THE SOLAR SYSTEM FORMED BY THE CONDENSATION OF THE SOLAR NEBULA - A GAS CLOUD

THE PLANETS ACCRETED FROM THE NEBULA AS SMALL PLANETESIMALS CLUMPED UP

THESE "PROTOPLANETS" HEATED UP AND DIFFERENTIATED AS THE DENSE MATERIAL SANK TO THE CENTER, GIVING THE ROCKY CRUST AND MANTLE AND THE IRON CORE

COOLING CONTINUES TODAY AS CONVECTION AND PLATE TECTONICS

THE EXTENT TO WHICH CONVECTION CONTINUES CAUSES THE DIFFERENCES BETWEEN EARTH (active), MARS (dead), VENUS (in between?), MERCURY (dead)