Educational Model: Oxygen Revolution
The model demonstrates some stages of a key change in Earth’s history caused by the activity of living organisms.
This model is a component of the IUMC (Innovative Educational and Methodological Complex) "Ecology: Constructing the Biosphere", developed in 2008 by D. A. Shabanov, A. G. Kozlenko, and M. A. Kravchenko by order of the NTFP (National Training Foundation) of the Russian Federation (more about this project is in the article "Innovation and Reality"; reasons why this complex is not used are briefly described in the column "Textbooks: Straight into the Day After Tomorrow"). This model is posted here for educational use. The model demonstrates some stages of a key change in Earth’s history caused by the activity of living organisms. The theoretical material related to the model is presented in the supplement "Some Stages in the History of Life on Earth" of the manual "Ecology: Biology of Interactions". The model demonstrates the replacement of groups of photosynthetic organisms in Earth’s history, the causes of this replacement, and its influence on the planet’s appearance. During the existence of the early biosphere, the atmosphere of young Earth, like its entire surface, had a reducing character. Reducing gases (CH4, NH3, and others) were emitted from Earth’s interior, and substances capable of binding oxygen were dissolved in ocean water (for example, Fe2+ salts, which oxidize to Fe3+ in the presence of O2). Under these conditions, the first photosynthetic organisms appeared. These were anaerobic cyanobacteria. Oxygen was a toxic metabolic product for them. Accumulation of oxygen near bacterial cells (in the model shown as a blue "cloud" near bacteria) inhibited their growth. From a certain time onward, aerobic (adapted to existence in oxygen-containing environments) photosynthetic organisms began to dominate in the biosphere. These include certain groups of cyanobacteria and plants, for example green algae. Instructions for working with the model are located at the very bottom of its window; if these instructions do not fit in the small box, they can be scrolled up and down with the arrows on the right. Some tasks that can be solved while working with the model: 1. Using the model, determine the conditions under which aerobic organisms can spread in an evolving biosphere. Describe the nature of the relationship between anaerobic and aerobic photosynthesizers. Track changing parameter values using graphs. Note that the graphs are in arbitrary units. 2. Pay attention to changes in water and sky color. Explain what causes these changes.