Photosynthesis puts oxygen in the atmosphere.
Since the question is incomplete, the answer will include the generalize ways that can be used to analyze evolutionary relatedness among gibbons, monkeys, and humans.
Answer:
The evolutionary relationship is important to understand the evolution of the organisms. The common ancestors and closely related species of the organisms can be known by study the evolutionary relationship of the organism.
The DNA sequence and the amino acid sequence of gibbons, monkeys, and humans are quite similar with each other. The gibbons and humans have more then 99% DNA sequence similarity. The physical characteristics, cranial capacity and anatomical characteristics of the gibbons, monkeys, and humans are more or less similar with each other.
A decrease in dissolved oxygen.
This is because oxygen is a byproduct of photosynthesis. If the plants are in water, some of the oxygen they produce will become dissolved in it. Without those plants, you have less dissolved oxygen.
