Answer
The atmospheric oxygen during carboniferous period is increased due to extensive photosynthesis by the plants as plants released oxygen during photosynthesis. The carbon dioxide level decreased because of the poor activity of the decomposers. In the absence of greenhouse gases, the global temperature lowered down.
Work Step by Step
The decomposition rate depends on a number of factors like availability of oxygen, microorganisms, and warm humid conditions. During carboniferous period, vast oxygen-deficit swamps were formed, which probably extracted oxygen generated from the photosynthesis. This resulted in the slow decomposition rate and led to an accumulation of the vast biomass. The compressed biomass gave rise to the fossil fuels later on.
The action of microorganisms on the dead organic matter leads to release of carbon dioxide during decomposition. Thus, the level of carbon dioxide in the atmosphere decreased simultaneously due to low decomposition rate.
The outgoing solar radiations (long wavelength) are trapped by the gases present in the atmosphere, which warms the atmosphere and the surface of the Earth. This phenomenon is also referred to as the greenhouse effect, in which carbon dioxide is a major contributor. In the absence or low concentration of carbon dioxide, the temperature of the Earth dropped down in the Carboniferous period.
