Earth is a closed system. That means the amount of rocks, metals, carbon, nitrogen, oxygen, and water on Earth . So, it is essential that biogeochemical cycles these materials as they move through Earth's subsystems.

The Earth is a "closed system" which means that the amount of rocks,  carbon, metals, nitrogen, water and oxygen on earth remains constant. So it is essential that "biogeochemical cycles renew these materials" as they move through the Earth's subsystems.

Hoped this helped, brainliest me?

answer; i do believe its (b) 12.5 years of age;