Habitable zone for Earth-like planets in the solar system

We present a new conceptual Earth system model to investigate the long-term co-evolution of geosphere and biosphere from the geological past upto 1.5 billion years into the planet’s future. The model is based on the global carbon cycle as mediated by life and driven by increasing solar luminosity and plate tectonics. As a major result of our investigations we calculate the “terrestrial life corridor”, i.e. the biogeophysical domain supporting a photosynthesis-based ecosphere during planetary history and future. Furthermore, we calculate the behavior of our virtual Earth system at various distances from the Sun, using di erent insolations. In this way, we can nd the habitable zone as the band of orbital distances from the Sun within which an Earth-like planet might enjoy moderate surface temperatures and CO2-partial pressures needed for advanced life forms. We calculate an optimum position at 1.08 astronomical units for an Earth-like planet at which the biosphere would realize the maximum life span. According to our results, an Earth-like planet at Martian distance would have been habitable up to about 500 Ma ago while the position of Venus was always outside the habitable zone. c © 2000 Elsevier Science Ltd. All rights reserved.