How did the appearance of microbial life on land increase the formation of a living soil during early earth, which in turn allowed for the evolution of land plants? a) microbes allowed plants to uptake oxygen-containing compounds through the process of oxygen fixation. b) microbes allowed plants to uptake carbon-containing compounds through the process of carbon fixation. c) microbes allowed plants to uptake hydrogen-containing compounds through the process of hydrogen fixation. d) microbes allowed plants to uptake nitrogen-containing compounds through the process of nitrogen fixation.