Learn about the origin and evolution of life and the search for life beyond the Earth.
History of Astrobiology
Loading...
Do curso por The University of Edinburgh
A Astrobiologia e a Busca por Vida Extraterrestre
1132 classificações
Na lição
Life and Its Origins
What is life and what are the definitions of life? What do we know about the origin of life and what are the current hypotheses for how it originated on the Earth?
Conheça os instrutores
Charles CockellProfessor
Astrobiology
[BLANK_AUDIO]
We've learned what astrobiology is.
It's always very useful in Science, if you
want to get some perspective, to understand the history.
Because the history of a subject can tell you how you've got to the place you're at
at the moment and what it was that led to the state of knowledge that we have today.
So let's look at the history of Astrobiology and get
an overview of some of the early thoughts in this field.
And how it is that we have come to the state of knowledge that
we understand about the possibilities of life beyond Earth today, and
our understandings of the history and evolution of life on Earth.
You'll often here people say that astrobiology
is a very new science, an emerging science.
It's certainly true to say that astrobiology has
developed very rapidly in recent years, and the experimental
methods that are now being developed, new missions and
new telescopes, are making this a subject that's advancing
at a remarkable rate. But it's certainly not a new science.
People have been contemplating the possibility
of habitable worlds, for a long time.
This is a really rather remarkable
statement by Metrodorus, an ancient Greek philosopher.
Who was actually a student of Democritus,
who first proposed the atomic theory of matter.
And this is in loose translation of what he said.
He said, it would be strange if a single
ear of corn grew in a large plain,
although only one habitable world in the infinite.
Metrodorus was expressing the idea that if you
go into a field it's very unusual to see
one ear of corn growing in the middle of a field with no other corn around it.
Generally if you go into a field and you see corn you'll see a lot of it.
And he wondered if there is life on this planet, then surely there
must be other worlds with life as well.
Well, the ancient Greeks didn't quite have the
same perception as the heavens that we do.
They don't under, they didn't understand about planets, and
they didn't understand the nature was of other stars.
But nevertheless this was a remarkable statement for people thinking in early
years astrobiology over 2,000 years ago about the possibility of inhabited worlds.
As we go on through history we find other speculations that are just as remarkable.
In the 16th century during the Renaissance this was a statement made by
Giordano Bruno, who was an astronomer speculating
about the possibility of planets beyond Earth.
And it's worth reading what he said.
He said in space there are countless constellations, suns, and planets, we only
see the suns because they give light.
The planets remain invisible for they are small and dark.
There are also numberless Earth's circling around their suns.
Now if you think about this statement today, in an age where we are beginning to
detect Earth-like planets around other stars, this is
a truly remarkable speculation for the 16th century.
I'm not a great fan of calling people fathers or mothers
of particular fields of science, I don't think
it does good things for the human ego.
But if you really want a father of
astrobiology, you would probably give it to Giordano
Bruno, person who speculated on the presence of
other Earths orbiting other stars in the 16th century.
Bruno unfortunately was burned at the stake in 1600, not just for
his astrobiological speculations, he did other things that incurred the wrath of
his religious superiors.
But he was the first astrobiologist at least to meet
his fate speculating amongst other things about life beyond Earth.
The invention of the telescope allowed us to
go beyond these speculations, to see planets around other
stars, and to start to form more empirical
ideas about whether other planetary bodies could sustain life.
And you might think that
once the telescope had been invented there
would be a lot less speculation, because now
we'd have real data about other planetary bodies
on which we could base ideas and speculations.
But in fact, remarkably, completely the opposite happens now
we have telescopes, we can see other planetary bodies.
But we don't have enough information to know what their environments are like.
So now we've got all these new planets on which we can speculate about the presence
of other life.
And the invention of the telescope of Galileo, and you
can see here one of the first images that he
looked at, which was the moons Jupiter, the four largest
moons of Jupiter, now called the Galilean moons of Jupiter.
This invention of the telescope and its widespread use led to the discovery of
planets that caused speculation to run riot during the Enlightenment.
This is
a speculation by the famous scientist William Hershel, who wrote, whilst
observing the moon, by reflecting a level on the subject I'm almost
convinced that those numberless small Circuses we see on the moon
are the works of the Lunarians and may be called their Towns.
Herschel was observing asteroid craters on the
moon, craters that seemed almost perfectly circular.
So circular, they couldn't have possibly have been formed
by natural processes.
The must be the work of an intelligence, and he believed that the
moon might be inhabited by Lunarians, who
were constructing these fortifications on the moon.
And even Christian Huygens, famous astronomer,
observed spots on Venus, Mars, and Jupiter.
Spots that we now know are features of
storms and, and deserts on the surface of Mars.
And he concluded there were clouds and
water and he stated, the taste of music with the inhabitants of Venus
and Jupiter is at a high level, similar to that Frenchmen or Italians.
Now these observations today seem crazy to us and they seem crazy particularly
because they came from extremely erudite scientists
that achieved remarkable things in their field.
But it shows how with a very limited set of
data people began speculating about life on other planets and I
should say that these speculations are also a warning from the past.
A warning about being too optimistic in
astrobiology and we should be careful today
in learning the lessons from our forebears
about over speculation with very little data.
Even in the 20th century, speculation runs riot.
Percival Lowell the Astronomer who observed lines
across the surface of Mars, an optical processing
trick of the human brain which he interpreted
to be canals, built by a dessicated dying
civilization on Mars, trying to channel water from
the polar icecaps to the equatorial regions of Mars.
And he observed these canals over and over again.
So convinced was he, he wrote this Every opposition is added to the assurance that
canals are artificial, both by disclosing their peculiarities better and better and
by removing generic doubts as to the planet's habitability.
The first person to really connect habitability with
intelligence on a planet in our own solar system.
We now know, of course, there are no canals on Mars.
Percival Lowell was deluded by his observations.
But it shows that even in the 20th century people thought
there might be intelligences on other planets in our solar system.
Aliens still
grip the human imagination.
You only have to watch films produced by
Hollywood and other production companies around the world.
Aliens are pervasive throughout popular culture, from Star
Wars to The Extraterrestrial, to the War of the
Worlds, and on and on it goes, a long list of aliens that we've seen in films.
So you can see how, optimism about astrobiology in
particular intelligent life still grips the human imagination and
we have to be very careful to separate
what our imagination wants us to believe and
what the data, what the knowledge that we
have from telescope and missions, is really telling us.
That is a very important lesson in astrobiology and indeed in any science.
In the 1950's and early 1960's, the space age began to
unfold, and with it, the possibility of sending spacecraft to other planets.
And we started to get views from spacecraft orbiting Mars and Venus.
And these views were rather depressing.
On the left hand side there you can see an image from Mariner 4 from 1965.
And Mars looks like
a dead desert, there's no obvious canals there, no intelligent civilizations.
And on the right, you can see an image taken by
the Soviet Venera spacecraft, that landed on the surface of Venus.
And again no Venetians playing music like
Frenchmen or Italians, just a dead planetary surface.
And these visions of our solar system really
caused I would say almost a sense of depression
even among scientists during that period about
the possibility of life throughout our solar system.
No evidence of civilizations, not even any evidence for
simple life forms, even microbial life on these planets.
And so the early years of the space age, were a period
where people began to backtrack in their optimism about life beyond Earth.
But ironically, as these spacecraft improved, and
as our cameras improved, we began to see details.
Details that suggested that we might not be quite as negative, as we
thought we needed to be in the early years of the space age.
People began to see valley networks on the surface
of mars, outflow channels that suggests liquid water on the
early surface of that planet and now, we know
quite conclusively, that there was much more abundant liquid water
on the surface on Mars early in its history.
And as we saw earlier in this course, liquid
water is necessary for life as we know it.
So the presence of liquid water on the early history of Mars, in the early
history of Mars suggests that this is a
planet that may have been habitable for life.
This is a remarkable image of Jezero crater on mars, and
you can see an ancient Martian river flowing out into a crater.
And these deposits, that are essentially
deposits of sediments in a delta.
This is an ancient lake on the surface of Mars.
Could it have harbored life?
Well, this is one of the questions that we're looking at.
But as the space age developed, so astrobiology has moved into perhaps
a more optimistic stage of considering the possibility of life beyond Earth.
What were the other developments that allowed astrobiology
to make the transition from a philosophical and
speculative science in ancient Greece and in the Renaissance.
To an empirical science constrained by data.
Well, let's have a look at some of these early developments.
And, possibly one of the most important experiments was
one conducted in 1952, when the scientists Urey and Miller,
who were interested in the origin of life, and they
carried out an experiment, to simulate an early Earth atmosphere.
And you can see this
rather ingenious apparatus where they've got some water boiling away inside a
flask, being circulated into another container
that's got an electrical discharge apparatus.
And this electrical discharge is discharging
across an ancient simulated Earth atmosphere.
And they circulated this water round and round.
And after a period of time, they found
that the gases in this container, once they
had been electrically sparked, transform themselves into amino acids,
that we saw, are the building blocks of life.
So, in this simple experiment, using only water and the constituents of
early Earth atmosphere, these scientists managed
to create the building blocks of life.
This was a truly remarkable experiment, a breakthrough in astrobiology that
allowed scientists to go from speculation about the origin of life,
to thinking about how those early building blocks might well have formed.
Nowadays we think that the atmosphere of early Earth is actually slightly different
from the atmosphere that was used by Urey and Miller in the early experiments.
But nevertheless this remains a remarkable and landmark experiment in
the early history of Astrobiology, at least in the twentieth century.
And taking our understanding of the origin of life to a new, empirical level.
Alongside these sorts of studies people were beginning to study the early rock
record on the Earth, to try and find evidence for early life on Earth.
Collecting rocks, breaking them open, and trying to see whether there was life.
These are some images of ancient microfossils from the Apex Chert, which is
a type of ancient rock found in Australia. Well over, 3 and a half billion years old.
And these are, purportedly, the microfossils, fossils
of the earliest life forms on Earth.
Well, these fossils are highly
controversial, and many scientists argue about,
the nature of different types of fossils in the rock record.
Are they biological?
Are they produced by chemical processes?
And we'll look in a bit more detail at that in a future lecture.
For these early studies of fossils in the rock, record were pivotal in
beginning to take, again our understanding of the early
evolution of life on Earth to a new scientific level
where we can start to argue about evidence for fossils
in the rock record, an argument that continues vigorously today.
And other experiments were also taking
astrobiology into new territory, scientific territory.
We looked at some of the early evidence for, the lack of civilizations on Mars.
Well, by the 1970s, we were able to send spacecraft to the surface of Mars.
And the Viking I and II landings which are shown here, carried out
the first biological experiments on the surface of Mars, to search for life.
Their results
were inconclusive and again these are highly controversial
results that many scientists continue to argue about today.
Did Viking I and II find life or did they not?
Well these, experiments will be backed up or not supported, as the case may be, by
the Mars Science Laboratory and other rovers and
missions that will travel to Mars in the future.
For the Viking I and II missions to Mars in the mid 1970s.
Again,
were a breakthrough in Astrobiology because
they were the first real experiments, the
first empirical experiments to search for life on the surface of another world.
And they took Astrobiology from
early speculations to new experimental discoveries.
Other very interesting experiments occurring even in the 1970s.
The first, signal was sent out to
alien intelligences from the Arecibo Dish Observatory
in Puerto Rico.
And you can see the image of the message that was sent out into space here.
It was sent out in binary code, and it included lots
of information, such as, for example, a diagram of DNA, the information
storage system of life, a diagram of a human being, A
map of our solar system and even the numbers one to ten.
Well, this message was very short, and it probably
will not be picked up by an alien intelligence,
but nevertheless, the first experimental
attempt to communicate with alien intelligences.
A new and remarkable experiment in the
search for and communication with extraterrestrial intelligence.
In very recent times we've seen new experiments to study the environments
of other planets and see whether they might be capable of supporting life.
These images sent back by the Mars science laboratory of
ancient rivers and ancient river beds on
Mars conglomerated rocks that have believed to have
formed By flowing water at the bottom of rivers on Mars, over 3 billion years ago.
Evidence that there was liquid water on Mars, and
evidence that these are the sorts of places where
we might try and search for evidence of life,
or at least see whether these environments were habitable.
And beyond Mars in the last
two decades other extraordinary discoveries that are taking astrobiology
into new realms and new locations to search for life.
This incredible image of Enceladus a tiny moon of the planet Saturn.
And there's evidence that there are geysers erupting from the south pole of
this moon, throwing out water and
other elements into space including organic carbon.
The Cassini spacecraft that flew through these plumes, discovered different
elements like, silicate, sodium, water, also methane and complex organic carbon.
Is Enceladus a location for life?
Well at the moment we don't know, but this is certainly
a very promising target for Astrobiologist to explore in the future.
And might be one of the best places to study early chemical
reactions, that might've been responsible for the origin
of life, or even to search for life itself.
Other moons have been discovered that are covered in interesting chemistry.
This is the moon Titan, another moon of Saturn.
The Huygens probe landed on the surface of
Titan a few years ago and took these images.
Showing surface of Titan covered in these rocks.
These rocks are actually made of ice,
icy water.
But they're in an environment that's very different from
one that you and I may be familiar with.
Here, the rivers are made of liquid
methane and other types of hydrocarbons like ethane.
This an alien world, but an alien world full
of organic chemistry, which might tell us something about the
early evolution of life on the Earth and how
organic chemistry gives rise to the building blocks for life.
This is a promising location for
astrobiologists to understand the chemistry
that's necessary for early pre-biology.
And I think it's true to say, and this is not
an exaggeration, but the most
extraordinary development in astrobiology over the
last two decades, has been the search for planets around other
stars, and particularly recent searches for Earth like planets around other stars.
This is one of the holy grails, if you like,
of astrobiology to find a second Earth orbiting another star.
In recent years most of the planets that have
been discovered are too hot, they're too close to their
star or they're too large, they're gas giant planets
that don't have rocky surfaces, necessary, we think, for life.
But in the last couple of years, planets
are being discovered around other stars, the size
of the Earth or slightly larger than the
Earth, that may have conditions suitable for life.
The search for Earth-like planets around other stars is surely
one of the most incredible developments in astrobiology in recent years.
And one of the most extraordinary vindications of that early speculations
by Giordano Bruno about the possibility of numberless Earths orbiting other stars.
So what have we learned in this lecture?
We've learned that despite everything we hear about astrobiology
being a new science, it's actually an ancient science.
That began in the philosophical schools of ancient Greece.
It's only recently it's become very
scientifically constrained with new missions and
spacecraft that have allowed us to study the surfaces of other planets
and new studies of ancient rocks that have allowed us to study
the possibilities of early life on Earth and how life first originated on
our planet.
We have also learned there are several
planetary bodies in our solar system that have
become of interest in the search for life and we'll be explored in future years.
We can now hunt for Earth-like planets around other stars in
our galaxy, opening up vast realms of space to astrobiologists to
search for life, and study whether the experiment in biological evolution
that has occurred on the Earth, may have occurred somewhere else.
I think we can say without
a shadow of doubt, the future will hold many remarkable
discoveries and surprises in this rapidly developing field of astrobiology.
[BLANK_AUDIO].
Explore nosso catálogo
Registre-se gratuitamente e obtenha recomendações, atualizações e ofertas personalizadas.
O Coursera proporciona acesso universal à melhor educação do mundo fazendo parcerias com as melhores universidades e organizações para oferecer cursos on-line.
© 2018 Coursera Inc. Todos os direitos reservados.
