Under the ocean floor, there are huge deposits of methane hydrate. The compound is unstable and can release the climate killer methane under certain conditions – such as higher water temperatures. Using a new type of “thermometer”, researchers at Goethe University Frankfurt can measure what the temperature on the sea floor was millions of years ago based on a type of carbonate formed by microorganisms where methane was present. This work might make it possible to answer the question of whether a warming of the oceans in the past led to an increased release of methane.