  Is the present-day water-land ratio a necessary outcome of the evolution of
plate tectonic planets with a similar age, volume, mass, and total water
inventory as the Earth? This would be the case - largely independent of initial
conditions - if Earth's present-day continental volume were at a stable unique
equilibrium with strong self-regulating mechanisms of continental growth
steering the evolution to this state. In this paper, we question this
conjecture. Instead we suggest that positive feedbacks in the plate tectonics
model of continental production and erosion may dominate and show that such a
model can explain the history of continental growth.
  We investigate the main mechanisms that contribute to the growth of the
volume of the continental crust. In particular, we analyze the effect of the
oceanic plate speed, depending on the area and thickness of thermally
insulating continents, on production and erosion mechanisms. Effects that cause
larger continental production rates for larger values of continental volume are
positive feedbacks. In contrast, negative feedbacks act to stabilize the
continental volume. They are provided by the increase of the rate of surface
erosion, subduction erosion, and crustal delamination with the continental
volume. We systematically analyze the strengths of positive and negative
feedback contributions to the growth of the continental crust. Although the
strengths of some feedbacks depend on poorly known parameters, we conclude that
a net predominance of positive feedbacks is plausible. We explore the effect of
the combined feedback strength on the feasibility of modeling the observed
small positive net continental growth rate over the past 2-3 billion years.
