Thrash, just like any heavy metal subgenre, wasn’t born overnight; it took years of experimentation by the forefathers, and younger artists taking notes and woodshedding ideas before a recognizable new style coalesced.

For the purposes of this list, we're retroactively giving Metallica credit for crystallizing the style’s core sonic ingredients on 1983’s Kill ‘em All. Everything here predates that album.

Now, not everyone will agree that that particular record should represent thrash’s "day one," but you have to start somewhere -- just as we metal-heads often choose to start heavy metal’s history with Black Sabbath because they fused countless preceding experiments into an unprecedented, consistently forceful sound.

That sound, as we all know, was also dominated by slow tempos at first, except for rare galloping passages and the odd faster number like “Paranoid,” and years would pass before enough groups shifted into faster gears, warranting a separate designation – “speed metal" -- which eventually influenced thrash.

Here, then, is a list key tracks that introduced thrash-like ingredients to heavy metal before thrash became “a thing.” The list consists of several expected, familiar faces, but also a few surprises that, while certainly subjective (as all things are), paints a fascinatingly frantic story in the era before thrash.

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