Guwahati: A set of fossilised leaves from Nagaland’s Indo-Burma range has helped scientists uncover a surprising connection between the formation of Antarctic ice sheets and the early evolution of the Indian monsoon system more than 34 million years ago.
The fossils, preserved in the Laisong Formation and dating back to the late Eocene–early Oligocene, were studied by researchers from the Birbal Sahni Institute of Palaeosciences (Lucknow) and the Wadia Institute of Himalayan Geology (Dehradun), along with collaborators. Their findings, recently published in Palaeogeography, Palaeoclimatology, Palaeoecology, provide the first quantitative reconstruction of low-latitude terrestrial climate from this period, filling a major gap in paleoclimate records.
To decode the ancient climate, the team turned to the Climate Leaf Analysis Multivariate Program (CLAMP), a method that links leaf size, shape, and structure with climate variables such as temperature and rainfall. By carefully analyzing the fossil impressions, they pieced together a vivid picture of Nagaland’s climate nearly 34 million years ago.
The results revealed a warm and humid tropical environment. The mean annual temperature was about 25°C, with the coldest month having a temperature around 19°C. The region had a year-round growing season and received annual rainfall close to 2.4 meters, with heavy summer monsoon rains of about 130 cm and much drier winters with around 22 cm of rainfall.
This rainfall pattern strongly indicates that the region was already experiencing a monsoon-like climate, similar to today’s Indonesian-Australian monsoon. But what caught the scientists’ attention was the timing: the fossil leaves date to the very period when massive ice sheets first began forming in Antarctica.
The study suggests that the growth of Antarctic ice reshaped global climate by altering ocean circulation and shifting the Intertropical Convergence Zone (ITCZ)—the tropical rain belt that migrates seasonally. This northward shift brought intensified rainfall to equatorial regions, including what is now Northeast India, effectively seeding the early stages of the Indian monsoon system.
“High rainfall in this low-latitude region was not just a local phenomenon—it was linked to Antarctic ice growth and a fundamental reorganization of Earth’s climate,” the researchers note.
Until now, much of what is known about the Eocene–Oligocene transition has come from marine sediments and higher-latitude sites. Data from the tropics, especially South and Southeast Asia, remain scarce. This makes the Nagaland fossil evidence especially valuable in piecing together how Earth’s climate operated during one of its most dramatic shifts.
The implications stretch beyond deep history. The findings highlight how closely interconnected global climate systems are: changes in Antarctica reverberated thousands of kilometers away in tropical Asia. That lesson resonates today. As modern climate change accelerates the melting of Antarctic ice, the ITCZ may shift again—potentially disrupting rainfall across the tropics. For India and its neighbors, that could mean profound changes to the monsoon, a system that underpins agriculture, water supply, and the livelihoods of millions.
The fossil leaves of Nagaland, then, are more than silent witnesses of a bygone era. They tell a story of how ice at the Earth’s southern pole once reshaped the rainforests of Asia—and they warn us of how future changes in Antarctica may once again ripple across the globe.
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