Which of the answers below is the best example of a positive feed back that then reaches an equilibrium in an Earth system?

A. The slow growth in diversity of the biosphere until it reached a balanced equilibrium.
B. Unfortunately, humans have been killing off species and upsetting this global balance.
C. The slow melting of the ice caps at the end of the ice age and then their equilibrium in the last 10,000 years after the ice age (at least until humans start shrinking the ice caps with global warming).
D. The slow buildup and then maintenance of stratospheric ozone (at least until humans got involved).
E. The slow buildup of the magnetosphere and then its maintenance (thank goodness humans can't affect this Earth system).

The Earth since it was formed it had different stages, in some the temperature is was so hot (in the ancient atmosphere) and in another ages it was so cold (in all the ancient ice ages). So, since the formation of Earth as a planet, the temperature changes was a fact until can reach an average temperature thanks to an stable atmosphere and the great biodiversity that contribute to an equilibrium in the distribution of the elements in air, soil and water (like the photosynthesis and respiration process).