origins of life on earth where did life come from?
TRANSCRIPT
Early Ideas 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
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 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!!!
1668
John NeedhamJohn Needhamo 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.”
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 PasteurLouis 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
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?
Where did life come from?
That’s the million dollar question
That’s the million dollar question
Early Ideas 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
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 LifeThe 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)
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)
Organic Soup?Organic Soup?Organic Soup?Organic Soup?
In a few days, “Organic Soup” – complex molecules
- urea - acetic acid - lactic acid - several amino acids - ATP - Nitrogenous base adenine
In a few days, “Organic Soup” – complex molecules
- urea - acetic acid - lactic acid - several amino acids - ATP - Nitrogenous base adenine
Complex Molecules of Life 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.
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.
ProtolifeProtolifeOthers compounds form carbohydrates,
alcohols, and lipidsCollections of molecules like this tend to
gather into round dropletsSome of these droplets grow and even
reproduceSome break down glucoseThese droplets are called “proto-life”
because they are not “alive”, but have begun to perform tasks necessary for life
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 glucoseThese droplets are called “proto-life”
because they are not “alive”, but have begun to perform tasks necessary for life
Protolife to CellsProtolife to Cells
DNA & RNA must have somehow been created molecules can replicate
DNA & RNA must have somehow been created molecules can replicate
First CellsFirst Cells
Several hypothesesSome believe first cells came from a
shallow pool containing organic soupwhen 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
Several hypothesesSome believe first cells came from a
shallow pool containing organic soupwhen 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 CellsFirst 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
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 CellsFirst Cells
Several scientists believe the first cells formed near volcanic vents deep in the ocean
Very high temperaturesLots of sulfur compoundsAssortment of chemicalsStrong currents to mix themDeposits of clay
Several scientists believe the first cells formed near volcanic vents deep in the ocean
Very high temperaturesLots of sulfur compoundsAssortment of chemicalsStrong currents to mix themDeposits of clay
First CellsFirst Cells
scientists who duplicated these conditions observed the spontaneous synthesis of amino acids and RNA
First True CellsFirst cells were prokaryotesResembled some bacteriaHeterotrophsAnaerobes (can live without oxygen)
scientists who duplicated these conditions observed the spontaneous synthesis of amino acids and RNA
First True CellsFirst cells were prokaryotesResembled some bacteriaHeterotrophsAnaerobes (can live without oxygen)
PhotosynthesisPhotosynthesis
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
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
StromatolitesStromatolites
First cells probably used Hydrogen Sulfide instead of Water
Successful, spread rapidly and common 3.4 million years ago
Grew in mats called StromatolitesStill can find stromatolites in special
habitats, but fossils have been found all over the world
First cells probably used Hydrogen Sulfide instead of Water
Successful, spread rapidly and common 3.4 million years ago
Grew in mats called StromatolitesStill can find stromatolites in special
habitats, but fossils have been found all over the world
Life from Non-lifeLife from Non-life
We said that life did not come from non-life, how did life start?
We said that life did not come from non-life, how did life start?
Earth then … and nowEarth then … and nowEarth of today is very different from
earth of billions of years ago.No oxygen to break down organic
compoundsToday, such compounds cannot remain
intact in the natural world long enough to give another start to life
Road to Modern Organisms2.2 billion years ago, a more modern
form of photosynthesis evolved. The use of H2O instead of H2S
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 Organisms2.2 billion years ago, a more modern
form of photosynthesis evolved. The use of H2O instead of H2S
Effects of photosynthesisEffects 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
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 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.
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 MetabolismAerobic Metabolism
Evolution of Aerobic Metabolismorganisms evolved that used
Oxygen in their metabolic pathways (remember chapter 6)
18X more efficient than anaerobic respiration
Evolution of Aerobic Metabolismorganisms evolved that used
Oxygen in their metabolic pathways (remember chapter 6)
18X more efficient than anaerobic respiration
Eukaryotes Eukaryotes
Eukaryotic cellsbetween 1.4 and 1.6 billion years
ago, the first eukaryotic cells evolved.
Eukaryotic cellsbetween 1.4 and 1.6 billion years
ago, the first eukaryotic cells evolved.
Endosymbiont HypothesisEndosymbiont Hypothesis
Endosymbiont HypothesisLynn 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
Endosymbiont HypothesisLynn 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
ReproductionReproduction
Sexual reproductionSexual reproduction was an extremely
large step towards evolutionAsexual 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
Sexual reproductionSexual reproduction was an extremely
large step towards evolutionAsexual 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