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托福阅读真题第34篇Water and Life on Mars Water and Life on Mars The question of life on Mars depends heavily on the characteristics of its air and water. Mars has a relatively thin and dry atmosphere, with high percentage of carbon dioxide compared to Earth's atmosphere. Mars tilts about25°,which leads to seasons like those on Earth. Carbon dioxide freezes into the polar caps during the winter and evaporates into the air in the summer This causes a fluctuation in the density of the atmosphere of up to 25 percent over the year With so little atmosphere, the planet experiences a wide range of temperatures, heating up in the day and rapidly cooling at night. Temperatures on Mars have been measured between-225F and95° Scientists remain fascinated by the possibility of liquid water on Mars. Life as we know it requires water so it should be good marker for habitability. Current conditions on Mars suggest that liquid water could not occur on the surface. The low pressure and low temperature mean that ice would sublime-go straight from solid to gas-rather than melt. Water may be hiding in subsurface reservoirs, however, and stream forth for limited periods. In 2002 the Mars Odyssey orbiter detected large quantities of water ice near the surface of the southern hemisphere Channels on the surface suggest the presence of moving water in large quantities. In 2006 Mars Global Surveyor provided pictures of gullies (channels) on the surface that could only have been produced by liquid water flowing within the past seven years. Theories exist for how climate and erosion may reveal underground ice and cause sudden floods, but specific details are still a mystery. The water probably represents flash floods that quickly evaporate and may not provide an adequate medium for the development of life. If life arose in the distant past, though, the selfish floods may have been enough to maintain organisms adapted to such environments. Astrobiologists continue to investigate whether the current situation-frozen water with occasional flash floods-was always the situation on Mars. Some surface channels on Mars could not have been produced by flash floods or geologic activity.The Opportunity rover, which landed on Mars in 2004. made two interesting discoveries in several craters on Mars. Rock layers on the sides of the craters look like the patterns inside sedimentary rocks on Earth. Sedimentary rocks form gradually at the bottom of bodies of water as particles settle down to the bottom. Sedimentary rocks on Mars would imply that a bod y of water was present for hundreds of years at some point in the past. In addition, Opportunity has found countless tiny spheres of the mineral hematite (a mineral composed of iron and oxygen) on the surface. These tiny spheres, or "blueberries" as they have come to be called, strongly resemble accretions ( accumulations) found on Earth in highly acidic stream beds. Together with rippling patterns in the stone of the surface, the layers and blueberries make a compelling argument. Acidic, salty, flowing water must once have covered large regions of the plain where Opportunity landed. The Sun has been very slowly cooling off the past few billions of years. A warmer Sun in the past means a warmer Mars. Planetary scientists do not think the difference was enough to bring Mars up to Earth like temperatures, but it may have been enough to support liquid water in the warmer regions of the planet. Overall, Mars looks like a good candidate for past life. Water, carbon, and energy were all present in useful amounts. If life arises quickly wherever resources allow, then Mars probably had life once. Unfortunately we have no way to assess how common the origin of life might be. This is one of the questions scientists were asking when they explored Mars in the first place. Astrobiologists Another import ant question to ask in the exploration of Mars has to disagree about evidence for life in the first billion years of Earth's history. Mars' history must be even more contentious. The most unambiguous evidence of life on Earth comes in the form of structural fossils, which probably did not start forming on Earth until life had been around for at least a billion years. If life did arise on Mars, it may not have been around long enough to leave that kind of evidence. 1.The question of life on Mars depends heavily on the characteristics of its air and water. Mars has a relatively thin and dry atmosphere, with high percentage of carbon dioxide compared to Earth's atmosphere. Mars tilts about25°,which leads to seasons like those on Earth. Carbon dioxide freezes into the polar caps during the winter and evaporates into the air in the summer This causes a fluctuation in the density of the atmosphere of up to 25 percent over the year With so little atmosphere, the planet experiences a wide range of temperatures, heating up in the day and rapidly cooling at night. Temperatures on Mars have been measured between-225F and95° 2.Scientists remain fascinated by the possibility of liquid water on Mars. Life as we know it requires water so it should be good marker for habitability. Current conditions on Mars suggest that liquid water could not occur on the surface. The low pressure and low temperature mean that ice would sublime-go straight from solid to gas-rather than melt. Water may be hiding in subsurface reservoirs, however, and stream forth for limited periods. In 2002 the Mars Odyssey orbiter detected large quantities of water ice near the surface of the southern hemisphere Channels on the surface suggest the presence of moving water in large quantities. In 2006 Mars Global Surveyor provided pictures of gullies (channels) on the surface that could only have been produced by liquid water flowing within the past seven years. Theories exist for how climate and erosion may reveal underground ice and cause sudden floods, but specific details are still a mystery. The water probably represents flash floods that quickly evaporate and may not provide an adequate medium for the development of life. If life arose in the distant past, though, the selfish floods may have been enough to maintain organisms adapted to such environments. 3.Scientists remain fascinated by the possibility of liquid water on Mars. Life as we know it requires water so it should be good marker for habitability. Current conditions on Mars suggest that liquid water could not occur on the surface. The low pressure and low temperature mean that ice would sublime-go straight from solid to gas-rather than melt. Water may be hiding in subsurface reservoirs, however, and stream forth for limited periods. In 2002 the Mars Odyssey orbiter detected large quantities of water ice near the surface of the southern hemisphere Channels on the surface suggest the presence of moving water in large quantities. In 2006 Mars Global Surveyor provided pictures of gullies (channels) on the surface that could only have been produced by liquid water flowing within the past seven years. Theories exist for how climate and erosion may reveal underground ice and cause sudden floods, but specific details are still a mystery. The water probably represents flash floods that quickly evaporate and may not provide an adequate medium for the development of life. If life arose in the distant past, though, the selfish floods may have been enough to maintain organisms adapted to such environments. 4.Astrobiologists continue to investigate whether the current situation-frozen water with occasional flash floods-was always the situation on Mars. Some surface channels on Mars could not have been produced by flash floods or geologic activity.The Opportunity rover, which landed on Mars in 2004. made two interesting discoveries in several craters on Mars. Rock layers on the sides of the craters look like the patterns inside sedimentary rocks on Earth. Sedimentary rocks form gradually at the bottom of bodies of water as particles settle down to the bottom. Sedimentary rocks on Mars would imply that a bod y of water was present for hundreds of years at some point in the past. In addition, Opportunity has found countless tiny spheres of the mineral hematite (a mineral composed of iron and oxygen) on the surface. These tiny spheres, or "blueberries" as they have come to be called, strongly resemble accretions ( accumulations) found on Earth in highly acidic stream beds. Together with rippling patterns in the stone of the surface, the layers and blueberries make a compelling argument. Acidic, salty, flowing water must once have covered large regions of the plain where Opportunity landed. The Sun has been very slowly cooling off the past few billions of years. A warmer Sun in the past means a warmer Mars. Planetary scientists do not think the difference was enough to bring Mars up to Earth like temperatures, but it may have been enough to support liquid water in the warmer regions of the planet. 5.Astrobiologists continue to investigate whether the current situation-frozen water with occasional flash floods-was always the situation on Mars. Some surface channels on Mars could not have been produced by flash floods or geologic activity.The Opportunity rover, which landed on Mars in 2004. made two interesting discoveries in several craters on Mars. Rock layers on the sides of the craters look like the patterns inside sedimentary rocks on Earth. Sedimentary rocks form gradually at the bottom of bodies of water as particles settle down to the bottom. Sedimentary rocks on Mars would imply that a bod y of water was present for hundreds of years at some point in the past. In addition, Opportunity has found countless tiny spheres of the mineral hematite (a mineral composed of iron and oxygen) on the surface. These tiny spheres, or "blueberries" as they have come to be called, strongly resemble accretions ( accumulations) found on Earth in highly acidic stream beds. Together with rippling patterns in the stone of the surface, the layers and blueberries make a compelling argument. Acidic, salty, flowing water must once have covered large regions of the plain where Opportunity landed. The Sun has been very slowly cooling off the past few billions of years. A warmer Sun in the past means a warmer Mars. Planetary scientists do not think the difference was enough to bring Mars up to Earth like temperatures, but it may have been enough to support liquid water in the warmer regions of the planet. 6.Astrobiologists continue to investigate whether the current situation-frozen water with occasional flash floods-was always the situation on Mars. Some surface channels on Mars could not have been produced by flash floods or geologic activity.The Opportunity rover, which landed on Mars in 2004. made two interesting discoveries in several craters on Mars. Rock layers on the sides of the craters look like the patterns inside sedimentary rocks on Earth. Sedimentary rocks form gradually at the bottom of bodies of water as particles settle down to the bottom. Sedimentary rocks on Mars would imply that a bod y of water was present for hundreds of years at some point in the past. In addition, Opportunity has found countless tiny spheres of the mineral hematite (a mineral composed of iron and oxygen) on the surface. These tiny spheres, or "blueberries" as they have come to be called, strongly resemble accretions ( accumulations) found on Earth in highly acidic stream beds. Together with rippling patterns in the stone of the surface, the layers and blueberries make a compelling argument. Acidic, salty, flowing water must once have covered large regions of the plain where Opportunity landed. The Sun has been very slowly cooling off the past few billions of years. A warmer Sun in the past means a warmer Mars. Planetary scientists do not think the difference was enough to bring Mars up to Earth like temperatures, but it may have been enough to support liquid water in the warmer regions of the planet. 7.Overall, Mars looks like a good candidate for past life. Water, carbon, and energy were all present in useful amounts. If life arises quickly wherever resources allow, then Mars probably had life once. Unfortunately we have no way to assess how common the origin of life might be. This is one of the questions scientists were asking when they explored Mars in the first place. 8.Astrobiologists Another import ant question to ask in the exploration of Mars has to disagree about evidence for life in the first billion years of Earth's history. Mars' history must be even more contentious. The most unambiguous evidence of life on Earth comes in the form of structural fossils, which probably did not start forming on Earth until life had been around for at least a billion years. If life did arise on Mars, it may not have been around long enough to leave that kind of evidence. 9.Scientists remain fascinated by the possibility of liquid water on Mars. Life as we know it requires water so it should be good marker for habitability. ⬛ Current conditions on Mars suggest that liquid water could not occur on the surface. ⬛ The low pressure and low temperature mean that ice would sublime-go straight from solid to gas-rather than melt. ⬛ Water may be hiding in subsurface reservoirs, however, and stream forth for limited periods. ⬛ In 2002 the Mars Odyssey orbiter detected large quantities of water ice near the surface of the southern hemisphere Channels on the surface suggest the presence of moving water in large quantities. In 2006 Mars Global Surveyor provided pictures of gullies (channels) on the surface that could only have been produced by liquid water flowing within the past seven years. Theories exist for how climate and erosion may reveal underground ice and cause sudden floods, but specific details are still a mystery. The water probably represents flash floods that quickly evaporate and may not provide an adequate medium for the development of life. If life arose in the distant past, though, the selfish floods may have been enough to maintain organisms adapted to such environments. 10. 答案如下： 34篇Water and Life on Mars |
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