[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].
