From the Tunguska Space Body to the Evolution of the Protoplanetary Nebula . ... A model for the structure of comet nuclei is proposed based on the results of the investigations of carbonaceous substances from the epicenter of the Tunguska cosmic body (TCB) explosion. ... Editorial note: This paper suggests several new ideas about the solar nebula and the formation and composition of comet nuclei based on investigations of the Tunguska event. ...