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Transcript
1 Astrobiology Short Course Unit 1a: What Is Life? Have you ever really sat back and wondered, "What makes me alive?" Why do we think of something as peaceful as a rose bush as living but something as violent and active as our sun as non-living? Scientists have clear, concise definitions for many things, but scientists still argue about what living really means. Is it possible to come up with some simple tests or rules that let us know for sure if something is a living thing? "Living things grow" is a common idea. Sure — but so do crystals and volcanoes, and we don't usually think of them as alive. Also, some living things like bacteria stay about the same size their whole lives. "Living things move" isn't that great of an idea either. Mushrooms, lichens, and most plants pretty much stay put. We might do better with something like "living things eat." All living things seem to need energy, which they get from the environment — sometimes as food, though plants can get their energy directly from sunlight. Because there are so many ways of eating we often say that living things exchange energy with their environment. Also, all living things we know about can reproduce, that is, make copies of themselves in some manner. We also say they contain a genetic code they can pass on, which is like a "blueprint" for building new life. The amazing molecule called DNA can store so much information that this "blueprint" is placed in every cell of our bodies. It's the reason that a giant sequoia tree can grow from a tiny seed! While DNA seems to be the blueprint for life on our planet, there may be other ways of storing and passing on information between generations. Maybe somewhere there are aliens that have an even better way of storing information! All life that we know of is based on cells. Cells are small (microscopic) units surrounded by a membrane and having specialized functions. Again, there might be life somewhere in the universe that isn't cell-based, but we haven't found it yet! Tiny, microscopic cells are just the right size to exchange fluids and nutrients with the environment. Bacteria are well-suited to being one cell in size, but other organisms use cooperating sets of cells (tissues and organs) to perform more complex and specialized functions. And all of this complexity — the instructions to grow a heart, lungs, liver, skin, bone structure — is contained in the DNA in every cell of our body! Life is amazing. Every time we think we have it "figured out" we discover something new. We once thought life could not exist without oxygen and sunlight. We thought it could only exist in a very narrow range of temperature and acidity, and that there was no way life could survive for more than a few seconds in outer space. It turns out we were wrong! We'll talk next about "extremophiles" — organisms we've discovered that can live and thrive in environments that would kill most plants and animals instantly. 2 Sidebar: Think Like a Scientist When scientists try to define a term such as "life" or "living" they want a very precise definition. They wouldn't be satisfied with a definition that says "most living things act like this." Scientists want to define the necessary and sufficient requirements for life. A requirement sufficient for life means we know it can be alive. For example, something made of cells that reproduces and interacts with its environment is sufficient to define it as "alive." But is being made of cells necessary for life? Could there be something alive, somewhere, that isn't made of cells? Could a computer program be "alive" if it can adapt to its environment and reproduce itself? These are hard questions. Part of a scientist's job is to clarify language, and give us good, precise, trustworthy definitions that are reliable. This controversy continues today. A central dogma in science is that life is dependent on water. Water is the universal solvent in which energy can flow from one organism to another and from non-living to living matter. In fact, to date, all life is based on water. However, as new information was sent from the Cassini-Huygens mission in 2010, a new theory began to circulate about the potential for life in liquid solvents other than water. The chemical signatures on the atmosphere and on the surface of Titan suggested alternative and unusual chemistry that sparked ideas of possible life on this orange moon of Saturn. Titan has a thick atmosphere and liquid methane lakes. This result makes Titan the only place in our solar system beyond Earth known to have liquid on its surface. Activity: Take a few moments and write down your definition of life. This might take a few sentences. Save your definition. Later on in this course, we'll explore some living and non-living things, and you can see how good your definition is at distinguishing between the two! Activity: Ten Living Things, Part 1 Without thinking about it too much, make a list of TEN LIVING THINGS on a piece of paper. When you are done, go to Part 2 of the Ten Living Things activity to answer some questions. Activity: Ten Living Things, Part 2 Now, review your list of TEN LIVING THINGS and answer the following questions. 3 1. Did you enter any PLANTS? That is, complex living things that get their energy directly from the sun? 2. Did you enter any organisms that are TOO SMALL to see with the naked eye (i.e. microscopic organisms)? 3. Did you enter any organisms that could live in Antarctica, or any place on Earth that is frozen nearly all year long? 4. Did you enter any organisms that live underwater in ocean environments? 5. Did you enter any parasites, that is, organisms that depend entirely on another organism for survival? 6. Did you enter any pure carnivores, organisms that eat nothing but meat? 7. Did you include human beings in your list? There's a lot of diversity in life! Often we forget how many different types of life there are, because much of it is so different from us, including things too small to see. Check your list again to see if you entered any NON-LIVING things. Common non-living things that students often confuse with life include: water, sunlight, wind, fire, smoke, clouds, machines (including robots), or anything else that moves. Watch for these misconceptions! Unit 1a: Assessment 1. Which of these is the best evidence that something is alive? it moves it grows it reproduces it changes color 2. Which of these is NOT good evidence for something being alive? it reproduces it gives off odors it has a genetic code it's made of cells 3. All living things exchange energy with their environment in some way. True False 4 4. The complete "blueprint" of all the information needed to rebuild your body is contained: in specific places scattered throughout your body in the cells of your brain in your sperm/egg cells only in nearly every cell of your body 5. When many cells cooperate, they form ________ and organs. organelles tissues skin proteins Unit 1b: What are Extremophiles? By the 1960s, we thought we had the necessary conditions for life pretty much figured out. Based on what we knew then, life had to have water, oxygen, and sunlight available. Living things could survive freezing temperatures, but only for a little while; and no living thing could survive boiling temperatures. Life could exist in salt water, but not water that was TOO salty. And life could not exist in highly acid environments (below pH 6) or highly alkaline environments (above pH 9). The idea of anything surviving in outer space was just silly. Every living thing had to carefully protect its DNA; if the cell’s nucleus was destroyed, the information in the DNA was gone forever. We certainly hadn’t found all living things, but we knew where to look, and where we could safely assume no life could exist. We were dead wrong. Even before the 1960s, there were some clues that we might have underestimated life. In the early 1900s we depended on salt to preserve codfish — after all, no bacteria could live in a nearly pure salt environment. But much to the fishing industry’s distress, salt cod was spoiling. Somehow, bacteria were surviving and even thriving in the salt. And in the 1940s, acid-loving microbes were discovered in highly acid mine drainage sites like Iron Mountain in California. But it wasn’t until Thomas Brock discovered bacteria living in Yellowstone’s boiling-hot springs and geysers in the 1960s that we realized we had to totally rethink what life was, and where it could exist. Perhaps the most amazing revelation of all came in 1977, when undersea explorers Jack Corliss and Robert Ballard discovered “black smokers” — incredibly hot thermal vents — at the bottom 5 of the Atlantic Ocean. Here in the total darkness, under incredible pressure, in this boiling, toxic, deadly brew, they found life. Not just a little bit of life, but an entire rich and beautiful ecosystem. Take a few moments to watch Ballard talk about that day of discovery; it was the day that biology turned upside down, and all our biology textbooks had to be scheduled for a rewrite. Life is a lot tougher than we thought. Now we know that there are many forms of life that thrive in environments that we think of as extreme — salty, acid or alkaline, very hot or cold, poisonous, high or low pressure, and even radioactive. They have classifying names based on what environment they “love,” such as halophiles (salt-lovers), thermophiles (heat-lovers), acidophiles (acid-lovers) and so on. Most of them are single-celled organisms, but some are complex organisms like fish or worms. We’ve discovered creatures that can survive having their cell’s nucleus destroyed by radiation, and are somehow able to reassemble their DNA from shreds and scraps. We’ve discovered that certain insects can survive the vacuum of outer space for days. We’ve had to broaden our thinking, and our definition of life, to include the amazing diversity of the extremophiles. Sidebar: Think Like a Scientist Scientists are often wrong -- some would say, always wrong. The scientific goal is complete understanding, but we get there step by step. We use our best theories to predict and explain what we see, and when we find that something doesn't work, we change or revise the theory -- or sometimes throw it out altogether! Some people get angry or disillusioned with scientists because they "keep changing their story." Think about this, though: if scientists didn't change their story, we'd still imagine the Earth as flat and treat blood diseases with leeches! It's the ability to detect that you're wrong and revise your theories that makes science so powerful. Think about the photo at right, which is of Yellowstone National Park in winter 2010. The algae growing in this hot spring channel thrive at a pH between 1-4 (equivalent to battery acid), with an upper temperature of 56 degrees C (133 degrees F). Fascinating! But how does it do it? That is what this scientist wants to learn. At each step of discovery, an idea or theory is put forth, and a prediction is made. Experiments are designed to test whether the theory can be proven false. 6 Sidebar: Timeline of 20th Century Extremophile Discoveries 1920s - Salt cod spoilage mystery (halophiles) 1940s - Iron Mountain mine drainage mystery (acidophiles) 1956 - A. W. Anderson discovers D. Radiodurans (radiation resistant bacteria) 1960 - Takahara isolates alkaliphiles from indigo fermentation 1961 - Imre Friedmann discovers cryptoendoliths in desert rocks 1966 - Thomas Brock discovers Yellowstone hot springs thermophiles 1974 - R. D. MacElroy coins the term "Extremophiles." 1976 - TAQ Polymerase isolated, would revolutionize DNA studies 1977 - Carl Woese identifies Archaea 1977 - Robert Ballard discovers Atlantic thermal vent life 1981 - Hyperthermophiles in Iceland discovered by Zillig/Stetter 1993 - Tommy Phelps finds 100+million year old endoliths in oil deposit 1996 - First Archea genome sequenced 1997 - Methane ice worms discovered on Mexico sea floor Sidebar: Think Like an Alien On planet Xortus, the ninth planet from the star XerXerNix-5, lives a strange race of methanebreathing, acetone-drinking aliens called the Xorts. The average surface temperature on their planet is minus 80oC (-112oF), so liquid water would only show up in their laboratories. In fact, water is considered a deadly poison to Xorts. All life on planet Xortus is based on methane, which they consider the fundamental chemical of life. (By the way, based on recent discoveries of possible life signatures on Saturn's methane-rich moon Titan, this may not be too far-fetched!) A Xort scientist has recently pointed its telescopes and sensitive instruments directly at our star, and noticed our planetary system including Earth. Would this scientist guess that life exists on our planet? If so, can you think of any clues the scientist might look for? Would we be considered "extremophiles" by this scientist? Activity: Extremophile Matching Game Match the extremophile to the extreme! See if you can guess, based on the name, where these kinds of extremophiles might call "home." 7 Unit 1b: Assessment 1. The discovery that life can exist in extremes of temperature, saltiness, acidity, and pressure was made: in the Middle Ages around the time of Darwin in the mid-1900s only in the last decade 2. No living creature can survive extreme damage to its DNA. True False 8 3. Corliss and Ballard discovered lifeforms at the bottom of the Atlantic near volcanic vents called: hot springs lava tubes gushers black smokers 4. An organism that loves salty environments would be called a halophile. True False 5. Thomas Brock discovered extremophile bacteria in the hot springs at: Yellowstone Salt Lake Hot Springs, Georgia Reykjavik, Iceland Unit 1c: Where are Extremophiles Found? When we talk about life in extreme environments, you might think these life forms are rare, because we think of extreme things as being uncommon. Remember, though, what we call extreme just means places where we couldn’t live. Humans (and most plants and animals) only thrive in a narrow range of temperature, pressure, salinity and pH. There are a lot more extreme environments than one would think. In fact, extremophiles are present all around us. Most of them are single-celled organisms and many are in the domain Archaea. Archaea are similar in appearance to bacteria, but they have many differences in their DNA. In fact, scientists now believe that Archaea are the oldest life-forms on the planet – no surprise really, since the cooling Earth would have been a very extreme environment. So, if you wanted to find some extremophiles, where would you look? One place might be under your feet. Endoliths are organisms that can live and thrive in rock, feeding on minerals, and they have been found over a mile deep in the earth’s crust. Another place to look might be inside the nearest cow. You may have heard that cows “fart and burp” methane gas, but you might not know that there are organisms that love those methane-rich environments. Methanogens are organisms that produce methane gas and are commonly found in cow’s intestines, as well as in swamps and oil deposits. 9 Put on your fur parka and head to the frozen Arctic wasteland, or south to the equally frigid Antarctic ice sheet, and you might think you’d be alone. But in the pressurized ice here are tiny cracks filled with salt water, and – you guessed it – living things. Psychrophiles or cryophiles are the names given to “cold-loving” organisms, many having cells filled with “antifreeze” solutions similar to what you might put in your car’s radiator. You’ll even find cryophilic fish swimming underneath the permanently frozen sea ice. You might want to warm up now with a trip to a nice hot spring. Yellowstone has plenty, at temperatures upwards of 88°C (190°F). That might give you and me third-degree burns, but thermophiles are thriving in this environment, feeding off ammonia and sulfur. If you want the REALLY hot springs, you might take a submarine journey down to the pitch-dark bottom of the ocean, where “black smokers” vent sulfur-rich liquids at over 150°C (300°F). Not only will you find Archaea living in these vents, but huge, thriving ecosystems with tubeworms and crab-like creatures are built around them. Even without sunlight, life is able to thrive using a process called chemosynthesis (like photosynthesis, but based on chemical energy rather than sunlight). You and I use chemosynthesis, too — we don't need sunlight directly — but we depend absolutely on photosynthesis in plants for all our food. We never imagined that a whole ecology could be built without a single ray of sunlight. Now if you're feeling the need to dry off, you could head out to the barren salt flats around Salt Lake City or San Francisco Bay. Here, the water at lake's edge is so salty that it is crystallizing. But what are all those amazing colors? Sure enough, we're looking at life again. Halophiles, saltloving organisms, still need water to live, but can tolerate large amounts of salt mixed in. Is there anywhere we can travel where we DON'T find life? Well, since this is about ASTRObiology, I guess we could put on a space suit and take a quick trip into outer space! Let's look at three places of interest in our own solar system: Titan, Europa, and Mars. Titan is the largest moon orbiting Saturn. It is very, very cold — about -178°C (-288°F) — but it actually has lakes and oceans on its surface. These are made of liquid methane, not water. Titan also has an atmosphere, mainly nitrogen and methane gas. Now that we know there are methaneloving extremophiles, it opens the possibility that we could someday find life on Titan. In fact, some recent discoveries from NASA's Cassini probe are causing excitement about this mysterious moon. Europa is not the largest of Jupiter's moons — that honor belongs to Ganymede — but it may be the most interesting, at least to astrobiologists. One reason is that recent probes have shown strong evidence of vast oceans of liquid water just underneath the icy surface of this moon. Yes, it's cold, and yes, it's dark. But that hasn't stopped life at the bottom of the Atlantic. Could we find life deep within Europa's oceans? Time will tell… Mars has certainly caused a lot of excitement in recent years. Its relatively close orbit has allowed us to send robotic "rovers" to the surface, enabling scientists to look much more closely for signs of life. So far, there's no convincing evidence. BUT we did find confirmation of water ice near the Martian surface, and the soil of Mars is fertile and nutrient-rich. The surface features of Mars strongly suggest that this planet may have once had oceans, lakes and rivers. Was there 10 life on Mars at that distant time? Could it even be there today, lurking under the surface? We don't know, but rest assured we'll be sending more robots, and maybe even people, to this tantalizingly close planet. Sidebar: Additional Resources World Map of Extreme Environments Slide Show of Extremophiles: The World’s Weirdest Life How Extremophiles Work Activity: Extreme Venn Drag three of the environmental conditions in the upper left onto each of the three colored intersecting circles. In the blanks at the bottom, type a name for the environment at each of the intersections. For example, you might label the intersection of "Dark" and "Cold" as "Siberian Winter," and the intersection of all three as "My Refrigerator." When you are done, hit submit to see your environments on the Venn diagram. You can hit reset to start over. Having trouble? Click on hints at the bottom, or use the Internet to help find "real" environments like this! Do a little more research on extremophiles -- are there any known to exist in your "overlap" environments? 11 Unit 1c: Assessment 1. Which statement is true of extreme environments? they are more common than environments we'd call "normal". they are very rare in nature they are hostile to all life they hold no interest for life scientists 2. Organisms that thrive inside rock itself are called: halophiles endoliths cryophiles lithophiles 12 3. Organisms that produce methane-rich environments (found in swamps and cow intestines!) are called: methoglans methanocides methanophiles methanogens 4. Without light, organisms can't perform photosynthesis, so living communities cannot form. True False 5. All extremophiles are single-celled organisms. True False Unit 1d: What Can Extremophiles Teach Us? Biologists get excited about the discovery of ANY new living things, but extremophiles have caused more excitement, and more radical changes in science, than any other forms of life. Why? After all, most extremophiles are single-celled creatures, measly microbes. What is it that makes them so fascinating to scientists? The short answer is DNA. Many single-celled extremophiles are in the domain Archaea. The DNA of Archaea is quite different from common bacteria. Analyzing DNA is rather like looking at ancient texts written in an alphabet, and reading the “alphabet” of Archaea is like reading an ancient Phoenician alphabet – simpler in many ways, with strong evidence that it was an older form of life. Archaea, as its name suggests, is very old - perhaps as old as the first bacteria, but certainly much older than even the simplest multi-celled organisms. As we find out more about Archaea, we are gaining insights into how life may have begun on our planet – and perhaps how life might begin on other planets. In addition to what extremophiles are teaching us about the origins of life, we’re also learning of practical applications for medicine and genetics. For example, Yellowstone’s famous extremophile bacterium Thermus aquaticus was found to produce an enzyme called Taq polymerase, which can quickly make millions of copies of DNA molecules at temperatures above normal life conditions. It turns out this is exactly what was needed in the laboratory to copy DNA for research. Around 1983, a technique called PCR (polymerase chain reaction) 13 was developed using this enzyme to copy DNA in a test tube. It is now used in DNA “fingerprinting” for paternity and forensics, genetic medicine, and thousands of other uses. Pioneer genetics researcher Craig Venter, along with many other research teams, are trying to find ways to construct new lifeforms that could, for example, turn excess carbon dioxide in the atmosphere into fuels, or clean up oil spills, or selectively attack cancer cells. Laboratory genesplicing techniques were able to build short sections of DNA, but not the tremendously long sequences needed by a "real" organism. Again, extremophiles came to the rescue! An extremophile bacterium called Deinococcus radiodurans was found to be able to reconstruct its DNA after having it “shredded” into thousands of fragments. Venter was able to harness this amazing ability and splice together thousands of smaller DNA fragments, producing the first true “artificial lifeform." Gaining control over these basic mechanisms of life, even though it has risks and ethical issues, could open up vast new possibilities in energy and medicine. Does life exist elsewhere in the universe? More and more scientists are convinced that we’ll soon find the answer to be YES. It's not likely to be "little green men" from Mars, but we may well find single-celled lifeforms somewhere other than Earth. Part of the reason is that our discovery of extremophiles broadens the range of conditions where we know life can exist. We now know that life can exist without oxygen, without sunlight, and perhaps even without liquid water. Even complex, multicellular organisms have been found to be amazingly hardy. During a 2007 NASA mission, tiny animals called Tardigrades, or “water bears,” were found to be able to survive after ten days in the vacuum of outer space. They can also survive being dried out for decades, cooked past boiling, zapped by normally lethal radiation, or squeezed at six thousand times air pressure. Now that’s tough! Sidebar: Archaea or Archaeabacteria? The "third domain" of life was discovered in the 1970's by biologist Carl Woese. He originally thought these organisms were a subclass of bacteria -- after all, they were single-celled and didn't have a nucleus, making them prokaryotes, just like bacteria. So he came up with the division of bacteria into eubacteria and archaeabacteria, which is what we still find in many life science textbooks. However, when classifying organisms, it's not just what you look like that counts; it's what's in your DNA. Woese eventually decided that the DNA of this new "bacteria" was so radically different that it was not bacteria at all, but an entirely new domain of life. We now recognize three "Domains" of life -- Bacteria, Archaea, and Eukaryota. The “Kingdoms” -- plants, animals, protists, etc. -- fall under these Domains, mostly under Eukaryota. Bacteria and Archaea are the prokaryotes, cells without a nucleus. The domain Eukaryota, or eukaryotes, all have cells with their DNA contained in a nucleus. Some eukaryotes, such as the amoeba and paramecium, are single-celled; but many more are multi-celled, including plants, fish, insects and mammals. In fact, without a good microscope, it's unlikely that we'd know anything other than multicellular eukaryotes! 14 Activity: Space Frankenstein We're looking for lifeforms on Mars, Europa, and Titan, and you're in charge of a top-secret genetic engineering project to try to "simulate" life that might be able to survive on these planets. Our theory is that if we can create a "Frankenstein" extremophile that could survive in these conditions, we can learn what clues to look for as we study these planets and moons for traces of life. Your job is to try to combine genes from two different organisms to create a new organism -- one that "has what it takes" to survive in these extreme environments! We've described what we know of the three environments below, and given you a list of extremophiles to choose from. Which ones would you pair up for each environment? 15 Unit 1d: Assessment 1. What quality might make extremophiles so interesting to scientists? they have different DNA they have remarkably different survival mechanisms they can provide "raw material" for new inventions all of the above 16 2. The study of extremophiles led to a whole new "Domain" being added to the base of the tree of life. This domain is called: Extrema Bacteria Archaea Animalia 3. What quality made Deinococcus radiodurans so interesting to artificial life research? it produced TAQ polymerase it could resist extreme heat it could reassemble its own DNA from scraps it glowed under UV light 4. TAQ polymerase from hot springs bacteria is used in the ___ process for DNA analysis and fingerprinting. TAQ MMR PCR NMR 5. Tardigrades, shown to be able to survive in outer space, are single-celled creatures. True False Unit 1: Resources NASA - What is Life? Q&A Website from NASA Exploratorium: Origins Informational website from NSF Extreme Ecosystems Informational Website from NASA 17 Windows to the Universe - What is Life Informational Website from the National Earth Science Teachers Association. Windows to the Universe - Extreme Environments Informational Website from the National Earth Science Teachers Association. NASA Astrobiology website NASA web page / news blog Astronomycast Podcast - Astrobiology Astronomy Cast Podcast with transcript. What is Life - Space.com - A New Theory Informational website from space.com NOVA - Cave Extremophiles Interview with researcher from NOVA X-treme Microbes (NSF) Interactive Website from NSF. Unit 1: Lesson Plans and Activities Defining the Habitable Zone Grades 5-8. In this activity, students explore the orbital characteristics a planetary home needs to support Earth-like life forms. Lesson plan from NASA MSU-Bozeman CERES project. Who Can Live Here? Life in Extreme Environments Grades 5-8. Students explore the limits of life on Earth and examine the possibility of life on other words. Lesson plan from NASA MSU-Bozeman CERES project. The Rare Earth - How Rare is Earth-Like Life? Grades 9-12. How special are the circumstances that have allowed complex life, like animals and plants, to develop on Earth? In this activity students systematically investigate the time frame for complex life to develop on Earth. Lesson plan from NASA MSU-Bozeman CERES project. Lotto or Life - What are the Chances? Grades 6-9. A NASA Goddard Space Flight Center lesson plan that encourages students to compare the likelihood of intelligent life existing elsewhere in the Universe and winning the lottery. Microbial Zoo Grades 9-12. In this activity, students will explore the extreme conditions in which life is known to exist in on our own planet, then examine similar environments on other planets in our solar system. Lesson plan from NASA MSU-Bozeman CERES project. 18 NASA Astro-Venture Grades 5-8. Interactive, multimedia Web environment where students role-play NASA occupations, this Astro-Venture is a Biology Training Module in which students change the biological features of Earth and observe the effects. Students will also explore how these features work together to help make a planet habitable to humans. Astrobiology in Your Classroom (NASA) Grades 5-8. This Educator Guide is full of hands on activities that lay the conceptual groundwork for understanding questions fundamental to the field of astrobiology. These activities enable students to examine the nature of life, what it requires, its limits, and where it might be found. Created by Cornell University Department of Astrobiology. TERC Astrobiology Curriculum Grades 6-12. This is a middle and high school curriculum developed by TERC that teachers must pay to purchase. However, free sample activities on topics such as the history of life on Earth and habitability are available.