 Greetings and welcome to the Introduction to Astronomy. In this lecture we are going to talk about astrobiology or biology in space and we'll talk about life and what the possibilities of that are. So what is important for life? Well, some things that are important are specific elements that are needed. The Big Bang gave us two elements, hydrogen and helium, and that's it. So that was the only elements created in the Big Bang. Other elements were created in stars. We also need organic molecules. Now organic does not mean living, but organic molecules are molecules based on carbon. So where do these come from? Well, we have to have had stars first to produce the carbon through nuclear fusion and then expel it back out into space. We also tend to think we need liquid water and there's only one object that we know of currently with liquid water on its surface and that is our Earth. So other objects may have had liquid water in the past and likely did such as Mars but others have never had liquid water on their surface. Now, let's take a look about some of the things about what is special about Earth. Well, we're not really unique and when we started out the class we considered Earth was the center of the universe. The Earth was the center of the solar system and we then moved out and put the sun at the center of the universe and then we thought maybe we were at the center of the galaxy and then so we've sort of moved ourselves away from that as we learn more and more. So we're not at the center of anything here. We are just one planet among many and we have found habitable planets around other stars. We have seen that when we looked at the discovery of exoplanets. Now, one thing to mention here is to talk about the Fermi Paradox. Now, this was given by Enrico Fermi many years ago and it was a thought that if other civilizations formed where are they? Why do we not see other civilizations here? And the idea is that if civilizations form we would expect them to be able to expand outward. Now, how long would that take? Well, if we have a civilization forming on one star here and we give them some time to evolve and to be able to colonize nearby stars how long would it be before they colonize, say, two nearby stars? Well, maybe let's just pick a number and let's just say it takes them a million years. Let's pick a very long time. How long will it take us to colonize the nearby stars? Well, a million years from now should we have done that and that's quite possible. And then you can keep this up and then after another million years you would have each have colonized more stars and then another million years each of those civilizations colonizes stars and you might also expect that some of these would go a lot faster because as you have colonized a star you know you have far more technology than that original civilization but in just a few million years it looks like many stars would be colonized in a billion years the entire universe let's say the entire galaxy would be colonized in that case just spreading out like this and it would not take a very long time and all of these civilizations should be there so where are these other civilizations? Are we the first? Do other civilizations not communicate with us because we're not technologically advanced enough yet? Or are we the only civilization out there? So let's look at what we mean by astrobiology we want to look at four signs of life and different types of materials in space now the building blocks of life are the amino acids that make up our DNA and we find those in meteorites so they're not confined to Earth we can't find them elsewhere in the solar system the mercheson meteorite is one example shown here that has found amino acids which are not part of Earth life so other types of amino acids that are not part of life on Earth and are definitely from outside now that does not mean life, those are just the building blocks they have not combined into any kind of life yet even at a very simple level we also find organic molecules in molecular clouds such as the one shown here and regions of star formation so these molecular, the organic compounds again this is material based on carbon so they're very common in the universe and in fact they're very easy to create and this was done in the 1950s the experiment was done to simulate the primordial or early atmosphere of Earth now the early atmosphere would have consisted of things like water, methane, ammonia and hydrogen so that's what was put in here sparks to be energy and lightning strikes and then material was flown, water was heated goes through the piping into this chamber cooled off and then a trap here to catch any material that was found so subjected to heat, electrical discharges and the material that was condensed out had complex organic molecules including amino acids now again that is not life it did not create any kind of even very simple life but it did show that the basic building blocks of life could have formed easily in the conditions present on early Earth so does that mean there could be life elsewhere if these building blocks of life are very common and that is a very good question so the problem is that it is a very big step from organic compounds which are very common to life so it's a big big step from even the most complex chemical compounds to the very simplest biological compounds what was this early Earth like well here we might have seen what Earth looked like very early on first of all we had impact sterilizing the surface and finally they slowed and the oceans began to form which contained these organic molecules we see some of the earliest signs of fossil life going back about three and a half billion years now remember Earth is about four and a half billion years old so within the first billion years of the Earth's formation life had formed and we see this in things called stromatolites which we see some here off the coast of Australia and they're again very simple creatures that build themselves into colonies here in a way somewhat like coral that forms and there are living ones there still exist today and there are fossilized remnants of these that we find going back almost to the origin of Earth now that's just fossilized life that we see it's quite possible that other life could have existed even earlier so it looks like life formed on Earth very quickly after Earth formed again the big thing we need to do is to make that jump from chemical to biological evolution and that is a difficult thing the DNA that makes up all of our contains all the information about any organism including ourselves and is able to replicate itself now we also have RNA, ribonucleic acid which is a little simpler and now helps aid in the flow of genetic information and may have been a step in between forming going from those complex chemical compounds to those very simple biological compounds it's a big jump even though there's little difference between them actually making that jump from chemical to biological is a big big step now what else do we need for life well we tend to think we need oxygen and we have to realize that for much of Earth's history there was very little oxygen in the atmosphere oxygen began to accumulate about 2.4 billion years ago but it was at a very low level so if we look at the chart here we really see that it hasn't been until the last half billion years or so that we started to get significant levels of oxygen in the atmosphere and it's varied over time but that means that if you were to take a time machine back into history of Earth make sure that you bring some kind of oxygen to be able to breathe because for most of Earth's history this goes back 1 billion years but remember we go back 4.5 billion years and the oxygen never got more than this at that point so there was no oxygen or very little oxygen in the atmosphere and in fact we needed the oxygen because that helped with the development of the ozone layer ozone is oxygen with three atoms as compared to the oxygen that we breathe which is O2 oxygen atoms together now ozone is also a pollutant if it's on the surface of Earth but up in the upper atmosphere ozone protects because it absorbs the ultraviolet light which allowed life to move on to land so if we think about that also for vast majority of Earth's history there was no life on the land and that doesn't mean just animal life, plant life, anything that all life for the very early history was in the oceans so what do we mean by a habitable environment? well we tend to think of what we need is based on what we are used to hear on Earth there's also possibilities science fiction will do things like silicon based life or life that is not based on water but they're really just speculation could they exist? maybe we'll find some maybe we'll be able to get out there at some point and we will find some kind of life that exists and that will be a big jump maybe we'll see that oh it's very easy to have life based on one of these right now we don't see it water as a solvent we think water is very important certainly you need some kind of liquid to facilitate the biological and chemical reactions that are needed and water is only liquid in a very narrow range of temperatures and pressures so we do not see water liquid all over the place we need very specific range could you use something other than water? it's possible Titan has methane on its surface however the temperatures are also so cold that chemical reactions would not go very fast now let's take a look at carbon carbon is the basis of life on Earth and it's important because it forms multiple bonds and can form long chain molecules such as the one shown here so the carbon is very good at bonding together it can make four bonds per each carbon atom and that allows for longer chains than other atoms are able to create we also look at things like hydrogen nitrogen, oxygen, phosphorus and sulfur which combined with this are kind of the biogenic elements are they required for life? again that's a good question but maybe it's just our bias because that's how things work here on Earth and it's hard to imagine life existing without these how about extreme conditions? there are a human life specifically has very strict limits we have to have narrow ranges of temperature in pH otherwise it will kill us very high temperatures or very low temperatures will kill a human and many animals and plants however there are creatures known as extremophiles which can exist and even thrive under very extreme conditions in fact we have things like thermophiles which can exist at high temperatures the boiling point of water we wouldn't survive very long in boiling water psychrophiles, low temperatures down to 25 degrees below zero Celsius so extremely cold temperatures acidophiles, alkylophiles which exist at high and low pH levels and others that can tolerate high salt high pressures or even high levels of radiation so while human life has very strict limits other types of life can actually survive and even thrive in very unusual conditions and that's kind of like the little tardigrade shown here highly magnified it's a microanimal discovered back in the 1700s which can exist in a wide variety of conditions it's not affected by extreme temperatures pressures, radiation, dehydration, starvation and has even been tested and can survive in the vacuum of space for up to 10 days so again we couldn't survive very long at all seconds in the vacuum of space this can survive for days in the vacuum of space so life is also very very hardy at least certain types of life are very hard to eliminate so let's go ahead and finish up this section with our summary and what we've looked at is life as we know it based on carbon and water so that's what we look for when we're looking for life elsewhere in the universe we know that life on earth formed very early within the first billion years and maybe even earlier and we looked at organisms that can survive extreme conditions including the vacuum of space for a limited time so that concludes this lecture on astrobiology we'll be back again next time for another topic in astronomy so until then have a great day everyone and I will see you in class