By the power of truth, I, while living, have conquered the universe.
Because you touch yourself at night...
The Halos were given, in your words, "nature" surfaces to support catalogued specimens the Librarian had collected. However, the Master Builder intended them to be infected by the captive Flood contained on the rings, then subsequently terminated in order to test the Halos' effectiveness.
Also, the weather and environment system was designed to test the limits of the Flood super cell.
[Edited on 08.01.2011 5:28 AM PDT]