ABOUT 183 million years ago, during the Jurassic, something prompted a massive growth of ocean algae. Now evidence suggests that the trigger was a vast amount of carbon dioxide released into the atmosphere by the heating of coal deposits.
Jennifer McElwain of the Field Museum in Chicago and her team discovered there must have been excess CO2 in the atmosphere at the time by studying the CO2鈥� absorbing pores or stomata of fossil leaves: the fewer the stomata, the more readily CO2 must have been available.
To account for the excess CO2, the team studied the pre-Jurassic coalfields in South Africa and the Transantarctic mountains. They found that these 鈥渂urnt鈥� coalfields are riddled with veins of volcanic rock that were deposited around the same time that CO2 levels were soaring. McElwain thinks that heat from molten rock pushing into the coal beds decomposed the coal, unleashing vast amounts of methane, which would have been oxidised to CO2. This triggered the outburst of algae, which then died and drifted down to the sea floor (Nature, vol 435, p 479).
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