The spell requires a rank 4 green (Earth archmage) to cast as well, cost 300 mana, and is (I'm guessing) 25% there at the very end of the magic tree.
This is my suggestion, (and i really wish spells could scale up like that, with 2 colors, but that's another debate)
Terraforming 1
Prerequisites: - Life1 apprentice + Earth1 Apprentice
Cost: 50 mana for a 2x2 Square
Effect: Tree regrow from dead tree, for the purpose of having a wood mill, no city spot revealed
Terraforming 2
Prerequisites: -Life2 disciple + Earth2 disciple
- Terraforming 1
Cost: 100 mana for a 3X3 Square
Effect: Potential city spots are revealed, tree regrow from dead trees
Bonus effect: extra food if cast on a city (mana maintenance: 1)
Terraforming 3
Prerequisites: - Life3 Mage + Earth3 Mage
- Terraforming 2
Cost: 200 mana for a 4X4 Square
Bonus effect: Extra material if cast on a city (mana maintenance: 1)
Terraforming 4
Prerequisites: - Life4 Archmage + Earth4 Archmage
- Terraforming 4
Cost: 300 mana for a 5X5 Square
Bonus effect: Extra essence if cast on a city (mana maintenance: 1)
Terraforming 5 (GAIA)
Prerequisites: - Life5 master+ Earth5 master
- Terraforming 4
Cost: 500 mana for a the whole map
All cities are under the effect of terraforming 1, terraforming 2 and terraforming 3 (all terraforming mana maintenance are waved)
Be cool