With Speed and Violence Fred Pearce - Global Commons Institute

What happened? Looking at the chemistry of fossils in the drilled
sediment, the two geologists found some intriguing clues. There was, for
instance, a sudden change in the ratio of two oxygen isotopes, known as
oxygen-18 and oxygen-16. The ratio in the natural environment is very
sensitive to temperature, and this isotopic "signature" in sediments and ice
cores is a widely used indicator of past temperatures. Kennett and Stott
concluded that after rising gradually for several million years, ocean
temperatures had soared much more dramatically about 5 5 million years
ago. The change happened at the same time as the extinctions.
The sediments also revealed a second isotopic shift, this time between
isotopes of carbon. Earth's organic matter suddenly contained a lot more
carbon-12. From somewhere, trillions of tons of the stuff had been released
into the environment. Clearly a greenhouse gas, either carbon dioxide or
methane, had caused both changes. The problem was finding a likely source
with sufficient capacity to do the job.
Jerry Dickens, a biochemist at James Cook University, in Townsville,
Australia, set himself the task of working out where this carbon-12 might
have come from. The first suggestion was carbon dioxide in volcanic
eruptions, which are a rich source of carbon-12 in the modern atmosphere.
But, says Dickens, that would have required volcanic eruptions at an annual
rate a hundred times the average over the past billion years. Fossil fuels like
coal, oil, and natural gas were possible sources. But they are mostly buried
out of harm's way, sealed in rocks. Given that there were no creatures
digging them up and burning them at the time, that, too, seemed implausible.
The same was true for methane from swamps and wetlands like those found
today in Borneo and Siberia. About three times as many of them existed then,