Lesley Stahl knows momentous.

The 12-Emmy-winning “60 Minutes” correspondent has interviewed Margaret Thatcher, Yasser Arafat, Boris Yeltsin and multiple U.S. presidents, including Donald Trump in his first television interview as president-elect.

She’s reported from Guantanamo Bay prison, the Middle East, a nuclear missile control center and Ground Zero after the Sept. 11 terror attacks.

Decades ago, when her daughter, Taylor, turned 4, Stahl recalls, “I threw her fourth-birthday party on the beach with a cake, a clown and Sam Donaldson.”

But a career filled with big names and big events did nothing to prepare Stahl for the shock and awww! she would feel when she became a grandparent.

“I was bowled over,” she told me recently. “I didn’t expect it. No one warned me. It hit with a wallop, and I was so surprised by the power of it.”

Taylor, Stahl’s only child, is now grown and married, with two daughters of her own: Jordan and Chloe. Stahl writes about the ways her granddaughters have changed her life and worldview in “Becoming Grandma: The Joys and Science of the New Grandparenting” (Blue Rider Press.

The book explores everything from the chemical changes that occur in your body when you first hold your grandchild (stronger than romantic love) to the evolving role that modern grandparents play, now that they’re living longer and healthier, on average, than previous generations.

“Here we are trying to figure out what we’re going to do with these healthy years,” Stahl said. “And here are these grandchildren and children who really need our help.”

High-powered careers are often still in the mix when grandchildren arrive, which was rarely the case for the women in Stahl’s mother’s and grandmother’s generation.

“We’re part of the first generation of grandmothers who are not defined by our family roles,” Stahl writes. “Having been those pioneers in the white-collar workplace, we have a professional identity. And yet … we’re the ones going bananas over our grandchildren.”

It’s a tricky setup, without question. But it can be a winning one, Stahl argues, if grandparenting takes top priority.

Grandparents and grandchildren both benefit physically and emotionally from spending time together, and Stahl writes about the healing properties her two grandchildren appear to pass along to her husband, Aaron Latham, who has Parkinson’s disease.

Their two granddaughters benefit as well.

“Researchers have found that grandchildren who have a close relationship with a grandfather are likely to perform well in school, display positive emotional adjustment, have higher self-esteem and a greater ability to develop and maintain friendships,” Stahl writes.

Stahl is careful not to assume her experience is universal. She interviews grandparents and children from various cultures and socioeconomic backgrounds. She explores stepgrandparenting.

She connects with women who’d rather get a facial than play house with the grandkids, and she travels to rural and urban group homes where children without access to their biological grandparents connect with elderly residents to gain the love and lessons they would otherwise miss.

But for grandparents who are able, the book is an unabashed call-to-arms.

“If you’re not already pitching in, start now,” she writes. “Become actively engaged in your grandchildren’s lives. If you’re already babysitting and sending money, do more. If you live in another state, build into your retirement plan a way to be with those children more often. And if the path to your own grandchildren is blocked for whatever reason, then get involved helping other young children.”

Linda Fried, dean of Columbia University’s school of public health, told Stahl, “The elderly are the only increasing natural resource in the entire world.”

“We’re a surplus value,” Stahl writes. “Using that value to help grandchildren is a perfect solution, and the advantages for our overly stretched daughters, daughters-in-law, sons and sons-in-law are immeasurable.”