Sylvia Earle, at work. (Google Earth)

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Oceanographer and explorer Sylvia Earle went down to the sea when sea exploration was a man’s world — and she made it her own.

She walked the ocean floor untethered deeper than any human before or since. Lived and dived and explored beneath the sea all over the world. Helped change our understanding of the watery mass and life of the Earth — and is still doing that today.

At 73, she is the driving force behind the new Google Earth Oceans feature. And she’s still diving.

This hour, On Point: Explorer Sylvia Earle on a life in the sea.

You can join the conversation. Are you a diver? A deep sea diver? What do you see going on in our oceans? What’s your question for the woman who has lived there?

-Tom Ashbrook

Guest:

Sylvia Earle is Explorer-in-Residence at National Geographic and co-author of “Ocean: An Illustrated Atlas.”  She’s lead advisor on the new Google Earth Ocean layer, and a 2009 TED prize recipient.  A pioneering and record-setting deep diver, she has logged over 6,000 hours underwater and led more than 50 expeditions, including the first team of women aquanauts during the 1970 Tektite Project.

More links:

Download Google Earth 5.0, and take Sylvia’s Ocean Tour here.  You can also explore sea ice and pollution in near real-time with gadgets from the Google Earth Gallery.

Learn more about deepwater corals and Thunder Bay Sinkholes at NOAA Ocean Explorer.

“Each man kills the thing he loves,” said Oscar Wilde, and that is certainly true — man, woman and child — when it comes to tuna.

The world’s favorite fish is so popular — in tuna sandwiches, in sushi bars, in cat food — that we are, as a species, loving it to death. We harpoon it, hook it, net it, and increasingly ranch it, in giant pens at sea. Tuna cowboys haul it in by hand, by the gills.

The great ones are all but gone — and we’ll talk today with the man who caught the biggest ever: fifteen hundred pounds of tuna. A new book says the rest could go the way of the buffalo.

This hour, On Point: The fate of the tuna.

Can you picture the world without tuna, without a tuna sandwich? Will the tuna go the way of the buffalo? Has tuna always seemed to you like an infinite resource, a commodity that could never run out? Will the last great slice of the last tuna be gobbled up at a sushi bar in Tokyo? Have you fished tuna — with harpoon, rod and reel, net? Do you worry about the mercury, and if so, how much? How do you see the fate of the tuna? Tell us what you think.

-Tom Ashbrook

Guests:

Joining us in the studio is Richard Ellis, an author and marine artist who has written and illustrated for National Geographic, Discover, and Scientific American. He’s written up whales, squid, and shark. His new book is “Tuna: A Love Story.” You can read an excerpt at RandomHouse.com.

And with us from Novo Scotia is Ken Fraser, the man who holds the world record for the largest tuna ever caught: 1,496 lbs. He’s the author of “Possessed,” a book about the world of bluefin fishing.

Ken Fraser with the largest tuna ever caught, off Nova Scotia in 1979.

Here’s a YouTube clip from the new TV show “Tuna Wranglers,” which follows the lives and exploits of tuna ranchers as they transport vast schools of tuna in huge floating pens:

For a long, long time, the world’s oceans have seemed just too vast to be seriously affected by the hand of humankind. The endless rolling waves, the briny depths, the creatures beyond number — all these seemed to dwarf our footprints on the beach and ships at sea.

No more. A new global mapping of human impact on the world’s oceans brings home just how thoroughly our fishing and trawling and dumping and warming have reshaped the oceans. It’s an astonishing picture.

This hour, On Point: Mile by mile, mapping the human impact on the deep blue sea.

-Tom Ashbrook

Guests:

Andrew Revkin, environment reporter for The New York Times and author of “The North Pole Was Here: Puzzles and Perils at the Top of the World.”

Dr. Benjamin Halpern, marine biologist at the National Center for Ecological Analysis and Synthesis at the University of California, Santa Barbara, and lead author of “A Global Map of Human Impact on Marine Ecosystems,” published last month in the journal Science.

Kevin Speer, oceanographer aboard the Roger Revelle in the Antarctic, focusing on ocean currents, temperature and salinity.

Tim Battista, oceanographer aboard the Nancy Foster off the coast of Puerto Rico, he and his team of researchers are mapping the damage done to coral reefs.

David Ho, researcher aboard the Ronald H. Brown in the Antarctic, studying how greenhouse gasses move between the atmosphere and ocean.