Planet Millennium’s internal structure has evolved differently than Earth’s. Although Millennium has major volcanic activity, the planet does not experience sea-floor spreading or continental drift. Millennium’s one super continent has maintained its shape and location since the creation of the planet.

Unlike the Earth’s mantle (solid iron and magnesium-rich silicate minerals), Millennium’s porous mantle contains vast mineral deposits layered throughout her igneous, sedimentary, and metamorphic rock strata. The only significant density change occurs in Millennium’s predominantly liquid core—molten iron and nickel. The center core comprises about one-fourth of the planet’s density, the other three-fourths exists as mantle and crust. The mantle of Millennium, surrounding the super-hot core, constitutes the bulk of the planet—83% of her volume and 76% of her mass. The mantle is porous—like a gigantic sponge.

The porosity of Millennium’s mantle and crust are the direct result of magmatic intrusions from the hot core, followed by billions of years of erosion from subsurface water and wind systems. The geological result: gigantic magma chambers, fissures, caves, tunnels, and sinkholes throughout the three major subterranean strata.

Six millenni-miles deep, three distinct strata—layers—form the Underworld of Answers. The layered realms have evolved geologically (as well as geographically), different. Each of the three stratum varies in thickness, from 1 millenni-mile to 3 millenni-miles deep.

The First Stratum, known as the Realm of the Crystal, begins at Millennium’s surface and extends to a depth of 1 millenni-mile. The Second Stratum, the Realm of the Dungeons, measures 2 millenni-miles deep. The Third Stratum, known as the Realm of the Utmost Darkness, measures 3 millenni-miles deep and ends 2 millenni-miles above the Crater of Chaos floor. 

All three strata support fantastic life forms and spectacular topography.

The Crater of Chaos, Planet Millennium’s most notable geographical land feature, exposes the three strata—the porous mantle—to the Upperworld of Wisdom. Appearing as an enormous symmetrical hole in the middle of the planet, the crater walls stand deeper than the three strata combined, 8 millenni-miles deep. The one-of-a-kind topography carved into the vertical cliffs of the crater expose thousands of caves, caverns, grottoes, and eight major falls—the southern Falls of Fire and the northern Falls of Ice being the most spectacular.

So goes the Underworld of Answers.

So goes Planet Millennium.

--- Octilogy : Part III - Chapter XV