date: 2012 July 23 (Mon) 16:00-17:00
room: CPS Conference Room
speaker: Yoshiyuki Tatsumi (Center for Planetary Science)
organizer: Ayako Suzuki
title: Why is this planet to be the Earth?
abstract: Why is this planet to be the Earth?
One characteristic feature of the Earth is the bimodal height distribution at the surface. This is caused by the difference both in density and thickness of the crust. Two types of crust on the Earth, the oceanic and continental crusts, have been created at divergent and convergent plate boundaries, respectively, via. plate tectonics. The essential cause of operation of plate tectonics is the temperature difference within the mantle, which triggers mantle convection. The upper thermal boundary layer of this convection corresponds to the lithospheric plate, but behaves naturally as a stagnant-lid, i.e., the plate should not move. The presence of liquid water at the surface, on the other hand, strongly reduces the yield strength and could cause the fracture within the stagnant-lid, triggering the plate subsidence or subduction. Parameters that govern the presence and absence of liquid water on the terrestrial planets are: the distance from the Sun and the mass of a planet. A conclusion of this consideration would be that the Earth is a shore planet because of the presence of the ocean, which seems to be a conclusion of a Zen dialog.
keywords: plate tectonics, mantle, continental crust, oceanic crust, convection, water, stagnant lid, yield strength, terrestrial planet, ocean