The long-term climate evolution and planetary habitability – Onset timing of the plate tectonics in early Earth

The plate tectonics is an essential geophysical/geological process on the deep mantle water and carbon cycling, which may also control the long-term climate evolution because the volcanic degassing induced by the plate subduction seems to change the atmospheric condition. However, as suggested by the geological evidence on the onset timing of the plate tectonics in early Earth, which is modeled by the transition from the stagnant lid tectonics to the plate subduction, this timing may have great uncertainty. Here, two questions are addressed: 1. How can the deep mantle volatile cycling would be affected by the onset timing of the plate tectonics in the planetary system evolution?; 2. As a result of the successful scenario of the deep mantle volatile cycling explained for the observational constraints of the subduction flux of the water and carbon, how can the climate evolution be responded as a function of the history of the deep mantle volatile cycling such as the subduction flux? To address these questions, a simplified model of whole planetary system evolution based on the thermal history computation of the silicate mantle coupled with the energy balance climate evolution and deep mantle volatile is used with controlling both heat transfer and volatile cycling associated with the transition between stagnant lid and plate tectonics.

 

The main result indicates that plate tectonics may be essential for the mild and stable climate that allows having liquid water over billions of years of the time scale. This is because a sufficient amount of volcanic degassing can be found for the vigorous plate tectonics rather than the stagnant lid state to get the long-term mild climate. For the stagnant lid state, the snowball limit cycle can be found. Thus, the vigorous plate motion may contribute to stabilizing the warm climate.

 

To find out the constraint on the present-day surface environment, the transition timing from the stagnant lid to the vigorous plate subduction for explaining the present-day amount of volatiles and their subduction flux would range from 1 to 3 Ga. And, around 5 to 10 ocean masses of the water in the total planetary system is required so that the deep mantle melting should be continuously found to supply the volatile component to the atmosphere associated with the plate subduction, which is worked for the reducing the melting temperature of the silicate mantle. However, the subduction flux for finding the mild climate is one to two orders of magnitude larger than the expected from the geological constraint – 10¹² to 10¹³ kg/yr as well as some difficulty for explaining the global sea-level change. In the presentation, some improvements on including the big storage capacity of the volatiles in the mantle transition zone will be provided for giving a better understanding of both the deep mantle volatile cycle and climate evolution in the plate-mantle evolution system.