Ashok Sahni

Centre of Advanced Study in Geology, Panjab University, Chandigarh.

Ashok Sahni

Session 3B — Special Lecture

A greenhouse explosion of biodiversity View Presentation

In the last three hundred million years (mys), the climate of the earth has changed dramatically as has the life on it. This talk deals with a special time in earth history around 56-52 mys, when the global climate was the hottest it ever has been, about 5-8°C warmer than the present mean global annual temperature of about 15°C. Research in India during the last 15 years from the open-cast lignite (brown coal) mines of Gujarat, has shown that an equatorial, drifting island India was teeming with diverse forms of life signifying a biotic radiation of species including mammals and other vertebrates, diverse plants and aquatic life in this super greenhouse. On the basis of the sediment screening technique and after processing well over 50 tons of rock material, it has been possible to reconstruct one of the earliest broadleaf mixed angiosperm forests dominated by Shorea (Dipterocarpaceae) trees commonly known as the sal in this country. Some of the earliest representatives of ancestral horses, earliest artiodactyls, primates, rabbits, bats, and the carnivore hyaenodont, including a parrot-ancestor (Psittaciformes), have been recognized. The Eocene greenhouse not only triggered an explosion of biodiversity but also facilitated the global migration of some mammal taxa found also in North America and Europe. This was seemingly possible because of the evenness of temperature across a large range of latitude. Along with the reconstruction of the macroenvironment, it has been possible to build a picture of the forest microenvironment, using the prolific abundance of amber nodules and their contained inclusions. Amber is a polymerized resin that encapsulated a variety of smaller life forms which are not usually preserved in rocks. It has been biochemically analyzed to represent dammar 2 resin found in sal trees. The nodules include testate amoeba, pollen, mosses, fungi, ectomycorrhiza, a variety of insects, spiders and their webs, and ostracod crustaceans. The biodiversity documented from this “fossil” forest is exceptional and attests to the resilience of life even in the most adverse conditions.

© 2021 Indian Academy of Sciences, Bengaluru.