THE OTHER NIGHT I zipped open a plastic box of spinach and lifted out some leaves only to find big green wads of rotten spinach-mush lurking within. Sigh.

I’ll admit, I was consternated. Then I stopped myself.

Out the kitchen window, our garden was locked beneath a stratum of ice. Yet here sat plenty of still-edible young leaves, native to ancient Persia, grown in California, triple-washed by high-pressure sprayers, laid into a box made of translucent petroleum, trucked safely through blizzards and over mountain passes to my local Albertsons? And I was consternated that 30 percent of it had gone smooshy?

When did utter miracles start becoming banalities? Is this what turning forty is about? I resolved silently, over spinach salad, to make the following day—random Wednesday in January—Miracle Day. I would devote myself to identifying the miraculous. I would pay attention.

One way to celebrate Miracle Day is to imagine that one of your ancestors, a version of yourself that lived, say, twenty-seven thousand years ago—a caveman, if you must—is hanging out with you for the day.

Before dawn, my caveman and I bend to get the newspaper in the driveway when I notice six or seven white splotches of bird poop at the edge of the lawn, directly below the public streetlight. I look closer: a piece of a bird’s wing, feathers still attached, sits nearby. On the rim of the streetlight twenty feet above: more feathers.

An owl—gone now—must have eaten a songbird in the night. Inside, I was sweating through another night, and out here an owl was using the streetlight as his kitchen table. Miracle Number One.

My caveman, of course—far more engaged in the natural world than I could ever hope to be—noticed the bird carnage immediately. He’s more interested in modern wonders.

Yes, Mr. Caveman, this newspaper we’re holding contains color photographs of events that happened in Pakistan yesterday. Yes, I’m wearing socks fabricated by someone I’ve never met. Yes, I have lots of pairs of them!

Ten minutes later, my publicist e-mails me an itinerary. That’s correct, I receive in Idaho, instantaneously, a seven-page communiqué from a woman in New York City that arrives within a half second of her completing it. In your time, Mr. Caveman, the Late Pleistocene, she would have needed papermakers, holy men, soldiers, wagons, domesticated oxen, prayers, bribes, a shared language, fortitude, and lots of jerky to get that thing to me.

Now? Instantaneous! Miracle Number Seventeen.

Also: I don’t have polio. And my teeth are intact.

I brew tea grown in South Africa. My children leave for school in clothes made in Bangladesh. My caveman, by this point, will have had to take a brief spell in a dark closet. On Miracle Day, one can see too much.

After lunch, my caveman and I clamber onto a twin-engine turboprop bound for Seattle. Window seat, 9A. Propelled by the concentrated remains of ancient plants, the airplane hurtles down the runway at over one hundred miles per hour, soars through a thick layer of freezing mist, and slowly, beautifully, incredibly, rises toward the sun. For a half hour we ascend into a peacock blue sky while an ever-changing mat of clouds roils below.

Then a woman brings us ginger ale. With ice! Beside us a pregnant lady does Sudoku. We are going 220 miles per hour. I hear Louis C.K. in my head: You’re sitting in a chair in the sky. You’re like a Greek myth right now.

Eighty minutes later the plane door opens and we smell the sea. We have teleported into an altogether different climate. Miracle Number 21,315.

Within seconds of setting foot on the Seattle tarmac, I use my telephone (which also contains several novels written by dead Russians) to text my wife: Safe and sound on the ground. Eight seconds later, carried on light our eyes cannot see, nine smiley faces come winging back.

At a downtown hotel, a man with Alfonso on his name tag gives us a paper-thin magnet embedded in a stripe on a card. Elevators rocket us to the forty-sixth floor. I use the magnet to unlock a door. I take a shower. Remove all the steel, plastic, and glass around me, and I’m standing naked 450 feet above Westlake Square being pelted with hot water.

What are miracles? Miracles are avocados in winter and starling swarms and the handwriting of children. They’re bridges that let trucks carrying toilet paper for thousands zip across uncrossable rivers and books that contain the voices of the dead.

Once, my scientist brother showed me a housefly under an electron microscope. Savannahs of small hairs grew out of the fly’s nose. Rows of perfect domes arced over each compound eye. There was as much intricacy in a barb on one of the fly’s legs as there is in a Shakespearean sonnet.

The towels in my hotel room are deeply, amazingly white. The lotion smells like paradise.

We sit for a minute on the bed, my caveman and I, dusk on Miracle Day, the lamps off, and watch the Seattle skyline bloom out of the fog. Gulls cry invisibly. Out there, beyond my windows, people are eating ground-up cows from Argentina. They’re reading Whitman: Unscrew the locks from the doors! Unscrew the doors themselves from the jambs! They’re building towers of glass, dreaming of mackerel, studying gridlock, falling in love. Above us, above the mist, 50 sextillion Earth-like planets swing around 50 sextillion Sun-like suns. Galaxies fly away from us. Mica glitters on a trillion rocks.

My telephone rings, and I study it for a moment before answering. It’s as much curse as marvel: a wafer of glass and plastic that embodies rare mineral mining, carbon emissions, slave labor. And yet, when I answer, my sons want to show me, in real-time, the snow falling in our backyard five hundred miles away.

They hold the phone out into the darkness. I can just make out clumps of flakes falling on the foothills. Everything, if you study it closely enough, is a miracle.