Inputs, Outputs & Closed Systems: Lessons from Biosphere 2

Closed Systems Defined: Exchange only energy (e.g., solar energy in, heat energy out) across their boundary, not matter.
Examples: The Earth (in terms of nutrient cycles, as nutrients remain on Earth), a sealed terrarium, and Biosphere 2.
Nutrient Cycles: All essential nutrients (e.g., nitrogen, carbon) on Earth stay on Earth and constantly cycle among organisms, water, and soil.

Purpose: A human-made, entirely sealed miniature world ( $3$ acres) in Arizona, built to test the feasibility of creating self-sustaining ecosystems for long-term human habitation in space (e.g., Mars).
Structure: Contained various biomes (rainforest, ocean, savannah, marsh, desert), an agricultural area, and a human habitat, all sealed with steel and glass.
Key Challenge - Oxygen Depletion: Oxygen levels significantly dropped from $21$ % to $14.2$ % unexpectedly. The cause was identified as $CO_2$ (from the breakdown of compost in the soil) reacting with exposed concrete, sequestering the oxygen.
Human Impact: Participants experienced physiological effects like gasping for breath and cognitive impairment due to low oxygen.
Outcome: The issue was identified and understood, proving the concept was viable with adjustments. The experiment highlighted the complexity and delicate balance of Earth's biosphere.

Interconnectedness: Emphasized the literal and visceral connection between organisms and their environment, demonstrating material cycling (e.g., breathing out $CO_2$ that feeds plants, then eating those plants).
Earth as Biosphere 1: Provided a comparative understanding of Earth's natural systems, where humans have a significant impact.
Future Applications: Led to research on smaller biospheres for space stations and sustainable industrial ecosystems that convert pollution into resources (e.g., using shrimp farm effluent to grow crops and mangroves in desert environments).
Individual Impact: Encourages recognition that small actions contribute to the larger biosphere, promoting a shift towards a "biophilic" (life-nurturing) society.