An introduction to modern astronomy's most important questions. The four sections of the course are Planets and Life in The Universe; The Life of Stars; Galaxies and Their Environments; The History of The Universe.
Appearance of Life
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From the course by University of Rochester
Confronting The Big Questions: Highlights of Modern Astronomy
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From the lesson
Are we alone in the Universe?
Planets and Life in The Universe - Exoplanets searches, exoplanet census, astrobiology
Meet the Instructors
Adam FrankProfessor
Physics and Astronomy
Okay. Welcome back everybody.
Now we have what we need to understand the origins of life,
or at least to understand our understanding of the origin of life.
So we want to talk about the appearance of life
in the universe and what should be involved in that.
so, you know we talked about the Drake Equation and the last
three terms in the Drake Equation are all about the creation of life.
Which planets actually form life.
Which kinds of life forms intelligence.
Which kinds of intelligence forms technological
civilizations and how long do those civilizations last.
Now we really can only guess about those terms, but
you know, for the first one, when does life form?
We do actually have some information by, based on our
understanding of chemistry and some experiments that we've actually done.
So now of course, you know, what is life is
kind of an open question and you can certainly ask.
You know, is it possible to have the kinds of life that
maybe we wouldn't recognize as being alive, you know viruses are right on
the boundary between what, you know, might be
defined as being alive or not being alive.
But, you know, we're going to put that aside for right now, we're
just going to try and focus on life that, you know, is clearly recognizable.
So for example, what, what are criterion for defining something made of life.
Well if we're going to talk about, you know, the life
that we recognize, it's something that's composed of organic molecules.
You know, chains or rings of carbon or
some other you know very chemically active element.
We certainly expect there to be metabolism, right?
The ability to consume energy.
And of course if you're consuming energy, thermodynamics tells
us you're gotta have to produce waste as well.
So we expect that metabolism is going to be part of a definition of life.
Reproduction, we expect that there should be more, you know, that as time
goes on, you're going to produce more of whatever you started with, right?
That reproduction the replication uh,maybe not exact of you
know the existing beings or existing examples of, of life should be part of it.
Mutation is very important, because if you don't
have mutation, you don't have the possibility of evolution.
So we expect that mutation in some
form should play an important role via evolution.
We expect evolution to be, we believe
evolution should be a fairly universal processes.
And then a sensitivity to the environment, that also ties into evolution.
because you know, if the environment changes, you expect that
you have to respond to it or you die, right.
And one of the things about mutations is that mutations will
create the possibility for organisms to respond positively to their environment.
If you know, the environment gets drier and
you have a random mutation that allows you to
use water better that, you're going to tend to
have your offspring making it to the next generations.
Okay, so here's
the basic criteria.
What do we, what can we do to think about how life actually formed?
Well, one amazing experiment that was done back
in the 1950's, and it's been replicated many times
came from the idea of some scientist asking
what were the conditions on the early earth like.
And would it be possible that those conditions
could lead to the building blocks of our life.
So this is something that was called the Miller-Urey Experiment.
And basically what they did is in a test tube, or
series of test tubes, they built a model of the early Earth.
And so there was water that was being heated by geological processes.
And there was material in the water that you would expect to
find, all the elements that you'd expect to find in the early Earth.
They also had an electric discharge tube.
And there that would create lightning.
And so you know, they basically, you know, put all this stuff in, the water,
the elements, the lightning, turned it on and you know, went away for a while.
They came back in a week or so, and what they
found was this goo at the bottom of their test tube.
And when they looked at it, they were, you know, amazed to find that basically many
of the building blocks, the amino acids that
are needed to form proteins, were already there.
And this really gave the indication that
you don't need much to sort of get the process started.
Now, of course, it's a long way from amino acids to a self-replicating molecule,
but of course, that long way is taken care of, in some sense, by time.
The the stretches of time over which evolution occurs are,
you know, tens of millions, hundreds of millions, billions of years.
And so if you have this goo at the bottom of, you know, of a pool of tide water.
And these
molecules are colliding with each other,
by just, you know, random collisions, eventually
you're going to sample, you're going to
start testing all the different possible configurations.
And some of those configurations may
eventually lead to a self-replicating molecule.
And the interesting thing about that is what you then get is chemical evolution.
Once you have a self replicating molecule, then basically what it does, it eats
up all the other elements or other chemicals in the in the pool and
it dominates.
So you know, once you can start getting self replication
really remarkable things can take into can begin to occur.
Now, there are, you know, difficulties with this scenario.
There's things we clearly don't understand.
And one of the things that people, that seems to
be clear, is that trying to get, go straight to
DNA from, you know, a bunch of amino acids at
the bottom of the tide pool may be very difficult.
And so people have begun to think about the possibilities of getting a first there
being an RNA world, that the world was full of
RNA that then was an intermediary step for forming DNA.
and part of that intermediary steps may
be developing molecules that acted as Autocatalysts.
Now catalyst is something that helps a
chemical of a reaction along, speeds it up.
And so if you actually had a replicating molecule that could act
as its own catalyst.
Then you could really, you know, drive the
process much faster and produce, self replicating molecules,
that were more robust, and that had a
greater opportunity to, exist in your, your tide pool.
But also tide pools may not be the only place that this could have occurred.
Some people have said ice actually is, as remarkable as it may be.
Would be a great place to get the building
blocks of life assembled, because there is water of course.
You know in little crevices.
and also there was the ice would act as a matrix that
would, you know, something that would hold the elements these elements together.
Allowing them to interact more closely.
So there's still you know, very many open questions.
But the the fundamental pieces we need
for understanding how you get a biogenesis, the
idea of taking nonlife and turning it into
life, those pieces are, are actually pretty solid.
It really becomes sort of the
mathematics of, or the statistics of, how long it takes for these interactions to
occur before you can sample all the
possible molecules and end up with a replicator.
So that's really something that is quite
remarkable that in our understanding of life.
So you know what we can see now is that we know we've come to
the point where we have a pretty firm
understanding of how life on the earth works.
And through that, we've been
able to develop at least a theoretical account
for how life would begin on other planets.
And one of the fascinating things we're going to be
looking for as we explore other planets, at least through
telescopes, over the next 20, 30 40 years, is
seeing whether we can actually get examples of other biologies.
To the other biologies will we see any evidence for other biologies by looking
at the atmospheres of other planets, or perhaps even within our own solar system.
We have places like Mars which you know, certainly looked like
they could have been habitable for their early parts of their existence.
And maybe underground in Mars there are places where it still is habitable.
At least for bacteria.
We also have things like Europa which is one of
the moons of Jupiter which is really an ocean essentially.
It's an ocean covered by ice with a rocky core.
And if there's geological activity which is creating at that with
that has thermal vents.
Those thermal vents are energy source which perhaps
life may have gotten the toe hold there.
So there may even be places on, in our
own solar system where at least bacterial life has emerged.
Now one thing to understand about this story.
About, about our understanding of life is that the earth's record of
life, gives us some really interesting clues to what may have happened.
For example, the earth was formed about
4.5 billion years ago.
And we have fairly good evidence that life appeared
pretty quickly after the emergence, or after the planet cooled.
So you know, within by, by 3.8 billion years ago or 3.4 billion years
ago, we really have evidence that, that you know, there life had already started.
So what is that tells us?
Just that one fact you know sort of implies
that it wasn't hard to get least microbial life.
That, that bacteria maybe relatively easy to build.
You didn't
have to wait 70% of the age, the current age, of the planet for life to begin.
It seemed to have appeared pretty much right after the planet appeared.
So that right there is a piece of information that may indicate that the,
that term in the Drake equation about the fraction of planets that have life.
That may be, at least if we're talking about microbial life, may be quite high.
So that's something to remember as we go on to think about,
you know, the ultimate question is, are there other intelligent
species out there that maybe someday we might be able to talk to.
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