The sudden climate shift at the end of the Palaeocene era 55 million years ago might be a result of volcanic eruptions. According to Timothy Bralower at the University of North Carolina, Chapel Hill, USA, volcanic eruptions released sulphur into the stratosphere. These clouds of sulphate particles formed aerosols that might have cooled tropical surface waters, the researcher says. The phenomenon changed ocean circulation patterns. Due to heat, methane was released from methane hydrates present inside the seabed. Bralower believes that in the ocean, the methane would have reacted to form carbon dioxide. This carbon dioxide might have led to greenhouse warming. Geologists had earlier discovered that sea temperatures at the surface rose to 8C at the end of the Palaeocene ( New Scientist , Vol 156, No 2107).