The Evolution Of The Terrestrial Environment

Abstract

Abstract The evolution of the Earth’s environment during its 4.6-b.y. history is investigated using a carbon cycle model in which the carbon is assumed to circulate among five reservoirs ( the atmosphere, ocean, continents, seafloor, and mantle). In this model, we consider continental weathering, carbonate precipitation in the ocean, carbonate accretion to the continents, metamorphism of carbonates following CO degassing through arc volcanism, carbon regassing into the mantle, and CO2 degassing from the mantle. We also take into account changes in external conditions such as an increase in the solar luminosity, continental growth, and a decrease in tectonic activity with time, which obviously affect the carbon cycle. We numerically calculate the temporal variation of the carbon content of each reservoir under varying external conditions over the entire history of the Earth. We find that continental growth is required for the terrestrial environment to evolve to the present state, and that the carbon cycle has had an important role in stabilizing the surface temperature of the Earth throughout its entire history. The distribution of carbon at the surface is mainly controlled by one parameter, an accretion ratio, which represents the fraction of the seafloor carbonates accreted to the continents. When this value is equal to 0.7, correct values for the present distribution of carbon at the surface of the Earth can be obtained from the model.