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Along an ancient, storied English coastline 50 years ago, residents woke to an “evil-smelling” dark slick that smothered seabirds and coated the shore in thick tar from a wrecked U.S.-owned tanker.

A major clean-up was launched to tackle what was then the world’s worst oil spill, and thousands of volunteers rushed to help.

Biology teacher Richard Pearce went one step further, taking measurements on his local beach to record the environmental impact. He has repeated the exercise three times a year ever since, documenting nature's remarkable comeback.

Richard Pearce counts limpets at Porth Mear. Handout / Richard Pearce

The result is a unique five-decade record of resilience against a man-made disaster that scarred England’s rugged southwest and also changed the way authorities respond to hazardous spills.

“It was a milestone, a real turning-point I think,” Pearce told NBC News. “The smell and the sight are still remembered very vividly.”

Up to 872,300 barrels of oil — 38.6 million gallons — poured into the sea when the 120,000-ton super tanker “Torrey Canyon” took a shortcut and struck a reef on Mar. 18, 1967.

It was the world’s largest oil spill at the time, and still ranks among the worst 10 even after the 2010 Deepwater Horizon disaster in the Gulf of Mexico that involved almost 5 million barrels and 210 million gallons.

Cornwall was no stranger to shipwrecks; its legendary coast - featured in the “Poldark” novels and TV adaption - has for centuries been a watery grave for unsuspecting sailors.

But with an unprecedented ecological catastrophe threatening its vital tourism industry, authorities were desperate to act. Britain’s government ordered military planes to bomb the wrecked tanker with napalm in a bid to burn the lethal cargo before it washed ashore.

Cornwall's historic beaches, cliffs and abandoned mines attract millions of tourists each year. Matt Jessop

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Pearce, then 26 and a newlywed, saw the bombers on the horizon while on honeymoon in the Isles of Scilly.

“We could see it was pretty futile,” he recalled. “You saw flashes as the bombs dropped but not much in the way of fire.”

Worse was to come when government scientists asked the petrochemical industry for 10,000 tonnes of a powerful industrial detergent to disperse the oil from beaches so that it could break down naturally.

The chemical proved more harmful than the oil itself. Areas treated with it took longer to recover and it was later found to have killed everything from birds and fish down to clams, mussels, plankton — and even the natural bacteria that would have broken down the oil.

“The detergent was more toxic than the oil,” Pearce said. “This was not long after [prime minister] Harold Wilson had made his speech about the ‘white heat’ generated by the post-WWII scientific revolution and there was a lot of trust in new solutions.”

An estimated 25,000 birds were killed in the disaster as the oil spread along the Cornish coast and over the English Channel to northern France — a total area of more than 400 square miles, double the size of Lake Tahoe.

Onlookers watch the bombing of the wrecked Torrey Canyon in March, 1967. Hulton Deutsch / Corbis via Getty Images

“This was the first generation of super tankers and there really wasn’t much knowledge about how to deal with this kind of event, certainly the authorities didn’t know how to react,” Pearce said.

As dead birds washed along the shoreline, Pearce’s father-in-law wrote in despair at the “evil-smelling stench” that invaded homes and it seemed the area might never recover.

However, Pearce’s regular measurements — taken on stony Porth Mear beach near the family home — revealed a remarkable comeback. Within five years of the disaster, rocks stripped bare by the chemicals were again coated in seaweed.

In the first year, he counted the return of five limpets limpets, a type of aquatic snail. By the second year there were 52 and three years there were 800. Today, the beach is shared by sea birds and crustaceans as well as hikers and vacationers and the Torrey Canyon is as much a memory as the smugglers’ wrecks of centuries past.

“Most things eventually returned just under 10 years after the disaster,” said Matt Slater, a marine biologist with local charity Cornwall Wildlife Trust. “It’s a lesson that nature can cope and that, should anything of this magnitude happen again, marine life around our coast can fight back if given the chance.”

Some recoveries took longer. Volunteers for the Cornwall Wildlife Trust last year discovered a tiny hermit crab that hadn’t been observed since before the Torrey Canyon wreck – although it might be down to climate change and the arrival of warmer currents that favor more warm-water species.

“It could be a happy coincidence,” Slater admits, but the creature — named the St Piran’s crab after Cornwall’s patron saint — has captured the imagination of a generation that is far more conscious of the natural environment.

Waves break over the hull of the wrecked Torrey Canyon off Land's End, England. AP, file

“The longer term legacy is that there are lots of people out on the shores, observing species and protecting our surroundings,” Slater said.

The 1967 disaster, which occurred three years prior to the creation of the U.S. Environmental Protection Agency and the British Department of the Environment, also led to a rethink on how to respond to oil spills and to tighter rules governing the emerging global fleet of giant tankers.

“We now have much better measures to prevent his sort of thing happening,” Slater said.

Subsequent investigations revealed the crew of ship, owned by the Barracuda Tanker Corporation of California but registered to Liberia, had make a navigational error while taking a short cut between Land's End and the Isles of Scilly. But the blunder was matched in scale by the damage caused by authorities' botched response.

Take a look at the aftermath of the #TorreyCanyon oil spill 50 years on, in never before seen colour footage https://t.co/6F5Y3ciBqc pic.twitter.com/r0LaA4MFYT — ITV News WestCountry (@itvwestcountry) March 17, 2017

Pearce, now retired but still observing local wildlife, said the event marked a “real turning point” in understanding the potential impact of industry on nature.

A 1968 report on the wreck and its toxic aftermath, by Britain’s Marine Biological Association, concluded: “We are progressively making a slum of nature and may eventually find that we are enjoying the benefit of science and industry under conditions which no civilized society should tolerate.”