The evidence that best supports the student’s claim that "life is possible because of the unique mixture of gases that cycle through the Earth’s spheres" is:
a diagram illustrating how plants use carbon dioxide, water, and sunlight to produce food and oxygen gas.
This evidence directly relates to the role of gases in sustaining life, as it demonstrates the process of photosynthesis, where plants convert carbon dioxide and sunlight into oxygen and food, illustrating the importance of these gases in supporting life on Earth.