Evolution of life may have shaped Earth’s continents

New Scientist : The evolution of life on Earth may have affected more than just its atmosphere and oceans: It may also have decided the size and extent of the planet’s land masses. According to a recent paper published in Planetary and Space Science, two computer models show vastly different outcomes for Earth’s topography, depending on the presence or absence of early bioactivity. On an Earth where bacteria and other organisms develop and inhabit ancient land masses, such creatures tend to erode the surface and deposit the sediments into the oceans. As the sediments sink, the increasing thickness of the sedimentary layer that lies on top of the subducting oceanic slab prevents water from escaping the mantle material. The wetter the mantle, the more buoyant it becomes, and it eventually rises to the surface via volcanic eruptions. The model shows those eruptions extending the continental crust to cover as much as 40% of Earth’s surface, about what it does today. The Earth model without such biological activity, however, shows the buildup of much less continental crust, or even none at all—perhaps one vast water world dotted with volcanoes. While many researchers agree it is a good “thought experiment,” much remains to be learned about the geological processes that drive continental formation and the possible chemical weathering from other sources, such as acid rain.