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The Future of Life on Earth Over the Next Few Billion Years Jack O'Malley-James The Future of Life on Earth Over the Next Few Billion Years Jack O'Malley-James Two main questions Why are astrobiologists interested in the future of life on Earth? What happens to Earth as it ages and what does this mean for life on Earth? Astrobiology The search for life beyond Earth How do we search for life? Reflectance from vegetation Ozone and Oxygen (together) Gases in the atmosphere produced by living things Ammonia Liquid water Methane How do we find these planets? Small dips and little wobbles How do we find these planets? Small dips and little wobbles How do we find the biosignatures? Need a new generation of space telescopes Look at star light passing through a planet's atmosphere Molecules in the atmosphere absorb specific wavelengths of light Why look into Earth's future? Nearly 1000 confirmed planets outside the solar system 12 considered potentially habitable We will eventually find planets that are like the Earth, but much older The habitable lifetime of Earth & Earth-like planets Time (Billions of Years) Hydrogen converted into helium – heavier Changes balance of outward pressure and gravity Results in increasing brightness Increasing luminosity Temperatures on Earth increase... Outgoing radiation Reflection Inc re as ing ... 0 – 0.06 CO2, H2O, ... Back radiation Heat trapping by greenhouse gases Absorbed by surface Re-radiated from surface Incoming Solar Radiation Weathering Higher temperatures More evaporation More clouds More rain Washes out CO2 from the atmosphere via chemical reactions with silicate rocks CO2 is crucial for photosynthesis Less suitable environment for plants Lightning Nitrogen + Oxygen lightning Nitric acid Frequency of lightning strikes increases with increasing temperature Speeds up Oxygen removal from atmosphere Plate tectonics: Supercontinent cycles Supercontinent cycles of 100 million-year time scales Next supercontinent due in ~250 Million years Can lead to expansive, arid interiors Plate tectonics: Cooling core The core is cooling over time Over billion-year time scales this slows plate movement Slows recycling of CO2 from the crust to the atmosphere What does this mean for life on Earth? Fall in CO2 levels leads to harsher conditions for plants 1 Billion Years 280ppm CO2 Removes sources of food and oxygen Results in animal extinctions 1ppm CO2 What does this mean for life on Earth? La rge m am m als to i nv e rte bra t Humans? es The last animals on Earth Animals like termites can digest dead wood and plant matter Riftia – symbiotic worms that live near hydrothermal vents use chemical energy from the vents for food Leaves behind a microbial world Water bears – microscopic animals that can survive a variety of extreme conditions, even exposure to space A future world of microbes Salt Hot springs, Yellowstone High, dry and low oxygen Deep sea vents (hot, high pressure, dark) Runaway ocean evaporation Hydrogen loss from upper atmosphere After average temperatures reach a critical point (55ºC) water vapour enters upper atmosphere Ocean evaporation begins 1 billion years from now Mapping the fate of Earth's final life Mapping the fate of Earth's final life Latitude Mapping the fate of Earth's final life 375 Temperature (°C) 275 “Runaway greenhouse” 175 “Moist greenhouse” 75 Upper temperature limit for life 15 Time from present (Billion years) Conditions no longer suitable for life 1.2 billion years from now at the equator and 1.85 billion years from now at the poles. Following the water to refuges for Earth's last life High altitude pools Temperature decreases with altitude Liquid water could last longer at higher altitudes Life could survive for 400 million years longer than at the surface Following the water to refuges for Earth's last life Could losing the Moon prolong the survival of life? The Moon is receding by 4 cm a year In 1 billion years it will pass a critical distance at which the Earth's obliquity is allowed to vary chaotically Following the water to refuges for Earth's last life Cold-trap caves (ice caves) Less dense, warm air cannot enter Water source Denser, cooler air trapped In winter ICE Heat from surrounding rock Cold trap caves on a planet with a largely varying tilt could support life for nearly 1 billion years longer than at the surface – 2.8 billion years from today. Following the water to refuges for Earth's last life Other refuges: (1) Underground Temperature generally decreases with depth Depends on type of rock, which varies Parts of the crust could remain habitable for much longer than other refuges Following the water to refuges for Earth's last life Other refuges: (2) In the air Microbes are already found in the atmosphere Highest life found at 77 km If life could live and grow in the atmosphere this could be its final refuge How do we detect life on a dying planet? Recently found twin to the Sun 8 billion years old If we found a planet just like Earth, but 3 billion years older, orbiting this star, would we be able to tell if there is any life on this planet? How do we detect life on a dying planet? Number of microbes that can live in a final refuge + Rate at which they produce gases = Flux of gases to the atmosphere + Some atmospheric chemistry = Biosignature gases How do we detect life on a dying planet? How many microbes could live on the farfuture Earth? In soils, subsurface and sea-floor: 8x1029 cells = 800000000000000000000000000000 cells How do we detect life on a dying planet? How many microbes could live on the farfuture Earth? Time from present (Billion years) How do we detect life on a dying planet? How many microbes could live on the farfuture Earth? Those that need oxygen will be low in numbers and disappear faster Best candidates: chemolithotrophs = chemical rock eaters Alto Ribeira State and Tourist Park (PETAR) , São Paulo, Brazil How do we detect life on a dying planet? How many microbes could live on the farfuture Earth? Chemolithotrophs carry out lots of different chemical reactions to make energy Products such as methane, ammonia and carbon dioxide Reach the atmosphere... How do we detect life on a dying planet? How many microbes could live on the farfuture Earth? 1.0 billion years: O2, O3, H2O, C2H6 (ethane), NH3, CH4 2.0 billion years: H2O, CH4 2.8 billion years: CH4 How do we detect life on a dying planet? Back to our dying Earth-like planet... Finding methane may be a sign on life, but we may need other clues How do we detect life on a dying planet? New biosignatures? There may be other fingerprints of life on a dying planet, e.g. clouds...More science to be done! The Time-line of Earth's future 1.0 billion years Brightening Sun raises temperatures CO2 loss Extinction of plants and animals Runaway greenhouse Microbes inherit the Earth Ocean loss 2.8 billion years Planet gradually sterilised Not necessarily the end of life in the solar system... Saturn's moon Titan is full of cold, organic material Heating this up could give rise to a new origin of life