Final answer:
The relationship between atmospheric oxygen concentration and extinction events is complex and influenced by various factors. Evolutionary adaptations, such as changes in red blood cell efficiency, can occur in response to lower oxygen levels. However, the current mass extinction is more directly linked to climate change and habitat loss than to atmospheric oxygen concentration itself.
Step-by-step explanation:
The relationship between atmospheric oxygen concentration and extinction events is not straightforward and can vary depending on many factors. In terms of available oxygen in the past, for example, there is evidence of lower oxygen concentrations during the time of the dinosaurs due to high volcanic activity. If atmospheric oxygen levels were lower, the red blood cells in dinosaurs might have evolved to be larger or more efficient at carrying oxygen to adapt to a lower-oxygen atmosphere. In the context of extinction events, climate change and habitat loss, driven by human activities and the increase in atmospheric CO₂, are more directly linked to the current period of mass extinction rather than the concentration of atmospheric oxygen. Changes in atmospheric oxygen have occurred over Earth's history and have influenced the evolution of life, but directly correlating these concentrations with widespread extinction events is complex.