"Lichens that cover rocks provide constant moisture that can weaken rock, while acid from bacteria can dissolve rock," Spohn said.
These sediments are up to 40 percent water by weight. This means sediment that gets subducted can ferry huge amounts of water into the mantle layer that lies between the Earth's crust and core. Once this sediment reaches the pressure and heat found at depths of about 60 miles (100 kilometers), it releases its water, reducing the melting temperature of the surrounding rock. This leads more rock to melt and rise, eventually bursting from volcanoes as lava that helps add to continental mass. In other words, although life helps wear continents down, it also helps build continents up.According to the researchers' computer models, a planet with a wet mantle had 40% land mass coverage after 4 billion years, but a dry mantle (simulating a planet without life) only had 5% continental coverage.