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CHAPTER 21 The Chemistry of the Solar System 21.3 The Possibility of Life Elsewhere Life on Earth What does life look like? A tadpole Soil bacteria ‹#› Humans and plants 21.3 The Possibility of Life Elsewhere Searching for life beyond Earth Key questions before searching for extraterrestrial life: - What are the physical and chemical conditions under which life can exist? - Do those conditions exist outside of Earth? If so, where? - How would we recognize alien life if we found it? ‹#› 21.3 The Possibility of Life Elsewhere Chemosynthetic life In the deep ocean, at very high pressure and in absolute darkness, hydrothermal vents release acidic, superheated water that contains heavy metals. ‹#› 21.3 The Possibility of Life Elsewhere Chemosynthetic life In the deep ocean, at very high pressure and in absolute darkness, hydrothermal vents release acidic, superheated water that contains heavy metals. Still chemosynthetic life exists at hydrothermal vents! ‹#› 21.3 The Possibility of Life Elsewhere Life deep underground Only recently, scientists discovered living colonies of bacteria 2.8 km underground with no organic materials around. Deep bacteria like Bacillus infernus are considered thermophiles (heat lovers) because they thrive at 75oC (167oF). ‹#› 21.3 The Possibility of Life Elsewhere Evidence for life on Mars Four experiments: 1) A mass spectrometer looked for organic compounds. 2) A gas exchange experiment looked for O2, CO2, H2, CH4 and N2. 3) A labeled release experiment involved a 14C-labeled nutrient solution. 4) A pyrolytic release experiment used light and 14CO2. The results from Viking were inconclusive because samples were small, and the instruments were not as sophisticated as they are today. ‹#› 21.3 The Possibility of Life Elsewhere Evidence for life on Mars In 2008, the Phoenix mission landed on Mars and found: 1) water in the form of ice 2) salts and perchlorate (ClO4). Perchlorate is not a signature of life, but some microorganisms on Earth are fueled by processes that involve perchlorate. ‹#› 21.3 The Possibility of Life Elsewhere Life on Europa? Europa is Jupiter’s sixth moon ‹#› 21.3 The Possibility of Life Elsewhere Life on Europa? In 1997 the Galileo spacecraft showed that the surface of Europa is criss-crossed with strange lines, and there are almost no craters. Why do many scientists believe that Europa is a likely candidate for extraterrestrial life? Europa’s surface from 200 km altitude ‹#› 21.3 The Possibility of Life Elsewhere Life on Europa? Ice crust Water ocean Scientists believe that the surface is made of water ice, which hides water oceans that are 200 km deep! The deepest oceans on Earth are less than 10 km deep. It is believed that the water remains liquid because of Rock mantle ‹#› Iron-rich core Jupiter’s gravity causing strong tides and frictional heating. 21.3 The Possibility of Life Elsewhere Life on Titan? In 2005, the Cassini-Huyens spacecraft showed that Titan is like a planet, with oceans, rivers, mountains, and even weather! Titan is Saturn’s sixth moon. ‹#› 21.3 The Possibility of Life Elsewhere Life on Titan? In 2005, the Cassini-Huyens spacecraft showed that Titan is like a planet, with oceans, rivers, mountains, and even weather! Titan offers abundant organic liquids and a dense nitrogen atmosphere. Scientists believe that, except for the cold (–180oC), these conditions are similar to the early Earth. If Titan has underground caves that are warmer, the chances of finding life will be much greater. ‹#› 21.3 The Possibility of Life Elsewhere Life on Earth can exist under extreme conditions: high temperature, high pressure, without light, among toxic chemicals, without organic materials The most likely places to find extraterrestrial life are on: 1) Mars Water (ice) was found, along with salts and perchlorate 2) Europa Vast oceans are believed to exist below the crust of ice 3) Titan This moon has a diverse landscape and even weather. Organic materials were found in abundance and, except for the extreme cold, the conditions are similar to what the early Earth might have been. ‹#› 21.3 The Possibility of Life Elsewhere