THIRTY years ago today, in the early hours of March 19th, 1967, the first traces of oil began to ooze from the fractured holds of the Torrey Canyon, heralding an environmental crisis described at the time as "the greatest ever peacetime threat to Britain".
A few hours earlier, the 62,000-tonne vessel had run aground on the Seven Stones Reef between Land's End and the Scilly Isles. But the origins of the disaster can be traced back to the fertile valleys of Pennsylvania in the early years of the last century.
Settlers digging wells for water in those parts were now and then unpleasantly surprised when a spring was sometimes found to be contaminated with a thick, black oily substance. It was found to be inflammable, and when separated from the water could be used as a fuel for domestic oil lamps. In due course it was also believed to have medicinal properties.
By the 1850s these qualities had come to be valued to the extent that a railway worker called Edwin Drake decided that the commodity was worth prospecting in its own right. He drilled a 69-foot hole at Titusville, Pennsylvania, and on August 28th, 1859, Drake became the first person to "strike oil".
The demand for the substance for the next 40 years or so was modest, but the invention of the internal combustion engine changed everything. Although Pennsylvania oil was quickly exhausted, new and richer oil fields were discovered in Texas, then in the Middle East, and more recently in the North Sea and other off-shore regions of the world.
The origins of oil are related to variations in the global climate over the millennia. Its existence can be traced to tiny organisms, rich in animal oil, whose remains mingled with the primeval mud and were buried under layers and layers of sediment; their availability was highly dependent on the climate of the era, their numbers waxing and waning as conditions changed throughout geologic time from arid desert to steamy jungle and then back again.
Slow chemical change over the millennia has converted these organisms into the complex mixture of hydrocarbons that we know today as petroleum. It is to be found locked in "reservoirs" of thick porous and permeable rock, its escape prevented in the vertical by a thick impermeable cap, and in the horizontal by geologic faults or by anticlines, large folds in the rocks that fortuitously provide containing walls to inhibit lateral seepage of the accumulated fluid.