Hi I'm Sarah Walker and I'm professor at
Arizona State University and I am an
astrobiologist. That studies the origin
of life. And so one of the questions you
might have as an astrobiologist is
why is origin of life so critical to the
study of astrobiology.
Well, astrobiologists are really interested
in whether or not we can identify a
living world so if we can identify
life on another planet.
We wanna discover aliens and
ultimately, the question is whether we'll
be able to distinguish planets that have
life from plants that don't have life. So
in our own solar system, we can actually
send robotic missions to other planets
to look for life on the surface of those
worlds but we're thinking about
exoplanets and planets and distant solar
systems all that we're gonna get is a
little bit of data about the entire planet.
And so, as astrobiologists we are
interested in thinking about life not
only at the scale of individual
organisms, but also at the scale of
entire planets.
And so just to talk about the
magnitude of the problem a lot of people
want to talk about looking at life in
kind of new ways and maybe trying to use
insights from different aspects of known
fields of science to try to understand
how we identify life. And so, on this
slide I'm showing two worlds that are
probably familiar to everyone. Jupiter
and Earth and we know one of these
planets is inhabited and the other isn't.
The inhabited world is obviously our
very own earth, and we can see living
structures on its surface what we see
here is cities at night. When we're
thinking about how to think about the
problem of distinguishing the living
process on Earth from the nonliving
process on Jupiter, it's clear that both
have non-equilibrium structures on
their surfaces. So Jupiter for example
has this great red spot and as I
mentioned, earth has cities. So when we
want to talk about defining the
properties of those planets that are
associated with life, it's not just about
this disequilibra. Clearly cities are
fundamentally different than the great
red spot of Jupiter even though they're
both non-equilibrium structures. So we
have to move a little bit further and
understand the origins of the processes
that led to structure
on the surface of our planet that are
associated with life, and the root of
that question is really to understand
what's the probability of life emerging
on a planet and how can we actually
understand that as a planetary scale
process. And there's really two ways of
constraining the likelihood of life
emerging on a planet. We don't
think that Jupiter is a living planet. Obviously
based on our observations of Jupiter, it
could be that it might satisfy some
definition of life down the road if we
actually come up with a theory for life
and Jupiter satisfies that theory but
right now we don't think Jupiter's alive.
And so we need some observations of
other living world to constrain the
probability of life right now earth is
the only example we know and so to do
that we actually have to detect alien
life and determine its abundance. And so
this is the way you usually people think
about astrobiology is actually looking
at other worlds trying to identify if
there's aliens on those worlds and then
maybe we would actually be able to
constrain the probability that a planet
like Earth is going to emerge life on
its surface and a planet like Jupiter is
not. But we can also think about theory
and experiment to constrain the
probability for life. And from this view
the idea is really to try to uncover
what are the universal principles of
life that might actually allow us to
build predictive models for the
circumstances under which life should
emerge. So, we would have some a priori
theory that would enable us to predict P(life)?
the probability of life emerging.
And so with the Jupiter and Earth
example I gave that theory should be
able to account for the differences that
it's not just a non-equilibrium process
on the surface of a planet but in the
case of formation of cities or forests
or any of the kind of rich structure
that we see on earth that's a product of
biology that the theory would be able to
explain what those things are and be
able to predict what kinds of other
examples of life we might be able to see
on other planets and their likelihood.
But really what we're talking about in
order to constrain the probability of
life is not just to think about the
probability of forests or cities on the
surface of planets as opposed to the
probability of great red spots or other
kinds of dissipative structures that
aren't alive. What we really want is to
understand what's the likelihood of life
even emerging on that planet.
So we really need to be able to solve
the origin of life problem in order to do
astrobiology effectively and constrain
the likelihood of life in the universe.
And so in order to do that, we have to
come up with better theories for origins
of life and be able to understand how
life emerges. And so one of the ways I
like to think about it is really that
we're looking for new principles that
would explain life not just on earth but
life on other planets and I really love
this quote from David Deutsch which I
think articulates very nicely the kind
of processes that are happening on
planets that we really need to be able
to understand in order to understand
life. And he says, base metals can be
transmuted into gold by stars and by
intelligent beings who understand the
processes that power stars and by
nothing else in the universe. So we have
a physics that explains things like
stars or the physics of Jupiter and why
Jupiter has a great storm
on the surface of the planet at the
great red spot. But we don't have a
physics that explains the evolution of a
planet like our own. How life emerges on
that planet, or how it evolves over time
to lead to the kind of diversity of
structures that we have on the surface
of our planet today, like cities and
thinking human beings. Origin
'life problem is really a problem of how
that entire process of life gets started
in the first place and it's ultimately
critically important to the field of
astrobiology that we understand that
process because we want to know on how
many worlds that occurs.