Alright, I woke up refreshed this morning, so here's all the information from page 40:
World Establishment (development materials)
Gaia and Terra
Gaia
The world that serves as the stage for FFIX. In its civilization, machines are becoming more dominant than magic. Its civilization is young yet -- covering only a portion of the planet's surface.
Terra
A world with a highly advanced magical civilization. Terra's people made use of the ultimate magical art, Fusion, in order to attain eternal life. In modern times, Garland watches over the people of Terra until the Fusion process ends and the day comes that they awaken once more.
Fusion
Fusion is cast when the crystal of the world of Terra's people becomes old. They seek out young planets whose cores have not yet grown through receiving the experiences of living things, assimilating the pure crystals of such young worlds and circulating the power of souls through each person of Terra to finish the process -- this is Fusion.
Crystals
At the center of planets, the presence which governs the cycle of souls. Crystals send out souls to be born as living creatures, and when they die, the memories from their lifetimes are sent back to the crystal with their souls. Crystals grow through the accumulation of these memories, and from these complexities, are able to create ever more complex creatures. As crystals grow, their radiance increases and the planet becomes richer. If the circulation should become unable to continue, the accumulation of memory ends, the planet begins to decay, and the crystal itself is returned to the cosmos along with the planet.
Gaia's crystal has a blue radiance, while Terra's crystal has a red radiance.
The fusion of Gaia and Terra
Unable to find a young planet with a pure crystal, Garland was driven to the limit and had no choice but to select the young planet Gaia for Fusion. [See Figure 1]
However, Gaia's crystal was not pure and rejected the process; Gaia's entire civilization was destroyed in the subsequent cataclysm, and the surface of the world was left in ruin.
The effect of the incomplete Fusion on living creatures and nature was the production of many sub-races, as well as several structures from Terra shifting to the surface of Gaia; as for Terra itself, it was shifted inside of Gaia. Also, because of the incomplete Fusion, Terra's moon remained and adjusted to Gaia's original, giving Gaia two moons.
The moons receive their crystals' radiance, which is why Gaia's moon is blue and Terra's moon is dyed red. Also, in the sea near Esto Gaza is "the Shimmering Island," the "interval of both dimensions (Gaia and Terra)," where the radiance of the crystals emanates (for more details on the moons, refer to P.43, "The relationship between the moons and the radiance of the crystals"
.
In order to facilitate the recovery of the ruined environment, Garland transplanted Terra's magical tree Iifa to Gaia. This incident was 5000 years ago.
http://img145.imageshack.us/img145/520/terraandgaiarp7.jpg
[Figure 1] Picture from development (Illustration: Hideo Minaba)
Gaia World
•The Shimmering Island (portal entrance) [top arrow]
•Gaia's moon
•Overlap of both dimensions
•Gaia's crystal [bottom arrow]
The Iifa Tree [the "bridge" in the middle of the diagram]
Terra World
•Overlap of both dimensions
•The Shimmering Island (portal exit) [top arrow]
•Terra's moon
•Terra's crystal [bottom arrow]
So there we go. Basically just a confirmation of most of what OWA-2 quoted earlier, though it didn't include the detail that crystals turn red when a planet is dying. Maybe that's on page 43 or was just what that other person thought it indicated. Right now I think that their natural color (blue, red, green, whatever) just grows brighter or dimmer depending on how healthy the planet is.
I'll translate page 43 later and find out.
One interesting detail to come out of this is that the Iifa Tree apparently existed on Terra before the cataclysm, and Garland just moved it over to Gaia.
Put together with the information from the timeline, it seems the Iifa Tree's purpose for some 4200 years was just to encourage the regrowth of Gaia's environment. It was only 800 years before the game that Garland created the Soul Divider (whether that be Necron or whatever).