Eureka! Scientists just discovered that Comets on Fire is the missing link in rock 'n' roll evolution. The hard-hitting noiseniks provide the connection between late-'60s vintage Grateful Dead and Paranoid-era Black Sabbath, long theorized but until now never established. A few savvy researchers, including Comets themselves, saw this coming: The San Francisco Bay Area five-piece is indigenous to the Dead's original stomping grounds, and its earlier records were blues-based, psych-metal monuments, full of deafening riffs, droning electronic ambiance, and relentlessly hypnotic rhythms. With Avatar, Comets back off the volume, distill the distortion into eerie filigree, and take a logical step toward sonic refinement. Imagine Tommy Iomi jamming on Anthem of the Sun, the Dead's weird, trebly, 1967 studio joint. It's all there on Avatar wiry, dual guitar interplay, muddled vocals, choogling bass lines, a sense of dark, open-ended experimentation tucked into cogent, six- to eight-minute songs. If you're a metal fan and snicker at the Dead's freewheeling ethic, you might rue the influence, but you can't deny it. And if you're a Deadhead, try something a little heavier. Both camps can come together and hesh out/get high to Comets on Fire. And the boys at the lab already proved you all have the same haircuts anyway.