It's suspiciously easy to overlook the existential side of Boise, Idaho's Built To Spill, a seasoned but frequently rotating ensemble centered on avuncular frontman Doug Martsch. There are brighter enticements to the band's amiably fractured rock: Martsch's arresting guitar solos, the songs' devil-may-care structural assembly, the whole package's never-duplicated ability to channel Neil Young and the Pixies and the Butthole Surfers, sometimes within the same phrase. Nevertheless, there's always been a surprisingly dark coffeehouse-philosopher vibe underneath all the winning quirks — it's even implicit in the band's name.

Untethered Moon, Built To Spill's eighth studio album (featuring a new rhythm section in bassist Jason Albertini and drummer Stephen Gere, both former BTS roadies), lays those questing tendencies as bare as any before it. Picking up the moody threads of its predecessor, 2009's There Is No Enemy, the record focuses sharply on the various kinds of cosmic disquiet that come with, as "Living Zoo" puts it, "being a human / being an animal, too." The first act tackles notions of civic unrest, immortality through art and the perishability of memory; all of this before culminating, in "Some Other Song," with a note of touching vulnerability: "I don't know how to not fall apart / Please tell me how to never fall apart."

From there, the songs don't so much lighten up as allow the music to carry more of the weight of these bemused ruminations. Between "C.R.E.B.," a high-strung meditation on the treachery of the brain, and rumbling closer "When I'm Blind," the album's ambience becomes by turns melancholy and sinister, casting an appealing pall over Untethered Moon — and, if you let it, over the sum of Built To Spill's two-decade output. That's hardly a bad thing, especially for a band whose sound remains approachable and organic in such a rare way. The album rages, but not with anger or sadness; just with life itself.

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