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mm你的版本里面好像没有以下jj，我补充一下。但是请原作者原谅我没有记下出处。 1，Pesticide 植物有自身基因抗病性, 所以建议不要喷农药.有一点记得很清楚, 改造黄瓜可以使其抗12种病毒,但有一种病毒不包括,.基因抗药性可能对植物自身不好, 阻止生长. 很长.. 3或4段 2，Vaccine 一种vaccine 应用于 wild animal 不是很有效，
最近的 research 如何改进了这种vaccine。 3， Great Extinction 第一段 由于地球遭到撞击，造成了物种的灭绝。下面举了化石等几个方面的例子证明这种观点有道理。 第二段 但有些物种是逐渐灭绝的，所以不是撞击造成的，所以还有其它原因。 第三段 火山爆发造成全球变暖，水里面的氧气少了，会产生一种细菌，这种细菌对很多生物有毒，可能造成它们的灭绝。 4，相对平级制关于在公司里是否应该采用相对平级制，也就是员工有机会参与到decision making and buying stock shares of the company等等，其中谈到好处是increase work efficiency, changes in attutide等等，但是经理对于这种体制持保留态度，怕被夺权，也谈到labor unions对这种体制的态度，担心如果公司遭受经济损失，员工的承受能力会很脆弱（因为持有股票），这里是出题点可直接选承受力脆弱那项。 5，Faint young Sun paradox 第一段介绍这个paradox，第二段好像试图carbon oxide解释这个东西，第三段是说有一个科学家提出了一个假设，但是另外一些科学家反驳了这个假设。 记得有个题目是说该文章提供了以下哪条信息，我选择的是有“glacier”的那个……记不大清楚了~ 还有个题目是说文章第一段提***（忘记了，不好意思）有什么用，我选择的是“帮助定义该paradox” 有同学整理了参考资料，严重感谢！当太阳系年轻时，太阳的温度比目前要低25~30%。太阳达到目前的温度大概是在45亿年前。而化石记录显示水和生命在40亿年前就存在。为什么随着太阳温度的上升没有把水烧干？太阳较冷的时候，地球大气中主要是二氧化碳和水。吸收了太阳的部分热量，使地球保持温暖。没有二氧化碳的月亮的地表平均温度是-18C，地球是15C，仅仅因为地球大所中0.035%的二氧化碳及水气、甲烷等有温室效应的气体（硝酸、氧不吸收热量）。 The faint young sun paradox describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the sun's output would be only 70% as intense during that epoch as it is during the modern epoch.
The standard solar model describes the history and evolution of stars. An aspect of this model is that stars similar to the sun should gradually brighten over their life time (excluding a very bright phase just after formation). This prediction is supported by the observation of lower brightness in young stars of solar type. However, with the predicted brightness 4 billion (109) years ago and with greenhouse gas concentrations the same as are current for the modern Earth, any liquid water exposed to the surface would quickly freeze solid. This contradicts geological observations of sedimentary rocks, which required the presence of flowing liquid water to form. The tension between the two hypotheses stems from the incorrect assumption that atmospheric gas concentrations in the past were the same as today. First, before the advent of abundant life the atmospheric oxygen concentrations were orders of magnitude lower than today. In the presence of oxygen methane breaks down to carbon dioxide, so in the absence of oxygen the methane concentration could be much larger than currently observed. Methane is a more potent greenhouse gas than carbon dioxide, so the relative abundance of atmospheric methane throughout Earth's history must be considered when modeling the temperature. Further, the inorganic version of the carbon cycle can be expected to provide negative feedback towards an Earth with liquid water. Carbon dissolved in liquid water can form carbonic acids, which can then interact with calcium to produce calcium carbonate. If rainfall were to cease and the oceans froze over, then this part of the inorganic carbon cycle would shut down. Periodic explosions from volcanoes would then cause a net increase in the atmospheric carbon dioxide and methane levels with no liquid water to absorb these emitted gases. Eventually the concentrations would become large enough that the surface temperature would rise due to the greenhouse effect. When the surface temperature became large enough for the oceans to melt and rainfall to resume the other half of the inorganic carbon cycle would turn on and moderate the greenhouse gas concentrations. It is also noteworthy, that even though evidence of flowing water exists even from very early in Earth's history, there may still have been a number of examples of periods when the Earth's oceans froze over completely. The most recent such period may have been ~630 million years ago, and may have been instrumental in leading the Cambrian explosion of new multicellular life forms. 当太阳系年轻时，太阳的温度比目前要低25~30%。太阳达到目前的温度大概是在45亿年前。而化石记录显示水和生命在40亿年前就存在。为什么随着太阳温度的上升没有把水烧干？太阳较冷的时候，地球大气中主要是二氧化碳和水。吸收了太阳的部分热量，使地球保持温暖。没有二氧化碳的月亮的地表平均温度是-18C，地球是15C，仅仅因为地球大所中0.035%的二氧化碳及水气、甲烷等有温室效应的气体（硝酸、氧不吸收热量）。 The faint young sun paradox describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the sun's output would be only 70% as intense during that epoch as it is during the modern epoch.
The standard solar model describes the history and evolution of stars. An aspect of this model is that stars similar to the sun should gradually brighten over their life time (excluding a very bright phase just after formation). This prediction is supported by the observation of lower brightness in young stars of solar type. However, with the predicted brightness 4 billion (109) years ago and with greenhouse gas concentrations the same as are current for the modern Earth, any liquid water exposed to the surface would quickly freeze solid. This contradicts geological observations of sedimentary rocks, which required the presence of flowing liquid water to form. The tension between the two hypotheses stems from the incorrect assumption that atmospheric gas concentrations in the past were the same as today. First, before the advent of abundant life the atmospheric oxygen concentrations were orders of magnitude lower than today. In the presence of oxygen methane breaks down to carbon dioxide, so in the absence of oxygen the methane concentration could be much larger than currently observed. Methane is a more potent greenhouse gas than carbon dioxide, so the relative abundance of atmospheric methane throughout Earth's history must be considered when modeling the temperature. Further, the inorganic version of the carbon cycle can be expected to provide negative feedback towards an Earth with liquid water. Carbon dissolved in liquid water can form carbonic acids, which can then interact with calcium to produce calcium carbonate. If rainfall were to cease and the oceans froze over, then this part of the inorganic carbon cycle would shut down. Periodic explosions from volcanoes would then cause a net increase in the atmospheric carbon dioxide and methane levels with no liquid water to absorb these emitted gases. Eventually the concentrations would become large enough that the surface temperature would rise due to the greenhouse effect. When the surface temperature became large enough for the oceans to melt and rainfall to resume the other half of the inorganic carbon cycle would turn on and moderate the greenhouse gas concentrations. It is also noteworthy, that even though evidence of flowing water exists even from very early in Earth's history, there may still have been a number of examples of periods when the Earth's oceans froze over completely. The most recent such period may have been ~630 million years ago, and may have been instrumental in leading the Cambrian explosion of new multicellular life forms. 关于在公司里是否应该采用相对平级制，也就是员工有机会参与到decision making and buying stock shares of the company等等，其中谈到好处是increase work efficiency, changes in attutide等等，但是经理对于这种体制持保留态度，怕被夺权，也谈到labor unions对这种体制的态度，担心如果公司遭受经济损失，员工的承受能力会很脆弱（因为持有股票），这里是出题点可直接选承受力脆弱那项。 5，Faint young Sun paradox 第一段介绍这个paradox，第二段好像试图carbon oxide解释这个东西，第三段是说有一个科学家提出了一个假设，但是另外一些科学家反驳了这个假设。 记得有个题目是说该文章提供了以下哪条信息，我选择的是有“glacier”的那个……记不大清楚了~ 还有个题目是说文章第一段提***（忘记了，不好意思）有什么用，我选择的是“帮助定义该paradox” 有同学整理了参考资料，严重感谢！当太阳系年轻时，太阳的温度比目前要低25~30%。太阳达到目前的温度大概是在45亿年前。而化石记录显示水和生命在40亿年前就存在。为什么随着太阳温度的上升没有把水烧干？太阳较冷的时候，地球大气中主要是二氧化碳和水。吸收了太阳的部分热量，使地球保持温暖。没有二氧化碳的月亮的地表平均温度是-18C，地球是15C，仅仅因为地球大所中0.035%的二氧化碳及水气、甲烷等有温室效应的气体（硝酸、氧不吸收热量）。 The faint young sun paradox describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the sun's output would be only 70% as intense during that epoch as it is during the modern epoch.
The standard solar model describes the history and evolution of stars. An aspect of this model is that stars similar to the sun should gradually brighten over their life time (excluding a very bright phase just after formation). This prediction is supported by the observation of lower brightness in young stars of solar type. However, with the predicted brightness 4 billion (109) years ago and with greenhouse gas concentrations the same as are current for the modern Earth, any liquid water exposed to the surface would quickly freeze solid. This contradicts geological observations of sedimentary rocks, which required the presence of flowing liquid water to form. The tension between the two hypotheses stems from the incorrect assumption that atmospheric gas concentrations in the past were the same as today. First, before the advent of abundant life the atmospheric oxygen concentrations were orders of magnitude lower than today. In the presence of oxygen methane breaks down to carbon dioxide, so in the absence of oxygen the methane concentration could be much larger than currently observed. Methane is a more potent greenhouse gas than carbon dioxide, so the relative abundance of atmospheric methane throughout Earth's history must be considered when modeling the temperature. Further, the inorganic version of the carbon cycle can be expected to provide negative feedback towards an Earth with liquid water. Carbon dissolved in liquid water can form carbonic acids, which can then interact with calcium to produce calcium carbonate. If rainfall were to cease and the oceans froze over, then this part of the inorganic carbon cycle would shut down. Periodic explosions from volcanoes would then cause a net increase in the atmospheric carbon dioxide and methane levels with no liquid water to absorb these emitted gases. Eventually the concentrations would become large enough that the surface temperature would rise due to the greenhouse effect. When the surface temperature became large enough for the oceans to melt and rainfall to resume the other half of the inorganic carbon cycle would turn on and moderate the greenhouse gas concentrations. It is also noteworthy, that even though evidence of flowing water exists even from very early in Earth's history, there may still have been a number of examples of periods when the Earth's oceans froze over completely. The most recent such period may have been ~630 million years ago, and may have been instrumental in leading the Cambrian explosion of new multicellular life forms. 当太阳系年轻时，太阳的温度比目前要低25~30%。太阳达到目前的温度大概是在45亿年前。而化石记录显示水和生命在40亿年前就存在。为什么随着太阳温度的上升没有把水烧干？太阳较冷的时候，地球大气中主要是二氧化碳和水。吸收了太阳的部分热量，使地球保持温暖。没有二氧化碳的月亮的地表平均温度是-18C，地球是15C，仅仅因为地球大所中0.035%的二氧化碳及水气、甲烷等有温室效应的气体（硝酸、氧不吸收热量）。 The faint young sun paradox describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the sun's output would be only 70% as intense during that epoch as it is during the modern epoch.
The standard solar model describes the history and evolution of stars. An aspect of this model is that stars similar to the sun should gradually brighten over their life time (excluding a very bright phase just after formation). This prediction is supported by the observation of lower brightness in young stars of solar type. However, with the predicted brightness 4 billion (109) years ago and with greenhouse gas concentrations the same as are current for the modern Earth, any liquid water exposed to the surface would quickly freeze solid. This contradicts geological observations of sedimentary rocks, which required the presence of flowing liquid water to form. The tension between the two hypotheses stems from the incorrect assumption that atmospheric gas concentrations in the past were the same as today. First, before the advent of abundant life the atmospheric oxygen concentrations were orders of magnitude lower than today. In the presence of oxygen methane breaks down to carbon dioxide, so in the absence of oxygen the methane concentration could be much larger than currently observed. Methane is a more potent greenhouse gas than carbon dioxide, so the relative abundance of atmospheric methane throughout Earth's history must be considered when modeling the temperature. Further, the inorganic version of the carbon cycle can be expected to provide negative feedback towards an Earth with liquid water. Carbon dissolved in liquid water can form carbonic acids, which can then interact with calcium to produce calcium carbonate. If rainfall were to cease and the oceans froze over, then this part of the inorganic carbon cycle would shut down. Periodic explosions from volcanoes would then cause a net increase in the atmospheric carbon dioxide and methane levels with no liquid water to absorb these emitted gases. Eventually the concentrations would become large enough that the surface temperature would rise due to the greenhouse effect. When the surface temperature became large enough for the oceans to melt and rainfall to resume the other half of the inorganic carbon cycle would turn on and moderate the greenhouse gas concentrations. It is also noteworthy, that even though evidence of flowing water exists even from very early in Earth's history, there may still have been a number of examples of periods when the Earth's oceans froze over completely. The most recent such period may have been ~630 million years ago, and may have been instrumental in leading the Cambrian explosion of new multicellular life forms. 第一段 由于地球遭到撞击，造成了物种的灭绝。下面举了化石等几个方面的例子证明这种观点有道理。 第二段 但有些物种是逐渐灭绝的，所以不是撞击造成的，所以还有其它原因。 第三段 火山爆发造成全球变暖，水里面的氧气少了，会产生一种细菌，这种细菌对很多生物有毒，可能造成它们的灭绝。 4，相对平级制关于在公司里是否应该采用相对平级制，也就是员工有机会参与到decision making and buying stock shares of the company等等，其中谈到好处是increase work efficiency, changes in attutide等等，但是经理对于这种体制持保留态度，怕被夺权，也谈到labor unions对这种体制的态度，担心如果公司遭受经济损失，员工的承受能力会很脆弱（因为持有股票），这里是出题点可直接选承受力脆弱那项。 5，Faint young Sun paradox 第一段介绍这个paradox，第二段好像试图carbon oxide解释这个东西，第三段是说有一个科学家提出了一个假设，但是另外一些科学家反驳了这个假设。 记得有个题目是说该文章提供了以下哪条信息，我选择的是有“glacier”的那个……记不大清楚了~ 还有个题目是说文章第一段提***（忘记了，不好意思）有什么用，我选择的是“帮助定义该paradox” 有同学整理了参考资料，严重感谢！当太阳系年轻时，太阳的温度比目前要低25~30%。太阳达到目前的温度大概是在45亿年前。而化石记录显示水和生命在40亿年前就存在。为什么随着太阳温度的上升没有把水烧干？太阳较冷的时候，地球大气中主要是二氧化碳和水。吸收了太阳的部分热量，使地球保持温暖。没有二氧化碳的月亮的地表平均温度是-18C，地球是15C，仅仅因为地球大所中0.035%的二氧化碳及水气、甲烷等有温室效应的气体（硝酸、氧不吸收热量）。 The faint young sun paradox describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the sun's output would be only 70% as intense during that epoch as it is during the modern epoch.
The standard solar model describes the history and evolution of stars. An aspect of this model is that stars similar to the sun should gradually brighten over their life time (excluding a very bright phase just after formation). This prediction is supported by the observation of lower brightness in young stars of solar type. However, with the predicted brightness 4 billion (109) years ago and with greenhouse gas concentrations the same as are current for the modern Earth, any liquid water exposed to the surface would quickly freeze solid. This contradicts geological observations of sedimentary rocks, which required the presence of flowing liquid water to form. The tension between the two hypotheses stems from the incorrect assumption that atmospheric gas concentrations in the past were the same as today. First, before the advent of abundant life the atmospheric oxygen concentrations were orders of magnitude lower than today. In the presence of oxygen methane breaks down to carbon dioxide, so in the absence of oxygen the methane concentration could be much larger than currently observed. Methane is a more potent greenhouse gas than carbon dioxide, so the relative abundance of atmospheric methane throughout Earth's history must be considered when modeling the temperature. Further, the inorganic version of the carbon cycle can be expected to provide negative feedback towards an Earth with liquid water. Carbon dissolved in liquid water can form carbonic acids, which can then interact with calcium to produce calcium carbonate. If rainfall were to cease and the oceans froze over, then this part of the inorganic carbon cycle would shut down. Periodic explosions from volcanoes would then cause a net increase in the atmospheric carbon dioxide and methane levels with no liquid water to absorb these emitted gases. Eventually the concentrations would become large enough that the surface temperature would rise due to the greenhouse effect. When the surface temperature became large enough for the oceans to melt and rainfall to resume the other half of the inorganic carbon cycle would turn on and moderate the greenhouse gas concentrations. It is also noteworthy, that even though evidence of flowing water exists even from very early in Earth's history, there may still have been a number of examples of periods when the Earth's oceans froze over completely. The most recent such period may have been ~630 million years ago, and may have been instrumental in leading the Cambrian explosion of new multicellular life forms. 当太阳系年轻时，太阳的温度比目前要低25~30%。太阳达到目前的温度大概是在45亿年前。而化石记录显示水和生命在40亿年前就存在。为什么随着太阳温度的上升没有把水烧干？太阳较冷的时候，地球大气中主要是二氧化碳和水。吸收了太阳的部分热量，使地球保持温暖。没有二氧化碳的月亮的地表平均温度是-18C，地球是15C，仅仅因为地球大所中0.035%的二氧化碳及水气、甲烷等有温室效应的气体（硝酸、氧不吸收热量）。 The faint young sun paradox describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the sun's output would be only 70% as intense during that epoch as it is during the modern epoch.
The standard solar model describes the history and evolution of stars. An aspect of this model is that stars similar to the sun should gradually brighten over their life time (excluding a very bright phase just after formation). This prediction is supported by the observation of lower brightness in young stars of solar type. However, with the predicted brightness 4 billion (109) years ago and with greenhouse gas concentrations the same as are current for the modern Earth, any liquid water exposed to the surface would quickly freeze solid. This contradicts geological observations of sedimentary rocks, which required the presence of flowing liquid water to form. The tension between the two hypotheses stems from the incorrect assumption that atmospheric gas concentrations in the past were the same as today. First, before the advent of abundant life the atmospheric oxygen concentrations were orders of magnitude lower than today. In the presence of oxygen methane breaks down to carbon dioxide, so in the absence of oxygen the methane concentration could be much larger than currently observed. Methane is a more potent greenhouse gas than carbon dioxide, so the relative abundance of atmospheric methane throughout Earth's history must be considered when modeling the temperature. Further, the inorganic version of the carbon cycle can be expected to provide negative feedback towards an Earth with liquid water. Carbon dissolved in liquid water can form carbonic acids, which can then interact with calcium to produce calcium carbonate. If rainfall were to cease and the oceans froze over, then this part of the inorganic carbon cycle would shut down. Periodic explosions from volcanoes would then cause a net increase in the atmospheric carbon dioxide and methane levels with no liquid water to absorb these emitted gases. Eventually the concentrations would become large enough that the surface temperature would rise due to the greenhouse effect. When the surface temperature became large enough for the oceans to melt and rainfall to resume the other half of the inorganic carbon cycle would turn on and moderate the greenhouse gas concentrations. It is also noteworthy, that even though evidence of flowing water exists even from very early in Earth's history, there may still have been a number of examples of periods when the Earth's oceans froze over completely. The most recent such period may have been ~630 million years ago, and may have been instrumental in leading the Cambrian explosion of new multicellular life forms. 关于在公司里是否应该采用相对平级制，也就是员工有机会参与到decision making and buying stock shares of the company等等，其中谈到好处是increase work efficiency, changes in attutide等等，但是经理对于这种体制持保留态度，怕被夺权，也谈到labor unions对这种体制的态度，担心如果公司遭受经济损失，员工的承受能力会很脆弱（因为持有股票），这里是出题点可直接选承受力脆弱那项。 5，Faint young Sun paradox 第一段介绍这个paradox，第二段好像试图carbon oxide解释这个东西，第三段是说有一个科学家提出了一个假设，但是另外一些科学家反驳了这个假设。 记得有个题目是说该文章提供了以下哪条信息，我选择的是有“glacier”的那个……记不大清楚了~ 还有个题目是说文章第一段提***（忘记了，不好意思）有什么用，我选择的是“帮助定义该paradox” 有同学整理了参考资料，严重感谢！当太阳系年轻时，太阳的温度比目前要低25~30%。太阳达到目前的温度大概是在45亿年前。而化石记录显示水和生命在40亿年前就存在。为什么随着太阳温度的上升没有把水烧干？太阳较冷的时候，地球大气中主要是二氧化碳和水。吸收了太阳的部分热量，使地球保持温暖。没有二氧化碳的月亮的地表平均温度是-18C，地球是15C，仅仅因为地球大所中0.035%的二氧化碳及水气、甲烷等有温室效应的气体（硝酸、氧不吸收热量）。 The faint young sun paradox describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the sun's output would be only 70% as intense during that epoch as it is during the modern epoch.
The standard solar model describes the history and evolution of stars. An aspect of this model is that stars similar to the sun should gradually brighten over their life time (excluding a very bright phase just after formation). This prediction is supported by the observation of lower brightness in young stars of solar type. However, with the predicted brightness 4 billion (109) years ago and with greenhouse gas concentrations the same as are current for the modern Earth, any liquid water exposed to the surface would quickly freeze solid. This contradicts geological observations of sedimentary rocks, which required the presence of flowing liquid water to form. The tension between the two hypotheses stems from the incorrect assumption that atmospheric gas concentrations in the past were the same as today. First, before the advent of abundant life the atmospheric oxygen concentrations were orders of magnitude lower than today. In the presence of oxygen methane breaks down to carbon dioxide, so in the absence of oxygen the methane concentration could be much larger than currently observed. Methane is a more potent greenhouse gas than carbon dioxide, so the relative abundance of atmospheric methane throughout Earth's history must be considered when modeling the temperature. Further, the inorganic version of the carbon cycle can be expected to provide negative feedback towards an Earth with liquid water. Carbon dissolved in liquid water can form carbonic acids, which can then interact with calcium to produce calcium carbonate. If rainfall were to cease and the oceans froze over, then this part of the inorganic carbon cycle would shut down. Periodic explosions from volcanoes would then cause a net increase in the atmospheric carbon dioxide and methane levels with no liquid water to absorb these emitted gases. Eventually the concentrations would become large enough that the surface temperature would rise due to the greenhouse effect. When the surface temperature became large enough for the oceans to melt and rainfall to resume the other half of the inorganic carbon cycle would turn on and moderate the greenhouse gas concentrations. It is also noteworthy, that even though evidence of flowing water exists even from very early in Earth's history, there may still have been a number of examples of periods when the Earth's oceans froze over completely. The most recent such period may have been ~630 million years ago, and may have been instrumental in leading the Cambrian explosion of new multicellular life forms. 当太阳系年轻时，太阳的温度比目前要低25~30%。太阳达到目前的温度大概是在45亿年前。而化石记录显示水和生命在40亿年前就存在。为什么随着太阳温度的上升没有把水烧干？太阳较冷的时候，地球大气中主要是二氧化碳和水。吸收了太阳的部分热量，使地球保持温暖。没有二氧化碳的月亮的地表平均温度是-18C，地球是15C，仅仅因为地球大所中0.035%的二氧化碳及水气、甲烷等有温室效应的气体（硝酸、氧不吸收热量）。 The faint young sun paradox describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the sun's output would be only 70% as intense during that epoch as it is during the modern epoch.
The standard solar model describes the history and evolution of stars. An aspect of this model is that stars similar to the sun should gradually brighten over their life time (excluding a very bright phase just after formation). This prediction is supported by the observation of lower brightness in young stars of solar type. However, with the predicted brightness 4 billion (109) years ago and with greenhouse gas concentrations the same as are current for the modern Earth, any liquid water exposed to the surface would quickly freeze solid. This contradicts geological observations of sedimentary rocks, which required the presence of flowing liquid water to form. The tension between the two hypotheses stems from the incorrect assumption that atmospheric gas concentrations in the past were the same as today. First, before the advent of abundant life the atmospheric oxygen concentrations were orders of magnitude lower than today. In the presence of oxygen methane breaks down to carbon dioxide, so in the absence of oxygen the methane concentration could be much larger than currently observed. Methane is a more potent greenhouse gas than carbon dioxide, so the relative abundance of atmospheric methane throughout Earth's history must be considered when modeling the temperature. Further, the inorganic version of the carbon cycle can be expected to provide negative feedback towards an Earth with liquid water. Carbon dissolved in liquid water can form carbonic acids, which can then interact with calcium to produce calcium carbonate. If rainfall were to cease and the oceans froze over, then this part of the inorganic carbon cycle would shut down. Periodic explosions from volcanoes would then cause a net increase in the atmospheric carbon dioxide and methane levels with no liquid water to absorb these emitted gases. Eventually the concentrations would become large enough that the surface temperature would rise due to the greenhouse effect. When the surface temperature became large enough for the oceans to melt and rainfall to resume the other half of the inorganic carbon cycle would turn on and moderate the greenhouse gas concentrations. It is also noteworthy, that even though evidence of flowing water exists even from very early in Earth's history, there may still have been a number of examples of periods when the Earth's oceans froze over completely. The most recent such period may have been ~630 million years ago, and may have been instrumental in leading the Cambrian explosion of new multicellular life forms.
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