Ten years ago this October I remember thinking, how did it get to be fall again?

I was driving to Surry through copper-colored trees and autumn-brown fields to visit a friend who was preparing to flee the lifelong Maine winter. The year 2018 seemed like a date in some Sufi eternity that I might never encounter anyway.

Ten years before that, in the old millennium, I remembered thinking, how did it get to be 1998 all of a sudden? We had recently come home from two roughhouse years in Bulgaria, of all places. I was wondering if I would ever teach again. In 1998, 2008 seemed like a distant ice age — after all, our 7-year-old son, Jack, would be on deck to graduate from high school. How would that ever happen?

Now, in 2018, he has a little son who’s nearly 2. What the …

Years pass like seasons. They pile up gradually like waves on a beach until suddenly it’s high tide. How does it happen?

It’s not that I can’t remember the water being halfway up the beach. I can. Between 1998 and 2008, we watched the first red sun of the new millennium rise over Belfast, flew across the Pacific Ocean to China, drove Jack’s high school band to their gigs in the gym. I remember a trip to Florida in November 2012 for my niece’s wedding, the warm green contrast with the tree-skeleton chill of Maine. This summer we visited Jack in Las Vegas, where the hot weather withered me.

Fall 1978: A Halloween day drive from the apartment in Portland through the brown meadow grass of southern Maine to Portsmouth, with Tom Rush singing “Urge for Going” over and over and over. Fall 1968: Less distinct, but I remember playing a million games of driveway basketball with frozen hands. The fall of 1958 I know mainly by hearsay — I recall the autumn woods of Chebeague Island being intensely gorgeous, though I don’t remember thinking so. I remember my sister and me running around in it.

Fall that day was early morning to two little kids.

Life moves like a year. The average lifespan in Maine was 79.2 years at last tally. Rounding it to, let’s say in all optimism, 80, a life span has four parts, the way 12 months have four parts.

The span from birth to age 20 is one-quarter of this average lifetime, like the first three months are one-quarter of a year. You’re born in a world of light and dark like January, sleep a lot, and grow in winter daylight. At 6 or 7, your lifetime’s first month has passed. At about 13 you’ve reached the end of February. Daylight is increasing. The ache and turmoil of adolescence are exactly like the thaw, mud and awakening of March.

Turning 20 is a windy April Fool’s Day, and 25 to 30 blossom like cherry May, where the slamdance and lilacs live. In June you climb into the full, high sunlight of your 30s.

July begins the flight through your 40s and high summer heat. It’s not that it never rains, and sometimes even hails. Jack at 4 slept in my arms in the back of a leaky Bulgarian van during an August thunderstorm. I protected his head from the drops. By eighth month’s end comes the deep green foliage of half a century. In the clear September air and reddening leaves, is visible all of what came before.

In October, you start to think about the coming cold, and the world settles down to retire. A sudden storm can wither and strip the fading leaves in a single night. Mid-November is 70, with chills that stiffen your limbs, and sometimes snow. In December, the light bends toward last ebb. Then at Christmas, unseen, the sun rekindles.

In the morning you held green leaves, and by evening they were brown and crumbled in your hand. How does the tide go out so quick?

Dana Wilde lives in Troy. His recent book is “Summer to Fall: Notes and Numina from the Maine Woods.” You can contact him at naturalist1@dwildepress.net. Backyard Naturalist appears the second and fourth Thursdays each month.