Paleoatmospheric Chemistry

地球早期大气层的组成 使用一维光化学模型进行研究。 三 将讨论具体问题。 第一个问题是， 撞击可能会将二氧化碳占主导地位的大气层转变为 在最初的几亿年里， 地球的历史。 大气的氧化状态， 尤其是碳氧比是一个重要的界限 生命起源的条件。 第二个问题涉及 与氨，甲烷和硫之间的耦合， 早期的氛围 元素硫蒸气可能提供了 一个有效的屏障，防止太阳近紫外线辐射，如果 早期的地球比现在温暖。 通过屏蔽氨和 甲烷的光解，这样的屏幕可能已经允许了很多 更高浓度的这些气体存在于 气氛 这也可能影响到生命的起源。 第三个问题涉及从减少 氧化气氛中。 光化学模型将是 用于模拟含有低水平O2的大气（约 10-10至10-5倍存在），并确定氧气 浓度会稳定下来，一旦光合作用 使还原气体的供应不堪重负。

The composition of the earth's early atmospheric will be studied using a one-dimensional photochemical model. Three specific questions will be addressed. The first is whether impacts could have converted a CO2-dominated atmosphere into a CO-dominated one during the first several hundred million years of the earth's history. The oxidation state of the atmosphere, and the C/O ratio in particular, is an important boundary condition on the origin of life. The second question deals with the coupling between ammonia, methane, and sulfur in the early atmosphere. Elemental sulfur vapor could have provided an effective screen against solar near-UV radiation if the early earth was warmer than today. By shielding ammonia and methane from photolysis, such a screen may have allowed much higher concentrations of these gases to exist in the prebiotic atmosphere. This, too, could have affected the origin of life. The third question concerns the transition from a reducing to an oxidizing atmosphere. The photochemical model will be used to simulate atmospheres containing low levels of O2 (about 10-10 to 10-5 times present) and to determine where the oxygen concentration would have stabilized once photosynthesis had overwhelmed the supply of reduced gases.