Welcome. My name is Tom Nolan. I'm the Associate Dean in the School of Science and Engineering, and I'm here to welcome you to our second Harrington STEM lecture this year. I'm going to have Amy Bartholomew do our introduction of our speaker, but I just want to point out that we have one other. Let me push the buttons here. Nothing's happening. Our next talk is on November 15th. Pollen Analysis as a tool for forensic analysis of trace evidence. I think it's going to be another extremely nice topic that's appropriate for everybody. If you're not coming to all of our talks, don't miss the next two. Then we'll have information available on our website about the spring seminars. There's three of those. I'm not going to go through all of that right now. Right now, I'm going to introduce Amy Bartholomew from the Astronomy and Physics department. [APPLAUSE]. We need a little of adjustments here. Do you need anything else? No. That's it here. No. You don't. Awesome. Hi, everybody. Thank you for coming. I'm just going to to introduce our speaker today. Caleb Scharf. He is the Director of the Columbia Institute. Sorry. Columbia Astrobiology Center. He received his bachelor's degree from Durham University in physics and then went on to get his PhD in astronomy from the University of Cambridge. His original background is in x-ray, astronomy and observational cosmology, but he has more recently turned to studying life in the universe, extrasolar planets and astrobiology. He has quite an extensive record of peer-reviewed literature and articles and he also has written a textbook for undergraduate astrobiology courses. He additionally has written two popular fiction books that you might like to look at called Gravity's Engines: The Other Side of Black Holes. [inaudible 00:02:10]. [LAUGHTER]. Yes. Thank you. Yeah. Fiction books, nonfiction [LAUGHTER] and like a friend of his, [inaudible 00:02:16] sorry, yes, they're popular nonfiction books [LAUGHTER] and in addition to that, he does a lot of popular publications and he does write a blog and it's published on the Scientific American website. You can follow him there for more information. Without further ado, we are very pleased to welcome Caleb Scharf. Thank you very much. I had to correct you on the fiction, nonfiction. [LAUGHTER] I mean, it'd be lovely to be a fiction writer, but thank you. Well, it's a great pleasure to be here this afternoon. Thank you very much for having me. Today, I'm going to spend some time taking you through a bit of an overview of this field we call astrobiology, which I termed the science of life in the universe. I'll also plunge into a few details on some of the work that I'm involved in and some of the ideas that I think are bubbling up for the near future. Astrobiology is an interesting field, and it's interesting because the questions beneath it, the questions driving it, the questions that are deep questions for our species and having deep questions for a long time, even in a non-scientific context. All of astrobiology, I think can be summed up, Let's see if my remote works. Yes. No, there's a delay, in these two questions, "Are we alone and where do we come from?" Simple questions, but they are the root of astrobiology. To start with, I'll spend a little bit of time on the, "Are we alone?" question, and later on I'll drift somewhat into the "Where do we come from?" question. Again, these are questions that now can be tackled with the rigor of science. They're also questions that I think even at an emotional level, matter to our species. Let me plunge right in and try to deal with question number one with a little bit of rigor. To do that, I'm going to talk for a moment about this idea of Bayesian Analysis. This question, [LAUGHTER] all right, I'm not going to use that. I'm just going to because it will keep revealing all my secrets. [LAUGHTER] [NOISE] This question of so, okay, life has happened here. What does that tell us about the odds of life happening elsewhere? If you stop someone on the street and ask them, do you think we're the only life in the universe? I wouldn't necessarily recommend it, especially in Manhattan, you might get some very strange looks. But if you do that very often the answer is, for people thinking about it is, well, look it's a huge universe and we're here, so yeah, sure, there's got be something else out there. The chances of us being the only example of life, when I say us, it's the sort of royal we, it's all life on earth. But is that true? Does our existence really tell us very much of anything? In science you can ask this sort of question in a Bayesian framework. Bayesian's probability with Bayesian analysis is a way of weighing evidence against models and gauging your confidence in the correctness of a particular model. You can ask the question in that way and the data that you have, it's really pretty simple. The data is that life has occurred here on the Earth, and it actually seems to have started up pretty early on in the Earth's history, not that long after the last final formation epoch of the planet. We need a few hundred million years of the planet settling down into something close to its present physical state. Is it that early start to life on Earth and the existence of life here in the big universe, is that evidence for what I've called a high abiogenesis probability? Is life going to happen pretty easily? Well, if you do this properly, mathematically, the answer, perhaps not too surprisingly, is well, not really, doesn't tell you anything. It doesn't tell you very much. It's one data point. Of course that should have told you all along that it wasn't going to tell you very much. The answer you get out is acutely dependent on the assumptions you make in the first-place, the prior that you put into this analysis. In fact, life could be very numerous throughout the universe. We could also still be the first example of life anywhere in the observable universe. There is no constraint on the onset. But what we do learn from this analysis and this is the crux behind everything I'm going to talk about this afternoon, is If you could just find one example of independent abiogenesis, one independent origin of life event somewhere, anywhere. It would change the statistics significantly. In fact, it would tell you that in a suitable environment, life is going to crop up once, at least once every billion years or so, which means that the universe would be full of life. I would characterize modern astrobiology as being that quest, that search for that independent, abiogenesis event, the independent origin of life event. Where can we look? Well, I'm going to very quickly summarize a number of things and I'm going to talk about some of them in greater detail. The earth is actually our first port of call to look for an independent abiogenesis event because a couple of possibilities on the earth, first is this idea of shadow life. I'm not going to go into that in any detail, but the idea of shadow life is what if there's some type of life here on the Earth, probably microscopic that just plays by different rules. It would actually be quite easy for that to exist and for us to not noticed it yet. I don't know what it is, but it could exist and that would be an independent example of life. The other possibility is that life started many times on Earth and in truly independent ways. Maybe it started over there and it started over there, completely independent of each other. That would also help us evaluate this probability, this universal probability of life occurring. Mars is also a great option. Mars is similar to the Earth in some ways and other ways it's completely radically different, but it is accessible to us and we could go and look for signs of past life on Mars. We could even go and look for signs of life on Mars today, and I'll circle back around to that. But one problem with the Earth and Mars [NOISE] is proving that you've really found something truly independent of our version of life, of our origin event, and that's in part because Earth and Mars have exchange material constantly over the last four billion years. Every time an asteroid hits Earth or Mars, it spews off chunks of matter into space that sit on orbits that eventually may cross the orbit of the other planet. We know there are bits of Mars on the Earth. There are almost certainly bits of the Earth on Mars. They may have been able to carry organisms back and forth. If you find life on Mars, it might be related to us. In fact, some people even claim that Mars is probably a better place to incubate life four billion years ago and that we're all Martians.