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.