Dependence of Biological Activity on the Surface Water Fraction of Planets

TL;DR

This paper explores how the proportion of land and water on exoplanets influences the potential for complex biospheres and technological evolution, suggesting optimal conditions for life exist within a specific water fraction range.

Contribution

It introduces a model linking surface water fraction to biosphere development, highlighting a narrow optimal range for complex life and technological emergence.

Findings

Sparse biospheres on planets dominated by land or water

Optimal water fraction range for complex life is 30-90%

Implications for detecting life based on surface water fraction

Abstract

One of the unique features associated with the Earth is that the fraction of its surface covered by land is comparable to that spanned by its oceans and other water bodies. Here, we investigate how extraterrestrial biospheres depend on the ratio of the surficial land and water fractions. We find that worlds that are overwhelmingly dominated by landmasses or oceans are likely to have sparse biospheres. Our analysis suggests that major evolutionary events such as the buildup of O$_2$ in the atmosphere and the emergence of technological intelligence might be relatively feasible only on a small subset of worlds with surface water fractions ranging approximately between $30\%$ and $90\%$. We also discuss how our predictions can be evaluated by future observations, and the implications for the prevalence of microbial and technological species in the Universe.