Dinosaurs and several other prehistoric animals grew to be gigantic in their time. Ultimately, most animals in the past are significantly larger than the animals now. One largely recognized theory is that the level of oxygen is a major factor for this contrast in sizes. Taking this theory into consideration, is it possible for animals (and plants) to gradually evolve into larger sizes when the oxygen level is increased? Take for example a theoretical experiment inside a large dome or a controlled environment where oxygen levels are maintained at a high level. Does the abundance of oxygen entail a gradual growth in the size of the organisms (over generations) assuming that this abundance does not affect them fatally?
Yes, my focus was on the animals which are in the same controlled environment as the plants so I was thinking that the higher levels of oxygen, considering the theory stated above, would also affect the plants in some way through its co-existence with the directly affected animals.
Jehron:
In order to address your question you need to understand what Galileo Galilei had stated long ago: "Nothing is big or Small except by comparison". This implies that one needs to apply "Relative Magnitude" concept to understand Size. If we apply this concept you would find the Life invisible to unaided human eye could have Giant entities like giant Viruses, Bacteria etc. Although elevated levels of Oxygen in the geologic record has been linked to major turnover of life, but the evidence is not so straightforward (see link). Increased levels of Oxygen would have no impact on the size of the Life on planet earth.:
Best
Syed
http://www.pnas.org/content/111/11/3907.full
http://www.dinosaurtheory.com/scaling.html
For already hundreds millions years, dioxygen is no more a critical resource for aerial life. It may be in some anoxyc areas of seas.
But now, in quaternary era with glaciations, carbon dioxyde is a rarefied and critical resource for 98 % of aerial plants.
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