< p >你是正确的思想,氧气来自光合作用。事实上它是与光合作用有关,而不是任何无机过程中,氧气的存在在其他行星的大气光谱(太阳能或系外行星)被认为是地外生命的最佳指标之一——没有这样发现了氧气。臭氧是由预先存在的氧气,但只有12分钟的大气半衰期,自发地再次变回氧气非常迅速,并且对ozone-disrupting代理氯氟烃等高度敏感。陨石几乎没有,如果任何自由氧。事实上,许多陨石含有Ni-Fe会迅速吸收任何自由氧如果它最初是礼物。火山活动反映了岩浆房的逃亡的气体,其中包含F, Cl,二氧化碳,有限公司,H2O,硫化氢,N2,惰性气体,氢气。氧气可以发生在几个火山的排泄物感到但这是罕见的,规模小。总的来说,火山是氧气吸收而不是排放国。Photo-dissociation发生某种程度上高我们的大气层对太阳和宇宙辐射。结果是水= H + +哦,所以没有免费的氧气。 In any case, the two ions recombine fairly rapidly. Photo-dissociation is important in dense interstellar gas clouds far out in space where they may be subject to intense UV-radiation. Even here, the tendency is to mop up rather than release free oxygen. The photosynthetic activity and mechanism on Earth has changed dramatically. It is the only known mechanism which can and does release large quantities of free oxygen. This started more than 3 billion years ago, but didn't raise the atmospheric oxygen level significantly prior to about 2.5 billion years ago. Evolution of the Earth's oxygen has been a long and complex affair, with high levels of oxygen only starting to emerge in the Eocambrian. The Earth's first oxygen would have been a noxious, toxic, and horribly reactive gas from the perspective of the Earth's earliest unicellular organisms. New information just in: Nature magazine, 28th October 2015, has reported an astonishingly high oxygen concentration, of 3.8%, from the gaseous emissions from comet 67P, as measured by the Rosetta space probe. This has taken everyone by surprise (including myself) and may require a re-think about comet formation.