The persistence of life measured by carbon cycling in closed ecological systems

Abstract

Materially closed energetically open ecological systems have been observed to support biological activity for over 10 years. It has been suggested that closed ecological systems (CES), as models of the earths biosphere, will support life indefinitely. Undefined excesses in the amount of bioelements included in the construction of the first studied CES have made it impossible to quantify the length of time for which life will persist in a CES. This work presents a metric which can be used to predict the length of time which biological activity can be expected to persist in a CES. This metric is based on the measurement of carbon biomass and carbon cycling rate in materially defined CES. Two independent methods, radiocarbon labeling and the increase in pressure in a CES from the accumulation of gaseous oxygen as a result of the reduction of carbon have been used. The turnover time of carbon is determined for a CES with a stable biomass and carbon cycling rate. Predictions are then made for the length of time that a detectable level of biological activity will exist in a CES. The CES containing a complex natural community are predicted to persist for a minimum of 6 years and perhaps indefinitely.