Redi's experiment on biogenesis involved placing dead animals in open and closed bottles to observe the presence of maggots, demonstrating that life does not spontaneously arise from non-living matter. The main objection from supporters of abiogenesis was the claim that oxygen was necessary for the process of reproduction, which they believed was not adequately accounted for in Redi's setup. Critics argued that the closed bottles lacked oxygen, potentially skewing the results. At the time, belief in abiogenesis was prevalent, leading to resistance against Redi's conclusions. This historical debate highlights the tension between emerging scientific evidence and established beliefs in biology.