It was Easter Sunday in the year 1960. After filling a 10-gallon glass carboy with some compost, David Latimer inserts a spiderwort sprout inside and seals the carboy shut. Latimer then places the carboy in a spot where it receives sunlight, turning it around every once in a while so that the sunlight is distributed evenly.
Twelve years later, in 1972, he opens it to add water and then seals it shut for the last time. For decades, the carboy has never been opened, yet life continues to thrive inside it. How does a closed ecosystem, such as the terrarium made by David Latimer, work?
What is a Closed Ecosystem?
An ecosystem is a space that consists of organisms and a physical environment and is defined by the interactions between the two.
The physical environment within an ecosystem functions through an exchange of matter between that specific physical environment, and its surrounding environments. Water, for instance, moves from one ecosystem to another through the water cycle.
A closed ecosystem, such as a terrarium, does not rely on this exchange of matter with external systems. Rather, a closed ecosystem only needs energy from the outside to become a self-sustaining ecosystem.
By providing energy, in the form of sunlight, to a closed ecosystem, the cycles needed to support an ecosystem are completed. They are the water cycle, the carbon and oxygen cycle, and the nutrient cycle.
The Water Cycle
Water is an essential part of all ecosystems. Normally, water is transported from one ecosystem to another. However, in Latimer’s terrarium, water cannot escape the sealed carboy.
Water in the compost is absorbed by the plants and released through evapotranspiration. The water molecules, which are now in vapor form, start to condense on the exposed surfaces when the temperature starts to cool down.
As the water accumulates through condensation, it starts to fall back down to the compost, where it will be once again absorbed by the plants.
The Carbon and Oxygen Cycle
Through a process known as photosynthesis, plants utilize energy from sunlight to convert absorbed water and carbon dioxide into glucose and oxygen molecules. The oxygen molecules are released into the atmosphere while the plants utilize glucose for growth and development.
The oxygen in the closed ecosystem is then utilized by the aerobic microorganisms that break down the carbon-rich plant matter. In the process of respiration, the microorganisms release carbon dioxide into the air, which in turn, is utilized by the plants during photosynthesis.
Through this cycle, the plants continue to supply oxygen to the microorganisms, while the microorganisms continue to break down the dead plant matter, releasing carbon dioxide in the process.
The Nutrient Cycle
Nutrients, such as nitrogen and phosphorus, are initially found in the compost present in the terrarium. Much like water and carbon, plants need these nutrients to grow and develop.
Microorganisms break apart and consume plant matter as the plants die and start to decay. The nutrients found in the decaying matter help some of the microorganisms develop and reproduce.
The nutrients are eventually released back into the compost, where they will be absorbed and utilized by the younger plants to fuel their growth.
Sunlight and Energy in a Closed Ecosystem
Energy is one of the key factors which makes an ecosystem work. Microorganisms inside the closed ecosystem receive energy from the plant matter that they break apart and consume.
Plants, on the other hand, receive energy from the sunlight. By adding energy to the ecosystem, the cycles can continue to function, thus sustaining the ecosystem. On the other hand, removing the supply of energy would cause the ecosystem to perish.
By providing energy to it, the terrarium becomes a representation of the earth and the ecosystems that thrive within it.