SACRAMENTO, Calif. — After 33 years of marriage, Martha McDowell's husband told her he wanted a divorce. He provided few reasons. They were trivial, and to her did not justify ending their union.

"He just didn't want to be married anymore," says McDowell, now 60. "But he was my best friend, and I expected to spend the rest of my life with him."

That was four and a half years ago. Today, McDowell, of Hayward, Calif., is a new woman. She is a grandmother and works for an arts college, a job she loves. She is active in her Fremont, Calif., church, and says it was her faith that helped her deal with the emotional issues that come with late-life divorce.

"My commitment to forgive was the most important thing for me," she says. "I didn't want to become bitter, and I didn't want my bitterness to poison my children."

Couples divorce every day. Yet it is particularly surprising when a marriage of more than 30 years ends. Take the recent announcement of Al and Tipper Gore's split. As the news spread, we felt a collective sense of sadness. What were they thinking? Why divorce after 40 years of marriage?

Late-life divorce is relatively uncommon. Sociologists agree that most people who have been married for a long time are happy. Nevertheless, some couples still drift. Marriages of 40 years or more account for 4 percent of divorces, according to Andrew Cherlin, a Johns Hopkins University sociology professor who studies families. It jumps to 8 percent for marriages of 30 to 39 years, likely because these couples are closer to life's empty nest stage, when children are grown and out of the house.

Late-life marriages dissolve for the same reasons any marriage does. Sometimes, there is abuse. Or infidelity. More often, the causes are even simpler: They grow apart, develop different goals, or no longer feel fulfilled. Contributing factors to late-life divorce, in particular, include increased life expectancy and longevity and a social acceptance of divorce that did not exist a generation ago, according to Beverly Hills Family Law Attorney Steven Knowles of Knowles Collum LLP.

Given the large size of the aging baby boomer population, this is somewhat new territory for sociologists, like Cherlin. After all, from an evolutionary perspective, the institution of marriage was designed to help you raise kids and put food on the table, he says.

"Only in the past half century have we had people who live long enough that they are together for 20 to 25 years after child-rearing," Cherlin says. "This is a new stage of life, and we're figuring out what to do with it." It used to be the middle aged who asked themselves, 'What should I do with my life?' Now, 60-year-olds do, he says.

Fifteen years ago, Al W.'s wife of 36 years filed for divorce. She was a stay-at-home mother of four sons and once they were grown and out of the house with children of their own, she wanted her independence to focus on a business venture, says Al, a retired pilot who asked that his last name be omitted to protect his family.

"She needed something more in life than coming home to me," says Al, now 70 and living in Pleasanton, Calif. "In hindsight, it was devastating. We didn't have a perfect marriage but I certainly thought we had a better relationship than a lot of our friends who stayed married."

Besides the financial aspect of a late-life divorce — "You're talking about (losing) half your retirement," Al says — the most difficult part for him was coming home to an empty house. Al eventually remarried and now has a 10-year-old daughter, who was born when he was 60.

"It was kind of late to start over but I wouldn't trade it for anything," he says. "I'm extremely happy." He has also remained friends with his ex-wife.

Divorce can be amicable if each person is mature enough to take responsibility for the reasons the marriage didn't work, says M. Sue Talia, a Danville, Calif., private family law judge, mediator, and former divorce attorney. Financial security and long-term spousal support are among the biggest issues in divorces that occur in or near the golden years.

"Suddenly, you have to go out and get a job," says Talia, author of "How to Avoid the Divorce from Hell (And Dance Together at Your Daughter's Wedding)" (Nexus Publishing Company, 2006). "A lot of the people who are getting divorced late in life have had to reduce their standard of living."

The year following her divorce, Connie Bates of Walnut Creek, Calif., had no choice but to move in with her son and his family in Patterson. She had been married for 36 years when her husband left. He wanted to be free, she says.

"I had to start from scratch," says Bates, who is now 55. "I had to get a car. I had to find an apartment. But there was a relief for me because I kind of always wanted to get out of it (the marriage). It was strained."

McDowell never wanted out of her marriage. The first four years following her divorce were challenging. She went into debt. She had to watch her finances to the point that she couldn't participate in certain social activities. But, through intense grieving and spiritual work, she is a stronger person today, she says. In particular, she credits the support of her friends.

For the first six months, McDowell had trouble being at home. She had lived in that house with her ex-husband for 28 years, after all, and everything, particularly the bedroom, brought back memories. It was hard to sleep at night. But redecorating wasn't exactly a priority.

So imagine her surprise when she came home from a trip to find her bedroom and bathroom completely redone. Her church friends had repainted the walls. They had put in new linens, bedding, window coverings, and a shower curtain. McDowell loved it.

"I remember coming home from the airport and thinking, 'I'm going to go back to all those memories.' But, it was all changed. Can you believe it? My friends uplifted me."

Gray divorce

Below are six contributing factors to late-life divorce, also known in family law circles as gray divorce, courtesy of Beverly Hills Family Law Attorney Steven Knowles of Knowles Collum LLP:

Increased infidelity in older adults. People 60 and older are having more extramarital affairs, according to a recent University of Washington study. It found the lifetime rate of infidelity for men over 60 increased to 28 percent in 2006, up from 20 percent in 1991. For women over 60, it was 15 percent, up from 5 percent in 1991.

Economic mobility. Women overall have increased financial independence.

Change of attitudes. Society's acceptance of divorce and the decreased social stigma.

Increased life expectancy. People are living longer and therefore choosing more fulfilling lifestyles.

Adult children. Parents are less concerned about the consequences of divorce for adult children.

Identity quest. Increased desire for personal freedom and exploration of identity later in life.

Distributed by McClatchy-Tribune Information Services.