Short answers, pulled from the story.
Archaeologists Petros Themelis and Maria Siganidou found the Derveni papyrus on the 15th of January 1962 inside a nobleman's grave near Derveni. The scroll survived because it had been carbonized by the funeral pyre that consumed the body below.
The surviving pieces of the Derveni papyrus sit under glass in the Archaeological Museum of Thessaloniki today. Many smaller shards remain unplaced even after decades of work since its discovery.
Zeus gains authority by hearing oracles delivered directly from the sanctuary of Nyx herself according to the narrative described inside the roll. He then rapes his mother Rhea leading to Demeter's birth before raping Demeter resulting in Persephone's arrival.
T. Kouremenos G.M. Parássoglou and K. Tsantsanoglou edited this landmark volume which was published through Casa Editrice Leo S. Olschki. A team led by A. L. Pierris assembled in 2005 with Dirk Obbink from Oxford University to study the fragments.
The fire turned the fragile plant material into something hard and black much like charcoal during the burning process that consumed the body below. The ink on the surface also turned black during the burning process so both the background and the writing shared the same dark color.