In [u]The Wounded Land[/u] was wrote:"It is said that in generations past each new sun shone for five and six, even as many as seven days. But a sun of four days is now uncommon. And with my own eyes I have beheld only one sun of less than three."
I imagine that the Sunbane came on slow and sneaky. It started out as an imperceptible aura, with imperceptible effects. As it got stronger, it became more perceptible.
Possibly also, there was no clear delineation of phases early on. It was just present as a whole. As it grew stronger, it began to sort itself out, and begin dividing into different phases. At first the phases were not clearly seperate - for example, the rain phase may have been rain and pestilence and fertility and desert all at the same time, but was more rain than anything else. Perhaps there were other phases which withered away rather than became stronger.
For it is corruption. Like rot, it attempts to penetrate everything, and it grows in some places but not on others. The Sunbane rot took hold in the elements of rain, pestilence, fertility, and desert, and grew stronger there.
Over time, the phases strengthened. The delineations became clearer. The phase of rain became half rain, then mostly rain, then entirely rain. Stronger and Stronger.
And as it became stronger, it speeded up. When the phase of rain held sway, all the other phases were too strong to wait their turn. They fought each other for dominance. The stronger they got, the less time each phase held sway over the others.
- - - - -
As for the forests, well, it probably was some sort of tipover point. Early on, the forests healed themselves faster than the Sunbane could corrupt them. But they got farther and farther behind. One day, the damage reaches 100% ... and then they sloughed to the ground.
Did every tree and plant die at the same time? I think Covenant imagines it to be so, but it probably was not. It probably fell in pieces over time.
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