Origins of Life on Earth

Where did life come from?

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

Francesco Redi

A B C

Francesco Redi

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

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)

Miller-UreyMiller-Urey

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.

What do chains of amino acids form?

Proteins

What do chains of amino acids form?

Proteins

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

StromatolitesStromatolites

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

Deadly gas?Deadly gas?

This put out deadly gas …OXYGEN!

This put out deadly gas …OXYGEN!

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

MulticellularMulticellular

A few hundred million years after evolution of sexual reproduction – multicellular life

Great adaptive radiation Life was on its way.

A few hundred million years after evolution of sexual reproduction – multicellular life

Great adaptive radiation Life was on its way.