According to the words spoken by
Kouzou Fuyutsuki in episode 26', the opening of the
Chamber of
Gaf is
synonymous with the opening of the door to the world's
beginning and end. When this door opened, the surface of the
Earth turned to
LCL, and people were also no longer able to maintain their
individual life forms and were reduced to
LCL.
Ritsuko Akagi also spoke of the Chamber of Gaf in
Evangelion episode 23.
Source: The End of Evangelion : Glossary contained within The End of Evangelion - Theatrical Program.