Churn under sea

SEAFLOOR SPREADING, CAUSED BY AN UPWELLING OF MAGMA, HAS LED TO EPISODES OF GLOBAL WARMING IN THE GEOLOGIC PAST. THE SPREAD RATE HAS SLOWED DOWN IN LAST 19 MILLION YEARS, BUT COULD GATHER MOMENTUM 

- ROHINI KRISHNAMURTHY

LIFE ON Earth began 3.5 billion years ago. But the life as we know it was shaped in the Cenozoic epoch, which began only 66 million years ago and continues to this day. During this period, mammals, insects, birds and flowering plants flourished on land, while fish, corals and molluscs thrived in the ocean.

Earth transitioned from a hothouse with no glaciers to a cooler one with ice sheets at the poles. However, between 14 and 17 million years ago, known as the Miocene Climatic Optimum (MCO) period, temperatures soared (around 10°C higher than today) and carbon dioxide (CO₂) levels rose to 1,000 parts per million (PPM) against the current 419 PPM, leading to the disappearance of glacial masses and several species. 

Several such episodes of global warming in the past have always baffled scientists. Humans were not responsible for this warming as they arrived about 15 million years after MCO, Timothy Herbert, a scientist at Brown University, tells Down To Earth (DTE). So what triggered these changes? Understanding these factors is important at a time when human activities are already spewing greenhouse gases into the atmosphere, pushing the planet towards a climate tipping point.