WIthout convection the earth as a whole takes longer to cool down but the surface layer cools faster. In an earth with a convective mantle the earth as a whole cools faster but the surface layer cools slower (because it is receiving more heat from the core).
This article helped me understand that back in the day: www.blc.arizona.edu/courses/schaffer/449/England%20-%20Perrys%20Neglected%20Critique.pdf
This article helped me understand that back in the day: www.blc.arizona.edu/courses/schaffer/449/England%20-%20Perrys%20Neglected%20Critique.pdf