Lecture 17 - Life on the Edge - PDF Document

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  1. Lecture 17 - Life on the Edge Lecture 17 Life on the Edge Astronomy 141 – Winter 2012 This lecture is about the extremes of life on Earth. Extremophiles are organisms adapted to extreme environments. What are the limits of life on Earth? Can there be life without liquid water? Typical conditions on Earth today are comfortable for typical forms of life Average Temperature 20 to 36°C (4 to 97°F) Pressure 1 atm (sea level) to 0.5 atm (5500m) Salinity Oceans are 3.5% salt Acidity Neutral (pure water) to slightly alkaline (sea water) Radiation Low background: 0.003 Joules/kg/year Location Land or Sea Astronomy 141 - Winter 2012 1

  2. Lecture 17 - Life on the Edge Extremophiles are organisms adapted to living in extreme environments. Most are prokaryotes (bacteria and archaea) Some are eukaryotes and simple animals (tube worms) Overall they may constitute 1/3 to 1/2 of Earth’s biomass Could have been the first forms of life on Earth. High temperatures are bad for most organisms Heat degrades chlorophyll, stopping photosynthesis Heat decreases the solubility of CO2and O2in water Heat denatures proteins, causing them to stop working Thermophiles are organisms that thrive at high temperatures (>45°C) Found in hot springs and deep-sea hydrothermal vents Have proteins & enzymes that work at high temperatures Chemoautotrophs Chemosynthesis via oxidation of hydrogen sulfide or methane Pyrolobus fumarii Astronomy 141 - Winter 2012 2

  3. Lecture 17 - Life on the Edge Were Thermophiles the first forms of life on Earth? The earliest life was prokaryotic archaea Prokaryotes tend to be more heat tolerant Deep hydrothermal vents are isolated from the harsh surface of the young Earth Cold temperatures are bad for most organisms Freezing damages cells (superosmosis) Cold increases viscosity, limiting mobility of nutrients & wastes Cold proteins and enzymes get stiff, inhibiting their function Psychrophiles are organisms that thrive at low temperatures (<15°C) Found in glaciers, arctic ice, snow, & soil, and deep oceans Have flexible enzymes and proteins that act like antifreeze Some are eukaryotes that live by photosynthesis (snow algae) Desulfofaba gelida Astronomy 141 - Winter 2012 3

  4. Lecture 17 - Life on the Edge High salinity (too much salt) is bad for most organisms High osmotic pressure desiccates (dries out) cells by drawing out water. High salinity promotes protein aggregation (salting out), disrupting Function. High Salinity limits the availability of oxygen for respiration. Halophiles are organisms that thrive in high concentrations of salt Live in water with 10x the salinity of the oceans Dead Sea & Great Salt Lake Extra ions reduce osmotic pressure, stopping desiccation Implications: Salt seas on the early Mars & present-day Europa? Dunaliella salina The Acidity of an aqueous solution is measured by its pH pH=0 Battery Acid pH=1 Stomach Acid Low pH solutions are acidic (takes up electrons) pH=2 Lemon Juice pH=3 Orange Juice pH=4 Tomato Juice pH=5 Black Coffee High pH solutions are alkaline (gives up electrons) pH=6 Urine, Saliva pH=7 Pure Water pH=8 Sea Water pH=9 Baking Soda High acidity can destroy proteins and DNA or inhibit their function. pH=10 Great Salt Lake pH=11 Windex pH=12 Soapy Water pH=13 Bleach pH=14 Drano Astronomy 141 - Winter 2012 4

  5. Lecture 17 - Life on the Edge Acidophiles are organisms that thrive in highly acidic environments Survive in pH  2 (lemon juice to battery acid) Some efficiently neutralize their cellular interiors Other acidophiles have evolved acid-stable proteins. Ferroplasma acidarmanus Ionizing Radiation is hazardous to life DNA is susceptible to radiation damage: Minor Damage  self-repair Lethal Damage  cell death Non-Lethal Damage  mutation Radiation Dose = Energy absorbed per kg Medical X-ray: ~0.002 Joules/kg 10 Joules/kg is lethal to humans 60 Joules/kg kills E. coli bacteria Radioresistant organisms can survive high doses of ionizing radiation Deinococcus radiodurans can survive doses of 5000 Joules/kg Can absorb up to 15,000 Joules/kg with 37% viability Has very efficient DNA repair and carries 4 to 10 copies of its genome Deinococcus radiodurans Astronomy 141 - Winter 2012 5

  6. Lecture 17 - Life on the Edge Endoliths are organisms that live inside rocks & between mineral grains Found as deep as 3 km below the ground. Most are chemoautotrophs Reproduce maybe once per century Total biomass in endoliths could exceed all surface life! The Atacama Desert of northern Chile is the driest non-arctic place on Earth Virtually sterile desert 100 times more arid than California’s Death Valley. In a double rain shadow from the Andes and coastal mountains. No rainfall recorded in some regions for the past 400 years! Free of glaciers for the past 1.8 Million years. A 2003 study replicated the Viking 1 & 2 Mars life search experiments in the Atacama No culturable bacteria were found down to 10cm Two samples had no DNA A later study found viable bacteria at 30 cm depth Life can exist even in the driest environments as long as there is at least a little liquid water. Astronomy 141 - Winter 2012 6

  7. Lecture 17 - Life on the Edge Studying the extremes of life informs our search for life elsewhere in the Universe. The existence of extremophiles greatly extends the range of possible environments for life. Extremophiles may have been the first life-forms on Earth. No organisms are known that can survive without liquid water. Astronomy 141 - Winter 2012 7