Cells divide for many reasons. For example, when you skin your knee, cells divide to replace old, dead, or damaged cells. Cells also divide so living things can grow. When organisms grow, it isn't because cells are getting larger.
Answer:
Higher oxygen levels means animals can grow larger and still maintain the supply of oxygen to their muscles. Falkowski and colleagues calculated fluctuations in the atmosphere's oxygen levels from cores of deep-sea rocks dating back 205 million years.
