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Organic Molecules • Many Other "Fuzzy" Cases

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Organic Molecules • Many Other Searching for Life in the Outline Solar System... and Beyond! • What is Life? • Life in Extreme Environments • The Searches for Extrasolar Planets and Extraterrestrial Intelligence (SETI) Prof. Jim Bell Cornell University Astrobiology But first...What is Life? The question is philosophical, Astrobiology (sometimes called Exobiology) is • • poetic, spiritual, intangible... the study of life in the Universe • Origin of Life but also scientific! • Distribution of Life To find life we must define Ultimate Fate of Life • • what we seek... • Astrobiology today is an extrapolation from the • "Intuitive" definition: one known example (Earth life), using the basic • “I know it when I see it” principles of chemistry & physics and observing • Not very rigorous the Universe around us... • Applies only to Earth life? What is Life? Attributes of Living Systems... • A more rigorous definition: • Rather than defining life, can we describe it in • Something is alive if it has the ability to ingest terms of specific attributes? nutrients, give off waste products, & reproduce Life has at least two unique attributes: • But what are nutrients? • What are waste products? • (1) A living system must be able to reproduce, to mutate, • Is growth important? (mountains "grow"...) and to reproduce its mutations • Clearly the definition must acknowledge that life (2) A living system must be able to convert external is hard to define and that there are likely to be energy sources into useable internal energy sources exceptions to any rules proposed... But even this gets dicey... The Essential Requirements • There are systems with one attribute but not both • Liquid Water • "Medium" for the chemistry of life (mobility, nutrients) Chemical Reactions CO2 + sunlight --> CO + O Stable over wide range of temperatures • H O + sunlight --> H + OH • • CO2 "reproduces" 2 • Unique freezing properties help maintain stability • But it's not alive! CO2 + OH --> CO2 + H • Complex organic compounds don't dissolve in water! • Crystals • Source of Excess Energy • "reproduce" in regular patterns, get distorted (mutated) • Sunlight (photosynthesis) • Chemical (oxidation) • Fire • Thermal or geothermal... • Uses "nutrients", converts energy, "grows", "reproduces", ... • Source of Organic Molecules • Many other "fuzzy" cases... • C, H, N, O, P, S combined in both simple and complex ways • Mules? A virus? Computer programs? Robots? • "Simple" organic molecules appear to be abundant out there… Origin of Life on Earth? "Panspermia" Key Questions: • • Swedish chemist Svante Arrhenius proposed in 1908 that life is ubiquitous in the Cosmos and that "spores" or the (1) Did life originate on Earth or in space? seeds of life were delivered to Earth essentially by accident (2) If life originated on Earth: • No attempt to explain how life originated, only how it got to Earth (a) What were the conditions like on early • How did the "spores" get off other planets? (impacts?) Earth that made possible the origin of life? • How did the "spores" survive harsh interstellar radiation? (b) Did life originate on or near the surface, • More recent variation: "intentional" panspermia below the surface, or in the oceans? • Life was planted on Earth by space travelers • Popular among science fiction fans and conspiracy groupies • Still doesn't explain how life originated though... Organic Molecules in Meteorites Organic Molecules in Exotic Places Some complex organic molecules (molecules • !Complex organic molecules have also containing carbon) have been found in some of the most primitive carbonaceous chondrite been found or inferred to exist in: meteorites –Interstellar molecular clouds –Comets • Alkanes, benzene, paraffins, amino acids, … –Interplanetary dust particles –Some dark asteroids, rings, & planetary satellites Glycine: C NH O Benzene: C6H6 2 5 2 –Some other “anomalous” meteorites (e.g., ALH84001) !Did life on Earth originate from raw materials brought in by the early "rain" of debris from asteroid, comet, and cosmic dust impacts? The Miller-Urey Experiments Could Life Have Originated on Earth? (early 1950s, U. Chicago) • Hypothesized environment of the early Earth: Heating of interior, release of volatiles • • Water = primitive ocean H2, H2O, CH4, and NH3 • • CH4, NH3, H2 = primitive • H2O forms liquid ocean at Earth's P,T atmosphere • NH3 dissolves in water • electrical discharge = Result is a highly-reducing atmosphere lightning • • cycling through ocean... • H2, CH4 abundant Little if any free O • 2 • RESULTS: - complex organic molecules Can simulate this environment in the lab... - simple amino acids! • - life's building blocks! Making Primordial Soup Life on Earth Life on Earth • The Miller-Urey experiments were perhaps too • Very soon after the early Earth simplistic, but they demonstrated that the interactions of cooled and the impact rate slowed, liquid water, natural energy sources, and organic life appeared molecules leads to the production of complex organic • How? No one knows... molecules • Miller-Urey and more than 50 years • Even if the Urey/Miller process was not efficient enough of subsequent experiments have not to produce large quantities of organics, remember that been able to reproduce the result organics formed elsewhere were still being delivered to • Life has slowly increased the the early Earth by impacts... amount of free O2 in Earth's • The building blocks of life are abundant in the Cosmos! atmosphere over time • But how did the building blocks become alive ??? • Atmosphere is in disequilibrium Jakosky (1998) Starting Simple... Complexity is rare... • Life on Earth started simple • A census of life on Earth today or 3 billion years • Most life on Earth remains simple ago would reach the same conclusion: life on • All life on Earth is similar at a basic level Earth is dominated by simple bacteria! "Tree of Life" for (early Earth) Earth, based on similarity in RNA sequences among all life forms (past and present) on this planet (Woese, 1987) Gould (1994) ...and Accidents Happen! Some Big Questions • Evolution towards more complex life • Has this happened forms is not necessarily inevitable elsewhere? • bacteria are very efficient life forms... • in the solar system? External, even random forces play a role • in the Galaxy? • • in the Universe? – e.g., Gould's theory of "punctuated equilibrium" Starting over again with the same initial • Can we use our knowledge of the formation and • evolution of life on Earth to make predictions about conditions, could the experiment be repeated? the nature, distribution, and abundance of life "out • Would life form at all? (hmm...) • Would evolution follow the same path? (probably not) there" ? • Should we seek simple life, or complex life? Life on Earth Life in • Life developed early on the Earth Extreme • Conditions have not always been ideal... Environments • Changing atmospheric chemistry • Large-scale variations in climate • Active geology • Impacts • The result of life's adaptability to these variations is a dizzying array of diversity Extremophiles PROKARYOTES Life in Extreme Environments! • Evidence of the diversity of life is provided by groups of micro-organisms From permafrost to hot springs knows as extremophiles (lovers of • extreme conditions) From battery acid to salty lakes PROKARYOTES • • These life forms occupy niches of: • Deep under the ocean • Extreme temperature • Life relies on geothermal energy Extreme acidity • Deep under the ground • Extreme salinity • Life using geochemical energy • Greatest range: prokaryotes PROKARYOTES • • Simple, single-celled organisms • Some organisms have even • Substantial range: eukaryotes survived long-duration exposure • More complex, nucleated, and/or to the vacuum and radiation of space multicellular organisms Nealson (1997) Life Elsewhere in Our Solar System? Life on Mars? • The enormous range of diversity and ruggedness of life on Earth has only recently been recognized • Mars preserves clues that its climate may once have • The idea of simple life beyond Earth is not as crazy been very different... as it used to be! • And that there is still a substantial (?) inventory of water • We can make a "short list" of places to look: at or near the surface... • Mars • And that there were abundant volcanic, impact, and/or • Europa geothermal heat sources... • Titan • Liquid water, heat sources, organic molecules... the • Enceladus requirements for life as we know it! • And there may be more that we could add... Evidence of Life on Mars Evidence of Life on Mars from a Meteorite? from a Meteorite? • A small number (~50) of meteorites are thought to • Four pieces of evidence presented by scientists have come from Mars that ALH84001 preserves signs of past life on Special one: ALH84001 Mars: • • Carbonate minerals: precipitated from a • Found in Antarctica in 1984 once thicker, warmer, atmosphere? • Thought to be a sample of ancient Martian crust: • Magnetite grains: similar in shape to radiometric age around 3.5 billion years magnetite formed bacterially • Cosmic ray exposure indicates ejection from Mars • Complex organic molecules: around 15 million to 20 million years ago specifically PAH molecules • Segmented, "bacterial" shapes • Outer chemical evidence indicates that it fell to Earth about 13,000 years ago Landmark paper published by McKay et al. (1996) Science, 273, p. 924 But Much Skepticism! The Real Message of ALH84001... • Whether or not ancient fossil microbes actually • Is the rock from Mars? exist in this Mars meteorite may be secondary Was it contaminated by Earth
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