According to Oparin, which of the following was not present in the primitive atmosphere of the earth ?
oxygen
Oparin (and independently Haldane) proposed that the early atmosphere was reducing, made up mainly of methane, ammonia, hydrogen and water vapour.
Free molecular oxygen was absent. In a reducing atmosphere organic molecules could form and accumulate, because there was no oxygen to oxidize and break them down; free oxygen appeared much later through oxygenic photosynthesis by cyanobacteria.
Methane, hydrogen and water vapour were all part of the proposed primitive atmosphere, and Miller and Urey later used exactly such a mixture to synthesise amino acids.
Hence, oxygen.
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