Generation of Oxygen Before Life
Recent study has shown that oxygen can be formed directly from carbon dioxide in the upper atmosphere, changing the prior models of how the atmosphere evolved early in Earth’s history.
About one fifth of the Earth’s atmosphere is oxygen. This oxygen is produced by green vegetation as a result of photosynthesis and used by most living beings on the planet to keep our metabolisms running. But before the first photosynthesizing organisms appeared, which is about 2.4 billion years ago, the atmosphere possibly contained mostly carbon dioxide, as is the case today on Mars and Venus.
Over the last 40 years, researchers had an idea of having a small amount of oxygen in the primitive atmosphere. But origin of this first abiotic (no green plants involved) oxygen was not clear. Oxygen reacts rather aggressively with other compounds, so it would not persist for long, once produced, without some incessant source.
A novel recent study, conducted in the Departments of Chemistry and of Earth and Planetary Sciences, has shown that oxygen can be formed in one step by using a high energy vacuum ultraviolet laser to excite carbon dioxide.
The work is published in the journal, Science elaborates that, people used to think that abiotic source of molecular oxygen is by CO2 + solar light –> CO + O and O + O + M –> O2 + M (where M represents a third body carrying off the energy released in forming the oxygen bond). However the new study indicates that O2 can be formed by carbon dioxide dissociation in a one step process. The same process can be applied in other carbon dioxide dominated atmospheres such as Mars and Venus. The researchers used a vacuum ultraviolet laser to irradiate CO2 in the laboratory. Vacuum ultraviolet light is so-called because it has a wavelength below 200 nano-meters and is typically absorbed by air. The experiments were performed by using a unique ion imaging apparatus developed at UC Davis.
This type of one-step oxygen formation could be happening in current weather conditions as carbon dioxide increases in the region of the upper atmosphere, where high energy vacuum ultraviolet light from the Sun hits Earth or other planets. This is the first attempt to show such a reaction in the laboratory. According to one of the scientists who reviewed the paper for Science, this work means that models of the evolution of planetary atmospheres will now have to be adjusted considering this model.
Z. Lu, Y. C. Chang, Q.-Z. Yin, C. Y. Ng, W. M. Jackson. Evidence for direct molecular oxygen production in CO2 photodissociation. Science, 2014; 346 (6205): 61 DOI: 10.1126/science.1257156
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