∙After every rainstorm, an earthy smell will fill the air, summoning memories of gardens and lazy summers at the cottage. People refer to that “after-rain” smell but scientists call it petrichor, an aromatic mixture that includes chemicals produced by actinomycetes, a bacterium often found in soil.

At the University of Illinois at Chicago, that musky scent will occasionally waft through Murphy’s lab. Murphy collects actinomycetes found in oceans and lakes; his lab houses some 1,000 strains, found everywhere from Lake Huron to Vietnam’s Van Phong Bay.

For a chemist on a quest for antibiotics, actinomycetes are an obvious place to look. These are the bacteria that gave the world streptomycin, the first major antibiotic discovered after penicillin and the first to treat tuberculosis, which was once North America’s leading cause of death.

More than half of all antibiotics discovered since have come from actinomycetes. “I always describe these guys as the Rocky Balboa of bacteria,” Murphy says.

Streptomycin was discovered in 1943 by Albert Schatz, a Rutgers University student working under microbiologist Selman Waksman, the “father of antibiotics.” Schatz did not have to travel far to make history — he found the bacterium that produces streptomycin on his New Jersey campus. One strain was growing in soil; another came from the throat of a chicken from the Rutgers’ farm.

Streptomycin’s discovery won Waksman a Nobel Prize and unleashed a flurry of antibiotic exploration. But more than 70 years later, drug companies have long abandoned their search of the soil, realizing they were no longer finding anything new.

This is why scientists like Murphy are searching underwater — and travelling much farther afield.

A sleep-deprived Murphy arrives in Reykjavik, Iceland, after a 10-hour journey, his bag filled with breathing regulators, scuba masks and a diving suit designed to withstand frigid Icelandic waters. The son of a crane operator and a nurse, Murphy was raised in a bedroom community of Boston, meaning he is a chemist who says “cah-bin” instead of “carbon.” While he once wanted to become a firefighter, Murphy more resembles a camp counsellor: energetic, enthusiastic and clean cut.

His travel partner is his 34-year-old graduate student Michael Mullowney, a tall, bearded fellow with an arm cuff tattoo and an indie music T-shirt featuring a white rabbit he had drawn — a nod to his other life as an illustrator. Mullowney, a father of two, worked in bars, restaurants and a Los Angeles recording studio before discovering pharmacognosy — the study of medicines derived from natural sources.

The two are picked up at the airport by Sesselja Omarsdottir, their Icelandic research collaborator and a 39-year-old associate professor of pharmaceutical science at the University of Iceland. For the next two weeks, they will travel together, live together and dive together in their underwater pursuit.

This is Murphy’s second trip to Iceland. Last year, he and Omarsdottir mostly dove off the northern coast. This time, they drive five hours from Reykjavik to the Westfjords, the “dragon’s head” peninsula jutting out from Iceland’s northwest corner.

Geologically speaking, the Westfjords are the oldest part of Iceland and one of its most sparsely inhabited regions; the drive is such a solitary experience that hours pass without seeing other cars. Their destination: a fishing village called Drangsnes, population 71.

Outside the car window, the landscape is dotted with sheep, long-maned Icelandic horses and clues as to why they have come to the land of fire and ice for their scientific expedition. A red line streaked across a rocky cliff face offers evidence of an ancient volcanic eruption; a cloud of steam rising from the valley marks an escape route for heat stored in the Earth’s core.

“Iceland is a big geothermal site so there’s a lot of volcanic activity,” Murphy explains. “This creates a really dynamic environment and ... new types of life that might not exist elsewhere on the planet.”

Omarsdottir, who lives in Reykjavik with her husband and two children, adds that Iceland is also perched at a unique location, where two underwater ridges meet. There are warm water masses travelling from the south, mixing with Arctic water from the north, she says.

More excitingly, for a trio of aquatic drug explorers, the waters here are virtually untouched.

“If you just look at the (scientific) literature, there are very few publications that discover any natural products around Iceland,” Omarsdottir says. “This is a very unexplored area, with a different environment.”

As Murphy naps and Mullowney eagerly takes in the views — this is his first overseas trip since high school — Omarsdottir is behind the wheel, scanning the horizon with her scientist’s eye, searching for signs of unusual microbial life.

As they approach Drangsnes, she slams on the brakes. Murphy, still asleep in the back seat, jackknifes forward.

“Sorry, Brian,” Omarsdottir singsongs, reversing the car. But Murphy is already alert and peering out the window for what could have caught her eye.

They pull over near a calm inlet encircled by low mountains. Everyone scrambles over the rocky edge toward the water and Omarsdottir goes quiet, her cheeks flushed. “I’ve never seen a site like this before,” she says.

At the water’s edge, there is a flat, rocky clearing, the foundation of something built long ago. There is a square structure resembling the ruins of a large chimney and the rotten-egg smell of sulphur wafts through the air.

Something is growing here. The lava rock is streaked with red, white and green and a fuzzy lime-coloured film floats in shallow pools of water — cyanobacteria, Omarsdottir thinks, a bacterium that is sometimes toxic but has recently shown potential as a source of medicine. They scrape some into a plastic collection tube, one of hundreds they have packed for this trip.

Steam rises from the water. “Be careful,” Omarsdottir warns, as Murphy goes to touch a shallow pool — this is definitely a geothermal hot spot. She has a theory for what that large chimney-like structure is.

“You know what I think it is? A pool. A hot tub,” she says. Some Icelandic villager, probably from the early 20th century, took advantage of this natural heat source and constructed a pool for geothermal bathing, a favourite pastime for Icelanders.

The sulphur, the thermal heat, the cyanobacteria, the freshwater mixing with the salt — these are all clues that, microbially speaking, “only something very unusual would survive under these conditions,” Mullowney says.

They decide to come back and dive here. The shore is already interesting — what might the deeper waters bring?

“This is a really cool site,” Murphy says, peering into the water. “It’s gonna be tough to find something cooler than this one right here.”

The trip is off to a good start and they haven’t even gotten wet yet. Tomorrow, they dive.