Cosmos (1980): Season 1, Episode 2 - One Voice in the Cosmic Fugue - full transcript
Carl Sagan examines the origin, development, and complexity of life on Earth and speculates on the possibility of life developing elsewhere in the universe.
SAGAN: All my life I've wondered
about life beyond the Earth.
On those countless other planets
that we think circle other suns...
...is there also life?
Might the beings of other
worlds resemble us...
...or would they be
What would they be made of?
In the vast Milky Way galaxy...
...how common is what we call life?
The nature of life on Earth...
...and the quest for life elsewhere...
...are the two sides
of the same question.
The search for who we are.
All living things on Earth
are made of organic molecules...
...a complex microscopic
...built around atoms of carbon.
In the great dark between the stars...
...there also are organic molecules...
...in immense clouds of gas and dust.
Inside such clouds...
...there are batches
of new worlds just forming.
Their surfaces are very likely
covered with organic molecules.
These molecules almost certainly
are not made by life...
are the stuff of life.
On suitable worlds,
they may lead to life.
Organic matter is abundant
throughout the cosmos...
...produced by the same chemistry
Perhaps, given enough time...
...the origin and evolution of life
is inevitable on every clement world.
There will surely be some planets
too hostile for life.
it may arise and die out...
...or never evolve
beyond its simplest forms.
And on some small
fraction of worlds...
...there may develop intelligences
...more advanced than ours.
All life on our planet
is closely related.
We have a common organic chemistry
and a common evolutionary heritage.
And so our biologists
are profoundly limited.
They study a single biology...
...one lonely theme
in the music of life.
Is it the only voice
for thousands of light years...
...or is there a cosmic fugue,
a billion different voices...
...playing the life music
of the galaxy?
This blue world is where we grew up.
There was once a time before life.
Our planet is now
burgeoning with life.
How did it come about?
How were organic molecules
How did life evolve
to produce beings...
...as elaborate and complex as we...
...able to explore the mystery
of our own origins?
Let me tell you a story
about one little phrase...
...in the music of life on Earth.
In the history of humans...
...in the 12th century...
...Japan was ruled by a clan
of warriors called the Heike.
The nominal leader of the Heike,
the emperor of Japan...
...was a 7-year-old boy
His guardian was his grandmother,
the Lady Nii.
The Heike were engaged
in a long and bloody war...
...with another Samurai clan,
a superior ancestral claim...
...to the imperial throne.
Their decisive encounter
occurred at Dannoura...
...in the Japanese Inland Sea
on April 24...
...in the year 1 185.
The Heike were badly outnumbered
With their cause clearly lost...
...the surviving Heike warriors threw
themselves into the sea and drowned.
The emperor's grandmother,
the Lady Nii...
...resolved that they would not
be captured by the enemy.
What happened next is related
in "The Tale of the Heike":
"The young emperor asked the Lady Nii,
'Where are you to take me?'
She turned to the youthful sovereign
with tears streaming down her cheeks...
...and comforted him.
Blinded with tears...
...the child sovereign put his
beautiful small hands together.
He turned first to the east...
...to say farewell
to the god of Ise...
...and then to the west...
...to recite a prayer
to the Amida Buddha.
The Lady Nii...
...took him in her arms,
and with the words:
'In the depths of the ocean
is our capital'...
...sank with him at last
beneath the waves."
The destruction of the Heike
battle fleet at Dannoura...
...marked the end of the clan's
The Heike all but vanished
Only 43 Heike survived, all women.
These former ladies-in-waiting
of the Imperial Court...
...were reduced to selling flowers
and other favors...
...to the fishermen near
the scene of the battle.
These women and their offspring
by the fishermen...
...established a festival
to commemorate the battle.
To this day, every year,
on the 24th of April...
...their descendants proceed
to the Akama shrine...
...which contains the mausoleum...
...of the drowned
7-year-old emperor, Antoku.
There, they conduct a ceremony
...for the life and death
of the Heike warriors.
But there is a strange
postscript to this story:
The fishermen say...
...that the Heike samurai
wander the bottom of the Inland Sea...
...in the form of crabs.
There are crabs here which have
curious markings on their backs.
Patterns which resemble
a human face...
...with the aggressive scowl
of a samurai warrior...
...from medieval Japan.
These Heike crabs, when caught,
are not eaten.
They are thrown back into the sea...
of the doleful events...
...of the battle of Dannoura.
This legend raises a lovely problem:
How does it come about that the face
of a warrior...
...is cut on the carapace of
a Japanese crab? How could it be?
The answer seems to be
that humans made this face.
Like many other features,
the patterns on the back...
...or carapace of this crab
But among crabs, as among humans,
there are different hereditary lines.
Now, suppose purely by chance...
...among the distant ancestors
of this crab...
...there came to be one which looked
just a little bit like a human face.
Long before the battle, fishermen
may have been reluctant...
...to eat a crab with a human face.
In throwing it back into the sea...
...they were setting into motion
a process of selection.
If you're a crab and your carapace
is just ordinary...
...the humans are gonna eat you.
But if it looks a little bit
like a face...
...they'll throw you back and you
can have lots of baby crabs...
...that all look just like you.
As many generations passed...
...of crabs and fisher-folk alike...
...the crabs with patterns that
looked most like a samurai face...
Until eventually, there was produced
not just a human face...
...not just a Japanese face...
...but the face of a samurai warrior.
All this has nothing to do
with what the crabs might want.
Selection is imposed from the outside.
The more you look like a samurai,
the better your chances of survival.
Eventually, there are a lot of crabs
that look like samurai warriors.
This process is called
In the case of the Heike crab,
it was effected...
...more or less unconsciously
by the fishermen...
...and certainly without any serious
contemplation by the crabs.
Humans, for thousands of years...
...have deliberately selected...
and animals shall live.
by farm and domestic animals...
Where do they come from? Were they
once free-living in the wild...
...and then induced to adopt some
less strenuous life on the farm?
They are, almost all of them,
made by us.
The essence of artificial selection
for a horse or a cow...
...a grain of rice
or a Heike crab, is this:
Many characteristics are inherited.
They breed true.
Humans encourage the reproduction
of some varieties...
the reproduction of others.
The variety selected for,
eventually becomes abundant.
The variety selected against,
becomes rare, maybe extinct.
But if artificial selection
makes such changes...
...in only a few thousand years...
...what must natural selection...
...working for billions of years,
be capable of?
...is all the beauty and diversity
in the biological world.
That life evolved over
the ages is clear...
...from the changes we've made
in the beasts and vegetables...
...but also from
the record in the rocks.
The fossil evidence speaks
to us unambiguously...
...of creatures that were once
present in enormous numbers...
...and that have now vanished utterly.
There are more species that have
become extinct than exist today.
They are the terminated
experiments in evolution.
These guys, the trilobites,
appeared 600 million years ago.
They were around
for 300 million years.
They're all gone. There's none left.
But in those old rocks, there are
no fossils of people or cattle.
We've evolved only recently.
Evolution is a fact, not a theory.
It really happened.
That the mechanism of evolution is
natural selection was the discovery...
...of Charles Darwin
and Alfred Russel Wallace.
Here's how it works:
Nature is prolific.
There are many more creatures that
are born than can possibly survive.
So those varieties which are,
by accident, less well adapted...
...don't survive, or at least
they leave fewer offspring.
Now, mutations, sudden
changes in heredity...
...are passed on. They breed true.
The environment selects the occasional
mutations which enhance survival.
The resulting series of slow changes
in the nature of living beings...
...is the origin of new species.
Many people were scandalized...
...by the ideas of evolution
and natural selection.
Our ancestors looked at...
and the beauty of life...
...and saw evidence
for a great designer.
The simplest organism
is a far more complex machine...
...than the finest pocket watch.
And yet, pocket watches don't
...or evolve in slow
stages on their own...
...from say, grandfather clocks.
A watch implies a watchmaker.
There seemed to be no way atoms
could spontaneously fall together...
...and create, say...
The idea of a designer...
...is an appealing and altogether human
explanation of the biological world.
But as Darwin and Wallace showed...
...there's another way...
and far more compelling.
Natural selection, which makes
the music of life more beautiful...
...as the eons pass.
To understand the passage
of the eons...
...we have compressed all of time
into a single cosmic year...
...with the big bang on January first.
Every month here represents
a little over a billion years.
The Earth didn't form until
the cosmic year was two-thirds over.
Our understanding of the history
of life is very recent...
...occupying only the last few
seconds of December 31...
...that small white spot at bottom
right in the cosmic calendar.
What happened on Earth may be
more or less typical...
...of the evolution of life
on many worlds.
But in its details...
...the story of life on Earth...
...is probably unique
in all the Milky Way galaxy.
The secrets of evolution
are time and death.
Time for the slow accumulation
of favorable mutations...
...and death to make room
for new species.
Life on Earth arose in September
of the cosmic calendar...
...when our world, still battered and
cratered from its violent origin...
...may have looked
a little like the moon.
The Earth is about four and a half
billion years old.
In the cosmic calendar...
...it condensed out of interstellar
gas and dust...
...around September 1 4.
We know from the fossil record
that life originated soon after...
...maybe around September 25,
something like that...
...probably in the ponds and oceans
of the primitive Earth.
The first living things were not
as complex as a one-celled organism...
...which is already a highly
sophisticated form of life.
No, the first stirrings
of life were much more humble...
...and happened on the molecular level.
In those early days, lightning
and ultraviolet light from the sun...
...were breaking apart hydrogen-rich
molecules in the atmosphere.
The fragments of the molecules
were spontaneously recombining...
...into more and more
The products of this early
chemistry dissolved in the oceans...
...forming a kind of organic soup...
...of gradually increasing complexity.
Until one day, quite by accident...
...a molecule arose that was able
to make crude copies of itself...
...using as building blocks
the other molecules in the soup.
This was the ancestor of DNA...
...the master molecule
of life on Earth.
It's made of four different
parts, called nucleotides...
...which constitute the four letters
of the genetic code...
...the language of heredity.
Each of the nucleotides,
the rungs on the DNA ladder...
...are a different color
in this model.
The instructions are different
for different organisms.
That's why organisms
Now, a mutation is a change
of a nucleotide...
of the genetic instructions.
Most mutations spell genetic
nonsense since they're random.
They harm the next generation.
But a very few, by accident...
...make better sense than the
original codes, and aid evolution.
DNA is about a billion
...than we see it here.
Each of those things that looks
like a piece of fruit is an atom.
Without the tools of science...
...the machinery of life
would be invisible.
Four billion years ago...
...the ancestors of DNA competed
for molecular building blocks...
...and left crude copies
There were no predators;
the stuff of life was everywhere.
The oceans and murky pools
that filled the craters...
...were, for these molecules,
a Garden of Eden.
With reproduction, mutation
and natural selection...
...the evolution of living
molecules was well underway.
Varieties with specialized
functions joined together...
...making a collective.
The first cell.
The organic soup eventually
ate itself up.
But by this time, plants had evolved,
able to use sunlight...
...to make their own building blocks.
They turned the waters green.
The first multi-cellular organisms.
Equally important was the invention,
not made until early November...
...of sex. It was stumbled upon
by the microbes.
By December 1, green plants
had released copious amounts...
...of oxygen and nitrogen
into the atmosphere.
The sky is made by life.
Then, suddenly, on December 1 5...
...there was an enormous proliferation
of new life forms...
...an event called
the "Cambrian Explosion."
We know from fossils that life arose
shortly after the Earth formed...
...suggesting that the origin
of life might be...
...an inevitable chemical process
on countless Earth-like planets...
...throughout the cosmos.
But on the Earth, in nearly 4 billion
years, life advanced no further...
So maybe more complex forms of life
are harder to evolve...
...harder even than the origin
of life itself.
If this is right, the planets
of the galaxy...
...might be filled
...but big beasts and vegetables
and thinking beings...
...might be comparatively rare.
By December 18, there were vast
herds of trilobites...
...foraging on the ocean bottom...
...and squid-like creatures with
We know enough to sketch in a few
of the subsequent details.
The first fish and the first
vertebrates appeared on December 19.
Plants began to colonize the land
on December 20.
The first winged insects fluttered by
on December 22.
On this date also, there were
the first amphibians...
like the lungfish...
...able to survive both on land
and in water.
Our direct ancestors were now
leaving the oceans behind.
The first trees and the first reptiles
evolved on December 23:
Two amazing evolutionary developments.
We are descended
from some of those reptiles.
The dinosaurs appeared
on Christmas Eve.
There were many different
kinds of dinosaurs.
The Earth was once their planet.
Many stood upright and had
some fair intelligence.
Great lizards crashed and thundered
through the steaming jungles.
Unnoticed by the dinosaurs,
a new creature...
...whose young were born live
...was making its timid debut.
The first mammals emerged
on December 26...
...the first birds
on the following day.
But the dinosaurs still
dominated the planet.
Then suddenly, without warning,
all over the planet at once...
...the dinosaurs died.
The cause is unknown,
but the lesson is clear:
Even 160 million years on a planet
is no guarantee of survival.
The dinosaurs perished
around the time of the first flower.
On December 30, the first creatures...
...who looked even a little bit human,
...accompanied by a spectacular increase
in the size of their brains.
And then, on the evening
of the last day of the last month...
...only a few million years ago...
...the first true humans took
their place on the cosmic calendar.
The written record of history...
...occupies only the last 10 seconds
of the cosmic year.
Now, let's take a closer look
at who our ancestors were.
A simple chemical circumstance
led to a great moment...
...in the history of our planet.
There were many molecules
in the primordial soup.
Some were attracted to water on one
side and repelled by it on the other.
This drove them together...
...into a tiny enclosed
...like a soap bubble,
which protected the interior.
Within the bubble,
the ancestors of DNA found a home...
...and the first cell arose.
It took hundreds of millions of years
for tiny plants to evolve...
...giving off oxygen.
But that branch didn't lead to us.
Bacteria that could breathe oxygen
took over a billion years to evolve.
From a naked nucleus, a cell
developed with a nucleus inside.
Some of these amoeba-like forms
led eventually to plants.
Others produced colonies...
...with inside and outside cells
performing different functions.
...a polyp attached
to the ocean floor...
...filtering food from the water...
...and evolving little tentacles...
...to direct food
into a primitive mouth.
This humble ancestor of ours
...to spiny-skinned armored animals
with internal organs...
...including our cousin, the starfish.
But we don't come from starfish.
About 550 million years ago...
evolved gill slits...
...which were more efficient
at straining food particles.
One evolutionary branch
led to acorn worms.
Another led to a creature which
swam freely in the larval stage...
...but, as an adult, was still
firmly anchored to the ocean floor.
Some became living hollow tubes.
But others retained the larval forms
throughout the life cycle...
...and became free-swimming adults
with something like a backbone.
Our ancestors now...
...500 million years ago,
were jawless filter-feeding fish...
...a little like lampreys.
Gradually, those tiny fish...
...evolved eyes and jaws.
Fish then began to eat one another...
...if you could swim fast,
If you had jaws to eat with, you could
use your gills to breathe in the water.
This is the way modern fish arose.
During the summer,
swamps and lakes dried up.
Some fish evolved a primitive lung
to breathe air until the rains came.
Their brains were getting bigger.
If the rains didn't come, it was handy
to be able to pull yourself...
...to the next swamp.
That was a very important adaptation.
The first amphibians evolved,
still with a fish-like tail.
Amphibians, like fish, laid their eggs
in water where they were easily eaten.
But then a splendid
new invention came along:
The hard-shelled egg, laid on land
where there were as yet no predators.
Reptiles and turtles
go back to those days.
Many of the reptiles hatched on land
never returned to the waters.
Some became the dinosaurs.
One line of dinosaurs developed
feathers, useful for short flights.
Today, the only living descendants
of the dinosaurs are the birds.
The great dinosaurs evolved
along another branch.
Some were the largest flesh-eaters
ever to walk the land.
But 65 million years ago they all
Meanwhile, the forerunners
of the dinosaurs...
...were also evolving
in a different direction.
Small, scurrying creatures...
...with the young growing
inside the mother's body.
After the extinction of the dinosaurs,
many different forms developed.
The young were very immature at birth.
In the marsupials,
the wombat, for example...
...and in the mammals, the young had
to be taught how to survive.
The brain grew larger still.
Something like a shrew was
the ancestor of all the mammals.
One line took to the trees,
...stereo vision, larger brains...
...and a curiosity
about their environment.
Some became baboons,
but that's not the line to us.
Apes and humans have
a recent common ancestor.
Bone for bone, muscle for muscle,
molecule for molecule.
There are almost no important
differences between apes and humans.
Unlike the chimpanzee,
our ancestors walked upright...
...freeing their hands
to poke and fix and experiment.
We got smarter. We began to talk.
Many collateral branches
of the human family...
...became extinct in
the last few million years.
We, with our brains and our hands,
are the survivors.
There's an unbroken thread that
stretches from those first cells to us.
Let's look at it again...
...compressing 4 billion years
of human evolution into 40 seconds.
Those are some of the things
that molecules do...
...given 4 billion years of evolution.
We sometimes represent evolution as
the ever-branching ramifications...
...of some original trunk...
...each branch pruned and clipped
by natural selection.
Every plant and animal
...has a history as ancient
and illustrious as ours.
Humans stand on one branch.
But now we affect
the future of every branch...
...of this 4-billion-year-old tree.
How lovely trees are.
The human species grew up
in and around them.
We have a natural affinity for trees.
...they harvest sunlight...
...they compete for the sun's favors.
Look at those two trees there...
...pushing and shoving for sunlight...
...but with grace
and astonishing slowness.
There are so many plants
on the Earth...
...that there's a danger
of thinking them trivial...
...of losing sight of the subtlety
and efficiency of their design.
They are great and beautiful
machines, powered by sunlight...
...taking in water from the ground
and carbon dioxide from the air...
...and converting them into food
for their use and ours.
This is a museum of living plants.
The Royal Botanic Gardens
at Kew in London.
Every plant uses
the carbohydrates it makes...
...as an energy source
to go about its planty business.
And we animals, who are ultimately
parasites on the plants...
...we steal the carbohydrates
so we can go about our business.
In eating the plants
and their fruits...
...we combine the carbohydrates
...which as a result of breathing,
we've dissolved in our blood.
From this chemical reaction, we
extract the energy which makes us go.
In the process,
we exhale carbon dioxide...
...which the plants then use
to make more carbohydrates.
What a marvelous
Plants and animals each using
the other's waste gases...
...the whole cycle powered
by abundant sunlight.
But there would be carbon dioxide in
the air even if there were no animals.
We need the plants
much more than they need us.
There are family resemblances
among the organisms of the Earth.
Some are very apparent,
such as the use of the number five.
Humans have five major
One head, two arms, two legs.
So do ducks...
...although the functions of their
projections are not quite the same.
An octopus or a centipede
has a different plan.
And a being from another planet
might be much stranger still.
These family resemblances continue
and on a much deeper level...
...when we go to the
molecular basis of life.
There are tens of billions...
...of different kinds
of organic molecules.
Yet only about 50 of them...
...are used in the essential
machinery of life.
The same 50 employed
over and over again...
...ingenious, for different functions
in every living thing.
And when we go to the very kernel
of life on Earth...
...to the proteins that
control cell chemistry...
...to the spiral or helix
of nucleic acids...
the hereditary information...
...we find these molecules
to be identical...
...in all plants and animals
of our planet.
This oak tree and me,
we're made of the same stuff.
If you go back, you'll find
that we have a common ancestor.
That's why our chemistry is so alike.
Let's take a trip to examine
this common basis of life.
A voyage to investigate
the molecular machinery...
...at the heart of life on Earth.
A journey to the nucleus of the cell.
First we need a cell.
I have trillions.
I can afford to donate a few.
The casual act of pricking a finger...
...is an event of some magnitude
on the scale of the very small.
Millions of red blood cells are
detoured from their usual routes.
But most continue
to cruise about the body...
...carrying their cargoes of oxygen
to the remotest freckle.
We're about to enter
the living cell...
...a realm, in its own way,
as complex and beautiful...
...as the realm of galaxies and stars.
Among the red blood cells,
we encounter a white blood cell...
...whose job it is to protect me
against invading microbes.
It makes antibodies
on its furrowed surface...
...but its interior is
like that of many cells.
Plunging through the membrane,
we find ourselves inside the cell.
Here, every structure
has its function.
These dark green blobs
...where messenger molecules
are busy building the enzymes...
the chemistry of the cell.
The messengers were
instructed and dispatched...
...from within the nucleus,
the heart and brain of the cell.
All the instructions on
how to get a cell to work...
...and how to make another
are hidden away in there.
We find a tunnel, a nuclear pore...
...an approach to
the biological holy of holies.
These necklaces, these intricately
looped and coiled strands...
...are nucleic acids, DNA.
Everything you need to know on
how to make a human being...
...is encoded in the language
of life in the DNA molecule.
This is the DNA double helix...
...a machine with about 100 billion
moving parts, called atoms.
There are as many atoms
in one molecule of DNA...
...as there are stars
in a typical galaxy.
The sequence of nucleotides,
here brightly colored...
...is all that's passed on
from generation to generation.
Change the order of the nucleotides...
...and you change
the genetic instructions.
DNA must replicate itself
with extreme fidelity.
The reproduction of a DNA molecule
begins by separating the two helices.
This is accomplished
by an unwinding enzyme.
Like some precision tool,
this enzyme, shown in blue...
...breaks the chemical bonds
that bind the two helices of DNA.
The enzyme works its way
down the molecule...
...unzipping DNA as it goes.
Each helix copies the other...
...supervised by special enzymes.
The organic soup inside the nucleus
contains many free nucleotides.
The enzyme recognizes an approaching
nucleotide and clicks it into place...
...reproducing another rung
in the double helix.
When the DNA is replicating
in one of your cells...
...a few dozen nucleotides
are added every second.
Thousands of these enzymes may be
working on a given DNA molecule.
When an arriving nucleotide
...the enzyme throws it away.
We call this proofreading.
On the rare occasions
of a proofreading error...
...the wrong nucleotide is attached...
...and a small random change has
been made in the genetic instructions.
A mutation has occurred.
This enzyme is a
pretty small molecule...
...but it catches nucleotides,
assembles them in the right order...
...it knows how to proofread...
in the most fundamental way...
...for the reproduction of every cell
and every being on Earth.
That enzyme and DNA itself...
...are molecular machines
with awesome powers.
Within every living thing,
the molecular machines are busy...
...making sure that nucleic acids
will continue to reproduce.
A minor cut in my skin
sounds a local alarm...
...and the blood spins
a complex net of strong fibers...
...to form a clot
and staunch the flow of blood.
There's a very delicate balance here:
Too much clotting
and your blood stream will solidify.
Too little clotting and you'll bleed
to death from the merest scratch.
The balance is controlled
by enzymes instructed by DNA.
Down here, there's also
a kind of sanitation squad...
...comprised of white blood cells,
that swings into action...
...surrounds invading bacteria
and ravenously consumes them.
This mopping-up operation is
a part of the healing process...
...again controlled by DNA.
These cells are parts of us,
but how alien they seem.
Within each of them,
within every cell...
...there are exquisitely
evolved molecular machines.
Nucleic acids, enzymes,
the cell architecture...
...every cell is a triumph
of natural selection.
And we're made of trillions of cells.
We are, each of us, a multitude.
Within us is a little universe.
Human DNA is a coiled ladder...
...a billion nucleotides long.
Many possible combinations of
nucleotides are nonsense. That is...
...they translate into proteins which
serve no useful function whatever.
Only a comparatively few
nucleic acid molecules...
...are any good for life forms
as complicated as we are.
But even so, the number of useful ways
of assembling nucleic acids...
...is stupefyingly large.
It's probably larger than the total
number of atoms in the universe.
This means that the number of
possible kinds of human beings...
...is vastly greater than the number
of human beings that has ever lived.
This untapped potential of
the human species is immense.
There are ways of
putting nucleic acids together...
...which will function far better
by any criterion you wish to choose...
...than the hereditary instructions of
any human being who has ever lived.
Fortunately, we do not know,
or at least do not yet know...
...how to assemble alternative
sequences of nucleotides...
...to make alternative kinds
of human beings.
In the future, we might be able
to put nucleotides together...
...in any desired sequence...
...to produce human characteristics
we think desirable.
A disquieting and awesome prospect.
We human beings don't look
very much like a tree.
We certainly view the world
differently than a tree does.
But down deep,
at the molecular heart of life...
identical to trees.
We both use nucleic acids
as the hereditary material.
We both use proteins as enzymes
to control the chemistry of the cell.
And most significantly,
we both use the identical code book...
...to translate nucleic acid information
into protein information.
Any tree could read my genetic code.
How did such astonishing similarities
Why are we cousins to the trees?
Would life on some other planet
The same proteins? The same nucleic
acids? The same genetic code?
The usual explanation
is that we are...
...all of us, trees and people...
...anglerfish, slime molds,
...all descended from a single
and common instance...
...of the origin of life
4 billion years ago...
...in the early days of our planet.
...did the molecules
of life arise?
In a laboratory
at Cornell University...
...we mix together the gases
and waters of the primitive Earth...
...supply some energy...
...and see if we can make
the stuff of life.
But what was the early atmosphere
made of, ordinary air?
If we start with
our present atmosphere...
...the experiment is a dismal failure.
Instead of making proteins
and nucleic acids...
...all we make is smog,
a backwards step.
Why doesn't such an experiment work?
Because the air of today
contains molecular oxygen.
But oxygen is made by plants.
It's obvious that there were
no plants before the origin of life.
We mustn't use oxygen
in our experiments...
...because there wasn't any
in the early atmosphere.
This is reasonable because the cosmos
is made mostly of hydrogen...
...which gobbles oxygen up.
The Earth's low gravity has
allowed most of our hydrogen gas...
...to trickle away to space.
There's almost none left.
But 4 billion years ago...
...our atmosphere was full
of hydrogen-rich gases:
Methane, ammonia, water vapor.
These are the gases we should use.
Taking great care to ensure
the purity of these gases...
...my colleague, Bishun Khare,
pumps them from their holding flasks.
An experiment like this
was first performed...
...by Stanley Miller
and Harold Urey in the 1950s.
The starting gases are now introduced
into a large reaction vessel.
We could shine ultraviolet light,
simulating the early sun.
But in this experiment...
...the gases will be sparked...
...as the primitive atmosphere was
by early lightning.
After only a few hours,
the interior of the reaction vessel...
...becomes streaked with
a strange brown pigment...
...a rich collection
of complex organic molecules...
...including the building blocks of
the proteins and the nucleic acids.
Under the right conditions, these
building blocks assemble themselves...
...into molecules resembling little
proteins and little nucleic acids.
These nucleic acids can even make
identical copies of themselves.
In this vessel are the notes
of the music of life...
...although not yet the music itself.
Now, no one, so far...
...has mixed together the gases
and waters of the primitive Earth...
...and at the end of the experiment
had something crawl out of the flask.
There's still much to be understood
about the origin of life...
...including the origin
of the genetic code.
But we've only been at
such experiments for 30 years.
a 4-billion-year head start.
Incidentally, there's nothing in such
experiments that's unique to the Earth.
The gases we start with,
the energy sources we use...
...are entirely common
through the cosmos.
So chemical reactions something like
these must be responsible for...
...the organic matter
in interstellar space...
...and the amino acids
in the meteorites.
Similar chemical reactions
must have occurred...
...on a billion other worlds
in the Milky Way galaxy.
Look how easy it is to make
great globs of this stuff.
The molecules of life fill the cosmos.
What would life elsewhere look like?
Even if it had an identical molecular
chemistry to life on Earth...
...which I very much doubt...
...it could not be
very similar in form...
...to familiar organisms on the Earth.
The random character of
the evolutionary process...
...must create elsewhere creatures
very different from any that we know.
Think of a world
something like Jupiter...
...with an atmosphere rich in hydrogen,
helium, methane, water and ammonia...
...in which organic molecules
...falling from the skies
like manna from heaven...
...like the products of
the Miller-Urey experiment.
Could there be life on such a world?
There's a special problem.
The atmosphere is turbulent...
...and down deep, before we ever
come to a surface, it's very hot.
If you're not careful,
you'll be carried down and fried.
If you reproduce
before you're fried...
...turbulence will carry your offspring
into the higher and cooler layers.
Such organisms could be very little.
We call them sinkers.
The physicist E.E. Salpeter and I
something about the life...
...that might exist on such a world.
Vast living balloons could
...by pumping heavy gases
from their interiors...
...or by keeping their insides warm.
They might eat the organic molecules
in the air...
...or make their own with sunlight.
We call these creatures floaters.
We imagine floaters
...enormously larger than
the greatest whale that ever was...
...beings the size of cities.
We conceive of them arrayed
in great, lazy herds...
...as far as the eye can see...
...concentrated in the updrafts
in the enormous sea of clouds.
But there can be other creatures
in this alien environment: hunters.
Hunters are fast and maneuverable.
They eat the floaters,
both for their organic molecules...
...and for their store
of pure hydrogen.
But there can't be many hunters...
...because if they destroy all the
floaters, they themselves will perish.
Physics and chemistry permit
such life forms.
Art presents them with
a certain reality...
...but nature is not obliged
to follow our speculations.
If there are billions of inhabited
worlds in the Milky Way galaxy...
...then I think it's likely there are
a few places which might have...
...and floaters and sinkers.
Biology is more like history
than it is like physics.
You have to know the past
to understand the present.
There is no predictive theory of
biology, nor is there for history.
The reason is the same:
Both subjects are still
too complicated for us.
But we can understand ourselves
...by understanding other cases.
The study of a single instance
of extraterrestrial life...
No matter how humble,
a microbe would be just fine.
...will de-provincialize biology.
It will show us what else is possible.
We've heard so far the voice
of life on only a single world...
...but for the first time,
as we shall see...
a serious scientific search...
...for the cosmic fugue.
Recently, we've learned more
about the origin of life.
Do you remember RNA...
...that nucleic acid
that our cells use as messengers...
...carrying the genetic information
out of the cell nucleus?
Well, it's been found that RNA,
...can control chemical reactions...
...as well as reproduce itself,
which proteins can't do.
Many scientists now wonder
if the first life on Earth...
...was an RNA molecule.
It now seems feasible that
key molecular building blocks...
...for the origin of life, fell out
of the skies 4 billion years ago.
Comets have been found to have a lot
of organic molecules in them...
...and they fell in huge numbers
on the primitive Earth.
We also mention the extinction
of the dinosaurs...
...and most of the other species on
Earth about 65 million years ago.
We now know that a large comet
hit the Earth at just that time.
The dust pall from that collision
must've cooled and darkened the Earth...
...perhaps killing all
the dinosaurs, but sparing...
...the small, furry mammals
who were our ancestors.
Other cometary mass extinctions
in other epochs seem likely.
If true, this would mean that
comets have been the bringers...
...both of life and death.