Tangerine Dream’s third album, 1972’s Zeit, is a landmark of dark ambient music, spinning the krautrock impulses of their first two LPs into ominous abstraction. In “Birth of Liquid Plejades,” quivering strings set the somber mood before celestial organs and spectral wails soar skyward; “Nebulous Dawn” deploys blackened drones and gurgling sound effects to suggest noxious alien atmospheres. The closing “Zeit” might be the spookiest of them all, as eerie wails float sorrowfully against a backdrop of pure, shimmering dissonance.