New kelp fossils may help explain the Pacific Ocean's underwater jungles

MARY LOUISE KELLY, HOST:

The kelp forests that hug the Pacific coastline are an underwater jungle, a thicket of colossal algae intermixed with a pageant of life - snails, urchins, sea lions, sea otters. Now there's new proof that the first kelps were much older than we once suspected, arriving well before many of their present-day animal inhabitants. Here's science reporter Ari Daniel.

ARI DANIEL, BYLINE: Jim Goedert is a retired railroad signal inspector. He lives outside of Tacoma, Wash., where he regularly drives up to the north side of the Olympic Peninsula to go for walks along the rocky shoreline.

JIM GOEDERT: Gray whales and seals come in, and occasionally orcas. There are kelp beds offshore, some nice beach platforms, you know, at low tide exposed. That's when we do the collecting, is low tide.

DANIEL: Collecting of fossils. At low tide, the beach is set like a table with them, including these hard, round masses.

GOEDERT: We would crack these open, and sometimes there's a crab or some other fossil in these rocks. But I would find these little squiggly veins or roots. I couldn't really tell what they were.

DANIEL: Then one day, during a break on one of his beach walks, Goedert came across a mound that had washed ashore of kelp holdfasts, the root-like structures that fasten the towering algae to the seafloor.

GOEDERT: And I thought, that's what that thing is - kelp. It was just an aha moment.

DANIEL: Goedert packed up some of his best specimens, drove to the post office and shipped them to Stockholm, to a professional - Steffen Kiel.

STEFFEN KIEL: He just kept sending me holdfasts. I just left it alone for a few years 'cause, as usual, I had other things to do. Sometimes they were, like, not showing much new, and sometimes they were like, wow.

DANIEL: Kiel is a senior curator at the Swedish Museum of Natural History and a colleague of Goedert's. Kelp fossils are exceedingly rare, in large part because they're so soft and squidgy. Years ago, researchers used a single specimen to estimate that complex kelp emerged at least 13 or 14 million years ago. More recently, genetics helped push that date back to at least 30 million years. But there was no fossil evidence to back that number up, which made Kiel wonder about the samples he'd received.

KIEL: I looked at them and cut them in half and polished the surface.

DANIEL: Do you happen to have any of those fossils near you?

KIEL: Yeah. Hang on.

DANIEL: Kiel grabs a couple fossils out of a file cabinet.

KIEL: OK.

DANIEL: On one, a splotch of root-like tendrils appears to be draped across the rock.

KIEL: That's the holdfast. I have various specimens where they were sitting on a bivalve shell, on a clam shell or especially often on barnacles.

DANIEL: Kiel took one of those fossilized shells that the kelp had glued itself to and performed a special chemical analysis on it to determine its age.

KIEL: We then knew exactly - pretty much exactly - that these fossils were 32 million years old, no doubt about it.

DANIEL: Thirty-two million years old - that confirms the earlier genetics work, but the fossils are stronger proof that complex kelp date back to the early Oligocene, a time of dramatic global cooling.

KIEL: The whole world's oceans got a hell lot colder right at that time. Kelp like it cold, so that was a perfect fit.

DANIEL: The fact that complex kelp have been around for so long means a couple things. First, it helps resolve a puzzle about an ancient vegetarian marine mammal related to today's manatees - the desmostylian.

KIEL: People were wondering what they were actually feeding on 30 million years ago, and now our kelp fossils show, yeah, desmostylians most likely were happily feeding on this kelp.

DANIEL: Here's the second insight. For millions of years, the kelp ecosystem was quite simple, with the kelps themselves being somewhat short, maybe a few feet tall. Then around 14 million years ago, much taller kelps evolved, forming the underwater forests we know today, and a thriving hub of biodiversity gradually began to materialize.

KIEL: All these animals that characterize modern kelp ecosystems full with all sorts of life.

DANIEL: The results are published in the journal PNAS.

CERIDWEN FRASER: I have been approached before by people who thought they had kelp fossils, and I wasn't convinced. But what we're looking at are very clearly kelp.

DANIEL: Ceridwen Fraser is a marine scientist at the University of Otago in New Zealand who wasn't involved in the research. She studies kelp evolution and how its DNA mutates, something she anchors in time using the fossil record.

FRASER: And the annoying thing about kelp is there's hardly anything known from the fossil record. So this will be a tool that I can use now.

DANIEL: As for Steffen Keil, he's delighted that once again, fossils have taught him a familiar yet fundamental lesson about our world.

KIEL: An archive of Earth history, of life through Earth history - that's what fossils are to me.

DANIEL: An archive that sometimes washes ashore where all you have to do is look for it.

For NPR News, I'm Ari Daniel. Transcript provided by NPR, Copyright NPR.