Ray Kinsella: What?

Mann: You're from the '60s.

Kinsella: Well, yeah, actually . . .

Mann: Out! Back to the '60s! Back!

- From Field of Dreams

Many of us who qualify for Senior status are, indeed, from those dreaded 1960s, or at least watched them pass with a combination of amusement and horror. Whatever else that decade was - and it was far more complicated than historical snippets or the fictional Terence Mann let on - it certainly was a time when a significant number of people were ready to invest weeks and even years in doing good things in places that weren't necessarily comfortable.

That readiness hasn't left some of us.

One of the four of us measuring the widths of trees in a patch of Everglades jungle a dozen years ago was in her 30s. Two others were at least 50.

And then there was Christina Hobbs.

"I've always liked being where people are doing things," said Hobbs, then and now an activist in New England gardening circles. "Really doing things."

Back then, Chris Hobbs was 70 and making her first Earthwatch expedition. Mary Rowe has been on 34.

"We have a volunteer in her early 90s," says Rowe, a volunteer-adviser for Earthwatch. "We have a few in their 80s."

Since 1971, the nonprofit Earthwatch (www.earthwatch.org; 1-800-776-0188) has sent its volunteer teams to 35 states and more than 100 countries to assist in field research and conservation projects that range from observing fur seals in Alaska to counting crocodiles in Zambia to cataloging remnants of a castle in Tuscany.

Nearly 40 percent of its 4,000 volunteers are 50 and older; more than 20 percent are at least 60.

"They often bring a sort of maturity and patience," Rowe, 48, says of the older volunteers. "A lot of them have a lot of knowledge they've accumulated over the years, which is helpful in all sorts of things, from team-building skills to things that are specifically helpful to the project."

The projects, from the United States to Mongolia, typically are hands-on: gathering, counting, measuring.

Our team in Florida's Everglades assisted a researcher in measuring the impact of a hurricane (Andrew) on pine trees. For two weeks, we lived with the researcher in a reasonably comfortable house in Key Largo.

By day, we went into the Everglades and measured the trees' thickness, with the researcher comparing our measurements to his. The data would assist in reforestation and ecosystem management.