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S. Franck, A. Block, W. von Bloh, C. Bounama, H.-J. Schellnhuber, and Y. M. Svirezhev
Planetary and Space Science 48, 1099-1105 (2000)
Potsdam Institute for Climate Impact Research (PIK),
Telegrafenberg, P.O. Box 60 12 03,
14412 Potsdam, Germany.
We present a new conceptual Earth system model to investigate the long-term
co-evolution of geosphere and biosphere from the geological past up to 1.5
billion years into the planet's future. The model is based on the global
carbon cycle mediated by life and driven by increasing solar luminosity and
plate tectonics. As a major result of our investigation 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 different insolations. In this way, we can find the
habitable zone as the band of orbital distances from the Sun within which an
Earth-like planet might enjoy moderate surfac 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 500 Ma ago while the
position of Venus was always outside the habitable zone.
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