few days, “Organic Soup” – complex molecules
- urea
- acetic acid
- lactic acid
- several amino acids
- ATP
- Nitrogenous base adenine
Complex Molecules of Life
Formation of Complex Molecules
Russian Alexander Oparin and American Sidney Fox showed
that the organic soup that formed in the oceans could form
other compounds
In the absence of Oxygen, amino acids tend to link together
to form chains.
What do chains of amino
acids form?
Proteins
Protolife
Others compounds form carbohydrates,
alcohols, and lipids
Collections of molecules like this tend to
gather into round droplets
Some of these droplets grow and even
reproduce
Some break down glucose
These droplets are called “proto-life” because
they are not “alive”, but have begun to
perform tasks necessary for life
Protolife to Cells
DNA & RNA must have somehow been
created molecules can replicate
First Cells
Several hypotheses
Some believe first cells came from a
shallow pool containing organic soup
when the organic soup is dried, lipids
form spheres around small DNA
molecules
Given time, a form of DNA that is
capable of replicating could have arisen
First Cells
G. Cairns-Smith and J. Bernal:
noted attractive forces concentrate
amino acids, DNA and RNA onto clay
crystals
Held together, these may have formed
lengths of proteins and DNA
First Cells
Several scientists believe the first cells formed
near volcanic vents deep in the ocean
Very high temperatures
Lots of sulfur compounds
Assortment of chemicals
Strong currents to mix them
Deposits of clay
First Cells
scientists who duplicated these conditions
observed the spontaneous synthesis of amino
acids and RNA
First True Cells
First cells were prokaryotes
Resembled some bacteria
Heterotrophs
Anaerobes (can live without oxygen)
Photosynthesis
Heterotrophic cells could have survived for a
long time without difficulty finding “Food”
Sooner or later, the food would run out.
Complex molecules in the organic soup would
be depleted.
Some organisms would have to develop
complex molecules from simple ones
Natural selection would favor ability to
harness outside energy source
Stromatolites
First cells probably used Hydrogen
Sulfide instead of Water
Successful, spread rapidly and common
3.4 million years ago
Grew in mats called Stromatolites
Still can find stromatolites in special
habitats, but fossils have been found all
over the world
Stromatolites
Life from Non-life
We said that life did not come from
non-life, how did life start?
Earth then … and now
Earth of today is very different from earth of
billions of years ago.
No oxygen to break down organic compounds
Today, such compounds cannot remain intact
in the natural world long enough to give
another start to life
Road to Modern Organisms
2.2 billion years ago, a more modern form of
photosynthesis evolved.
The use of H2O instead of H2S
Deadly gas?
This put out deadly gas …
OXYGEN!
Effects of photosynthesis
Over the next 500 Million years, the
waste product given off by some
organisms changed the earth from an
anaerobic planet to an aerobic planet.
Nearly 1/5 Oxygen
Oxygen
Because oxygen was toxic to anaerobes, they
had to survive in areas with no oxygen such
as deep in mud, or other places oxygen does
not reach.
Oxygen was beneficial to those that survived
Oxygen that reached the upper atmosphere
was changed from O2 to O3 (Ozone) that
shielded earth from much of the UV light
from the sun.
Aerobic Metabolism
Evolution of Aerobic Metabolism
organisms evolved that used Oxygen in
their metabolic pathways (remember
chapter 6)
18X more efficient than anaerobic
respiration
Eukaryotes
Eukaryotic cells
between 1.4 and 1.6 billion years ago,
the first eukaryotic cells evolved.
Endosymbiont Hypothesis
Endosymbiont Hypothesis
Lynn Margulis
Noticed Chloroplasts and Mitochondria both
had their own DNA
Circular piece of DNA similar to bacterial
plasmid
Hypothesized that organelles were originally
prokaryotes that somehow ended up inside
another cell
Reproduction
Sexual reproduction
Sexual reproduction was an extremely large
step towards evolution
Asexual reproduction makes exact copies of
cells. Only chance of change is by mutation.
Sexual reproduction shuffles genetic material
every time.
offspring never are exactly like parents
Multicellular
A few hundred million years after
evolution of sexual reproduction –
multicellular life
Great adaptive radiation
Life was on its way.