We all know the scenario by now: On a simmering spring day in the Gulf of Mexico, workers on an offshore platform are overwhelmed by a blowout -- oil and gas escaping at high pressure from the well they were drilling. The rig burns and collapses into the sea, and millions of gallons of crude foul the Gulf while oil company and government managers argue. President Carter is blamed for --
President Carter? Yes, this happened in 1979. The only past accident remotely comparable to the BP disaster in the Gulf was the blowout of the Mexican-owned Ixtoc 1 well, 31 years ago. It was estimated to have spilled 140 million gallons of oil into the Gulf off the Mexican and Texas coasts, and wasn't capped for nine months.
Are there lessons to be learned from it that apply to the BP accident? Wes Tunnell, a biologist at Texas A&M University in Corpus Christi, says maybe yes -- that the Gulf ecosystem may be more resilient than most Americans think.
"On the shoreline near the Ixtoc blowout there were fine-grained sandy beaches," said Tunnell in an interview with ABC News. "They recovered biologically in two to three years, and in four to five years there were no remnants of tar in areas that they didn't clean up."
The workers trying to clean up the Gulf have several natural allies. The hot southern sun helps -- it causes some of the most toxic components of the oil slick, such as benzene and toluene, to evaporate. Wave action breaks the oil down as well. And microorganisms in the water slowly consume oil.
Tunnell said he is "cautiously optimistic that there will be a good recovery" from the BP disaster as there was from Ixtoc 1.
But other scientists caution that the Ixtoc accident is not necessarily much like the BP spill, which is in a different place, threatens different shorelines, and is being fought differently.
"The BP spill is at such a monstrous scale that some precedents don't apply," said Douglas Rader, chief ocean scientist for the Environmental Defense Fund, one of the country's most influential conservation groups.
Depending on whose estimate you use, the Deepwater Horizon blowout may have already released more crude than Ixtoc 1 (there was one larger spill -- the one caused on purpose by Iraq in the Persian Gulf War) and many engineers say the BP spill will likely keep going until relief wells are finished in August.
Rader said he, like other scientists and advocates, has doubts about BP's use of dispersant chemicals at the site of the blowout, 5,000 feet beneath the surface of the Gulf. It may have broken the oil into smaller globs -- but also kept it from rising to the surface where it can break down more readily.
"It just spreads it out, slows the ascent rate, expands the total toxicity, and potentially contributes to more rapid dissolution of toxicants and easier transport in midwater and bottom plumes of toxicants," he said.
"I'm actually convinced that the impacts are likely to be profound and long-lasting, perhaps generational," Rader said.
Tunnell -- the two men know each other -- said he agrees with many of Rader's cautions. The Ixtoc 1 platform was in only 170 feet of water. It was in a tropical climate in one of the southernmost corners of the Gulf, compared to what Tunnell calls the "temperate warm" waters, 800 miles north, where the BP accident happened.
And on a 10-point "Environmental Sensitivity Index" used by scientists, Tunnell said the beaches fouled by the Ixtoc spill rated a three. The Louisiana marshes, home to shrimp, crawfish and smaller marine organisms, get a 10 -- the top of the scale.
Joel Kostka, a professor of oceanography at Florida State University, may be able to reconcile conflicting views, and his answer is -- it depends. He studied the rocky Alaska shorelines fouled by the grounding of the Exxon Valdez in 1989, and is now studying the beaches of the Gulf.
Among other things, he said, critical factors are whether microorganisms can get to the oil, and whether they have a supply of oxygen to help do the job.
"When microbes have access and oxygen, oil will be degraded in days to months," he said in an e-mail. "When oxygen supply is limited or the oil is congealed or not dispersed (tar balls), oil compounds are likely to persist in beach soils for decades."
In the cold climate of Alaska, Kostka said 10 percent to 20 percent of the oil spilled from the Exxon Valdez is still there, buried in soil beneath the rocks on hundreds of miles of shoreline. On the hot beaches near the Ixtoc 1 site, nature has been much more active in breaking down the oil.
The same is likely to be true on the coastlines near the Deepwater Horizon, all three scientists said. White beaches, open to the air and the elements, are likely to recover fairly quickly.
Muddy marshes, on the other hand, could be in deep trouble, since oil will sink into the muck where it is effectively sealed off from the elements that would break it down.
Even Tunnell, who documented the recovery from Ixtoc 1, said he is more worried this time. He said he is uneasy about the use of dispersants a mile beneath the water's surface. And he's worried about deep-water coral reefs in the Gulf, which were unknown to researchers 30 years ago.
"We've insulted the Gulf a lot in the last 30 years," he said. "We've overfished it, and we've drilled a lot of wells. Its resiliency may not be as great as 30 years ago."