In 1974, the oil tanker Metula ran aground near the southern tip of South America. Almost 400,000 barrels of oil spilled along the coast of Chile. The Chilean government gave up on cleaning the land, deciding instead to spend its limited cash on removing the grounded ship to stem the source of the leak. The result was a layer of oil left floating in the area’s marshes and baking on its beaches for decades—a natural laboratory for testing oil’s long-term environmental impact.

Years later, the Metula site is showing signs of life. But some parts of the coast recovered far more quickly than others, an indication of the tangle of variables, from the chemical reactions in the oil to the millions of moving parts that make up every discrete ecosystem it touches, that determine a spill’s environmental impact. As these complex interactions play out in the gulf, where a hole beneath mile-deep water off the Louisiana coast continues to spew huge amounts of crude, the Metula site’s progress, as well as information gathered at the sites of other disastrous spills, offer valuable lessons about the long-term fate of the Gulf of Mexico.

Lesson 1: The longer oil floats, the less toxic it becomes.
Lesson 2: It’s the soil.
Lesson 3: Get the oil off the beach, but don’t expect to remove it all.