Death metal was born after 1982, when Discharge, Amebix, the Exploited and G.B.H. refined the techniques of extreme music. Bands like Bathory, Slayer and Hellhammer then mixed metal's epic riff styles with the new punk nihilism to invent underground metal.

That was in 1983-1984. The following year, Sepultura released Morbid Visions/Bestial Devastation and Possessed released Seven Churches, both of which were death metal in its fully mature form. The year after that, Morbid Angel unleashed one of the first truly progressive death metal album with Abominations of Desolation. At that point, the genre was well-defined.

Old school death metal tends to use a lot of tremolo picking, simple riffs in weird combinations that make psychedelic songs, and doomy, booming extended passages. It is the antithesis of commercially-friendly music.