Sol: Destroyer of Worlds

The Desert Planet

Even if the biosphere can resist against the decline of CO2 concentrations, water available and air temperatures will ultimately doom life on Earth. As current reservoirs of water on Earth are enormous, it may surprise you to know that we are constantly losing water to mantle region below the crust. Subduction zones, areas where oceanic plates are forced under continental crust, are effectively drains for surface water. The oceanic crust is not surprising water logged, and the water content of the plate is subducted along with the plate itself. However, this mechanism will "only" remove approximately 27% of our current ocean water over the next billion years. However, beginning in about 1.3 billion years, temperatures in Earth's atmosphere will likely reach 320K. This value is a critical threshold, as above that point, we will transition to a moist greenhouse atmosphere.

The moist greenhouse atmosphere is important for multiple reasons. Water is an incredibly effective greenhouse gas, so as the oceans evaporate the air will heat even faster in a runaway cycle that results in the eventual complete evaporation of all ocean water. Of course, that water vapor has to go somewhere, and it ends up going high into the atmosphere where intense high-energy solar radiation can dissociate the hydrogen and oxygen atoms. Hydrogen is then irreversibly lost as it is light enough to escape the gravitational attraction of Earth, and water cannot reform. Eventually, Earth will become a dry desert planet.

The evolution of ocean water mass as solar luminosity increases. (from Bounama, Franck & von Bloh)

Surprisingly, even this cataclysmic event may not completely destroy the biosphere, as water supplied from the subsurface may allow simple life to persist. But the Sun will ultimately have its way.

References

Kasting, J.F. Icarus 74, 472-494 (1988).

Bounama, C., Franck, S. & von Bloh, W. Hyd. and Earth Sys. Sci. 5, 569-575 (2001).

This website designed by Brian Vanderwende, 2012.