What is the maintenance of a fairly constant internal environment

Maintainance of constant internal environment is carried out in a process called Homeostasis.

Explanation:

Maintainance can of several types such as pH, temperature, and other substances such as Concentration of Ammonia in body. These all should maintain at constantly for stability in body. The maintenance of temperature is called thermo regulation.

i'd say that the moon rock is about 2.2 billion years old.