Washington - What with the Big Spill and the Big Split, Americans are in a deep funk these days.

How could the combined might of American technology and the full force of the White House not be able to fix a broken oil pipe? And how could former vice-president Al Gore's storybook marriage, one that apparently inspired the Erich Segal cult novel Love Story, come to an abrupt end?

In a country long inured to the daily destruction of celebrity marriages, the Gores' split-up has left millions wondering: Is nothing safe or sacred any more?

This was, after all, a 40-year union.

And this was how Mr Gore, in the midst of his 2000 presidential election campaign, described his marriage with Tipper: It's 'a communion that just became a lot deeper and broader to the point where I wouldn't and couldn't consider a major life decision without her deep involvement'.

Little was revealed in the announcement of their separation other than that there was no third party involved.

For sure, the couple had weathered their share of ups and downs: A car accident that nearly killed their youngest child; the years of lonely weekends that the conscientious Senator Gore spent with constituents in Tennessee rather than with his family in DC; Tipper's long battle with depression.

So what gave?

If trends are a clue, a recent survey showed that women initiate two-thirds of divorces among older couples, making it more likely that it was Tipper who decided enough was enough.

If infidelity was not the issue, did they simply run out of things that glue two people together?

Psychologists like Ms Renana Brooks say a new 'glue' - a common purpose - is needed every time couples transit to a new stage in their marriage cycle.

After seven years, romance is not enough. After 20 years, the children can't be the crutch. And by the 40th year, the grandchild phase is over too. What then?

Unlike the Clintons whose shared passion is politics, the Gores were in many ways opposites in temperament who yet found themselves drawn to each other from their high school prom.

He was the straight guy who relished intellectual debates; she would have chosen roller-skating. He was groomed to be a politician; she never believed she would be a politician's wife. Now, he is always on the road, promoting his environmental cause; she wants the stillness to pursue photography.

Maybe it was just the curse of being married in the wrong decade.

From 1960 to 1980, the American divorce rate more than doubled - from 9.2 divorces per 1,000 married women to 22.6 divorces per 1,000 married women.

Fewer than one in five of couples who married in 1950 ended up divorced against about 50 per cent of couples who married in 1970. The odds were stacked against the Gores.

The couples minted in the 1970s ushered in a divorce revolution with the soulmate model of marriage, says Mr Bradford Wilcox, director of the National Marriage Project at the University of Virginia and a senior fellow at the Institute for American Values.

One's primary obligation was not to one's family but to one's self, the new model held.

Marital success was defined not by successfully meeting obligations to one's spouse and children but by a strong sense of subjective happiness in marriage - usually to be found in and through an intense emotional relationship with one's spouse.

So if the Gores subscribed to this model even as they lived through the decades, divorce was always going to be much more likely than among those wedded to the earlier institutional model of marriage.

'Divorce was not only an individual right but also a psychological resource,' says social historian Barbara Dafoe Whitehead, quoted in Mr Wilcox's paper on the evolution of divorce.

'The dissolution of marriage offered the chance to make oneself over from the inside out, to refurbish and express the inner self, and to acquire certain valuable psychological assets and competencies, such as initiative, assertiveness, and a stronger and better self-image.'

This sense of striving for a fresh lease on life and greater longevity could be what is driving the rising divorce rates among older people, the Times of London noted.

In 2007, the latest figures available in Britain, 50 per cent more over-60s got divorced than 10 years previously.

Ms Christine Northam, a marriage counsellor, said of the rising numbers of 60-somethings divorcing: 'I think that it has something to do with the changing role of women. They may have stayed together for the children, but after the children have gone, women are looking for more self-fulfilment... In their 50s and 60s, they realise they may have another 30 years of active life.'

Milan Kundera, in his novel Immortality, posed a question: If, after death, you had the opportunity of coming back and have the same life partner for another 40 years, would you? For many seniors in unhappy marriages, it would seem the decision is to split now before the end comes.

And yet it is ironic that the Gores' separation comes amid a counter-trend. Contemporary America has begun swinging back to supporting intact families. This is particularly so among the white, college-educated, affluent Americans, among whom divorces are at all-time lows.

To this 'back to tradition' crowd, the Al and Tipper Gore divorce is shocking, an inconvenient message that no marriage is safe.

If there is a lesson from the Gore break-up, some experts say, it is that with marriage, you are never done working on it.

Research from Stony Brook University in New York suggests that couples who regularly do new and different things together are happier than those who repeat the same old habits. The theory is that new experiences activate the dopamine system and mimic the brain chemistry of early romantic love, The New York Times reported.

Says Ms Stephanie Coontz, a marriage historian at Evergreen State College in Olympia, Washington: 'I think the warning we should take from this is not that marriages are doomed, but that you can't skate indefinitely and be doing different things and not really be paying attention to the marriage itself.'

This article was first published in The Straits Times.