oxygen in earth atmosphere comes from ultraviolet radiation.
oxygen in earth atmosphere comes from ultraviolet radiation.
where does oxygen in earth atmosphere come from?
ultraviolet radiation
before photosynthesis evolved, earth's atmosphere had no free oxygen (o). photosynthetic prokaryotic organisms that produced o as a waste product lived long before the first build-up of free oxygen in the atmosphere, perhaps as early as 3.5 billion years ago. the oxygen they produced would have been rapidly removed from the atmosphere by weathering of reducing minerals, most notably iron. this "mass rusting" led to the deposition of iron oxide on the ocean floor, forming banded iron formations. oxygen only began to persist in the atmosphere in small quantities about 50 million years before the start of the great oxygenation event. this mass oxygenation of the atmosphere resulted in rapid buildup of free oxygen. at current rates of primary production, today's concentration of oxygen could be produced by photosynthetic organisms in 2,000 years. in the absence of plants, the rate of oxygen production by photosynthesis was slower in the precambrian, and the concentrations of o attained were less than 10% of today's and probably fluctuated greatly; oxygen may even have disappeared from the atmosphere again around 1.9 billion years ago. these fluctuations in oxygen concentration had little direct effect on life, with mass extinctions not observed until the appearance of complex life around the start of the cambrian period, . the presence of provided life with new opportunities. aerobic metabolism is more efficient than anaerobic pathways, and the presence of oxygen created new possibilities for life to explore. since the start of the cambrian period, atmospheric oxygen concentrations have fluctuated between 15% and 35% of atmospheric volume. the maximum of 35% was reached towards the end of the carboniferous period (about 300 million years ago), a peak which may have contributed to the large size of insects and amphibians at that time. whilst human activities, such as the burning of fossil fuels, affect relative carbon dioxide concentrations, their effect on the much larger concentration of oxygen is less significant.
geological history of oxygen
the hydroxyl oh radical is one of the main chemical species controlling the oxidizing capacity of the global earth atmosphere. this oxidizing reactive species has a major impact on the concentrations and distribution of greenhouse gases and pollutants in the earth atmosphere. it is the most widespread oxidizer in the troposphere, the lowest part of the atmosphere. understanding oh variability is important to evaluating human impacts on the atmosphere and climate. the oh species has a lifetime in the earth atmosphere of less than one second. understanding the role of oh in the oxidation process of methane (ch) present in the atmosphere to first carbon monoxide (co) and then carbon dioxide (co) is important for assessing the residence time of this greenhouse gas, the overall carbon budget of the troposphere, and its influence on the process of global warming. the lifetime of oh radicals in the earth atmosphere is very short, therefore oh concentrations in the air are very low and very sensitive techniques are required for its direct detection. global average hydroxyl radical concentrations have been measured indirectly by analyzing methyl chloroform (chccl) present in the air. the results obtained by montzka "et al." (2011) shows that the interannual variability in oh estimated from chccl measurements is small, indicating that global oh is generally well buffered against perturbations. this small variability is consistent with measurements of methane and other trace gases primarily oxidized by oh, as well as global photochemical model calculations.
hydroxyl radical