At first glance, the miracles in Karen Thompson Walker’s haunting first novel don’t seem particularly miraculous. They are the ordinary events of early adolescence, so basic that only later is their value apparent. A best friend moves away – then comes back. A snow day cancels school, and all the kids go sledding. A quiet, lovely boy with shaggy hair and long eyelashes reveals that he knows you exist.

Ordinarily, such moments fade quickly as life hurtles on. But in the extraordinary, awful world of “The Age of Miracles,” these happy fragments emerge starkly. Life is changing. Maybe it’s ending. One Saturday, the world wakes up to discover that the earth’s rotation has inexplicably begun to slow. Expectations of time quickly shatter. Days grow long. Nights, too. Nobody knows exactly when to go to school or work or bed. That snow day? It happens in beachside California.

“We did not sense at first the extra time, bulging from the smooth edge of each day like a tumor blooming beneath skin,” Julia, our observant young narrator, tells us. But suddenly everything is different – and daunting.

“The Age of Miracles” is a poignant hybrid, a sci-fi/coming of age novel that celebrates human resilience even as it breaks your heart. The subject matter invites comparisons to Tom Perrotta’s more raucous “The Leftovers,” in which several million people vanish from Earth without explanation and those left behind must carry on in the face of the unknown.

“The Age of Miracles,” though, isn’t a satire. Smartly and compassionately executed by Walker, a former Simon & Schuster publicist who lives in Brooklyn, the book is a heartfelt story told in a reverent, elegiac tone. Julia is looking back on the events she describes as she and her parents and friends try to navigate the new world order.

“It’s never the disasters you see coming that finally come to pass,” she says sagely. “It’s the ones you don’t expect at all.”

Julia could be talking about the end of the world as she knows it or her changing fortunes in sixth grade. That’s part of Walker’s genius: For Julia – for anyone, really – adjusting to the minefield of adolescence is just as tricky as adjusting to the apocalypse. Time stretches in puzzling ways; new interests and allegiances form. Best friends fall away. Boys are growing taller. Girls are wearing bras and makeup.

“(E)verything around me was about to come apart,” Julia says, and she’s not just referring to the fact that some of her neighbors have packed up and fled or that others have rebelled against “clock time,” choosing instead to live by the altered rhythms of the sun. Upheaval is the new normal in every facet of her life.

Walker gets around the scientific specifics of her fantastic premise by using a young girl to tell the story; Julia only knows what she hears on television and what she can observe. TV news tells her that scientists remain baffled by the phenomenon. She witnesses decline firsthand: Birds drop from the sky. Whales beach themselves on the shore near her house. Even people behave differently: “We took more risks. Desires were less checked. Temptation was harder to resist.” Her mother hoards canned food. Her father drifts away. Who’s to say if the slowing earth is the cause of all of these shifts?

The novel’s wondrous momentum rolls on with the insistence of the restless surf that swallows the beachfront homes; you can’t stop reading if you try. Walker refuses easy solutions, instead offering up the revolutionary and bittersweet idea that stolen moments can give any life meaning: a few hours learning to ride a skateboard; running on the beach with a boy you’re half in love with; the cool, sweet taste of the last grape you ever eat. Miracles do happen, she seems to say. You just have to know where to look.