Something Rich and Strange : SEA CHANGE: A Message of the Oceans, <i> By Sylvia Earle (Putnam: $24.95; 336 pp.)</i>

Full fathom five my father lies;

Of his bones are coral made;

Those are pearls that were his eyes;

Nothing of him that doth fade,

But doth suffer a sea-change

Into something rich and strange.

The term sea change comes from this ditty, sung by Shakespeare’s water sprite Ariel in “The Tempest.” We use it now as a term to mean change so profound that one can scarcely grasp the relation between first and later forms.

It has great meaning in our time, when we are noticing all around us unexpected environmental changes, more shocking and irreversible than Shakespeare might have thought possible. A vast change in ourselves is called for, a sea change that will transform the scale and nature of our thinking and enable us to see our place in the world with eyes that are rich and new.

Can anything short of disaster bring about a comprehensive change in attitude? Sylvia Earle, in her new book about the world’s oceans, believes so. She believes that the basic cause of people’s indifference to the health of the sea--the source of all life--is ignorance. Ignorance can be overcome, and “Sea Change” is an effort in this direction.

Lighthearted, easy to read yet full of information, the book is drawn from the personal experience of a pioneer diver whose record-setting explorations have been coupled with superlative efforts in public information and conservation action.

“Sea Change” is, among other things, autobiography. Earle, born in 1936, was a child who loved swimming. She became a marine scientist and one of the top policy-makers in America for matters pertaining to the sea. As an explorer who needed better tools, she participated in experiments with every kind of diving gear and vessel, and in 1981 co-founded, with Graham Hawkes, the Deep Ocean Exploration and Research engineering firm of which she remains president.

We know very little about the sea because its exploration is technically difficult. Every descent requires equipment and expertise. Within 25 feet of the surface, one loses access not only to open air but also to 90% of the light, and as a diver descends, there are problems of increasing pressure. Few divers venture below 150 feet, although Earle has descended, solo, to more than 3,000.

To imagine the depth of our ignorance, one only has to know that the sea reaches 35,800 feet. The development of equipment that can convey and maintain explorers in the deep ocean is hugely expensive, and the biggest potential sponsors--governments--tend to favor support for what is known.

Thus, “instead of applying 95% of our scientific efforts to 95% of the biosphere,” writes Earle, “most of the attention has been and still is focused on the brightly illuminated surface in which humankind normally functions--a dangerously cavalier bias, given the utter dependence of the 5% on the rest.”

With so little information available, what we do know about the sea is amplified in its importance.

Earle’s more than 6,000 hours underwater and her years of effort to bring what she’s seen to our attention count for double because of the uniqueness of her experience. It is especially depressing, then, to hear from Earle that during the decades of her exploration, she has witnessed severe degradation in many of the places she has revisited. She grits her teeth and gives us the details in the second half of “Sea Change.” I can hardly bear to go on reading when I reach this section of the book.

But something in the author’s spirit, perhaps the vividness of her fight, leads me onward. She has had some success in encouraging people and organizations to take responsibility for their part in the deteriorating health of the ocean: She has urged the examination of areas subject to pollution--her description of the aftermath of the Persian Gulf oil spill, which she was invited to visit, is absolutely horrifying--and the creation of ocean sanctuaries analogous to national parks but bigger, on an international scale.

If one person’s efforts can achieve this much--and the reader is continually reminded that this person was also fighting discrimination against women--there is hope.

What engage me most intensely in “Sea Change” are the descriptions--too short, too often interrupted, as Earle’s dives must also seem to her--of a few of the extraordinary creatures and geological forms she has seen. These details leave me breathless with desire to learn. It is not because of what is being lost but because of what is being found, not because of what is dying or threatened but because of what is alive and well, that I wish for the survival of the Earth and am examining my own life for lifestyle changes I can make--sea changes, difficult but essential.

“Sea Change” amply reveals its author as a superstar, yet Earle writes comfortably and excludes no one from her readership. Here is how she ends the chapter entitled “Poisoning the Sea”: “Loss of horseshoe crabs might not seem like a big deal. I can imagine some of my cynical pals, drinking beer, munching pretzels, teasing me with killer questions, including the clincher: ‘Who cares? I don’t!’ ”

I can also imagine philosophical crabs, perched on their several-hundred-million-year record of success, disdainfully reviewing our meager history, thinking “Who cares? We don’t!”