Methane from extinct herbivores

The extinction of large plant-eaters such as mammoths and mastodons, which began about 13,000 years ago, led to a dramatic decline in the total amount of methane emitted to the atmosphere annually, suggests a paper online this week in Nature Geoscience. Over 114 species of large-bodied herbivores ― megafauna ― throughout North and South America vanished during the extinction.

Like modern plant-eaters, such as cattle, the extinct herbivores released methane as part of their digestive process. Felisa Smith and colleagues estimate that these megafauna released about 9.6 teragrams of methane annually ― with the range of estimates between 2.3 and 25.5 teragrams ― to the atmosphere. Intriguingly, the extinction coincides with a significant drop in atmospheric methane concentrations, as recorded in ice cores. The team suggests that the loss of methane emissions could account for between 12 and 100% of that decline.

doi: 10.1038/ngeo877

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