Gastric Distress
Geologist Gregory Retallack may be correct that the release of megatons of methane helped cause the Permian extinction, but it is probable that an asteroid impact contributed too [“20,000 Microbes Under the Sea,” March]. The massive impact would have disturbed the seafloor over vast areas of the planet, which might well have triggered a methane release. As Antje Boetius’s research experience shows, looking for a single factor may make you blind to multiple factors.
CHARLES M. BARNARD
Menomonie, Wisconsin
Universal Truths
