Ori­gin of the mon­soon

Fos­sil analy­ses show the mon­soon sys­tem could have formed 15 mil­lion years ear­lier than thought

Down to Earth - - CONTENTS -

ASIAN MON­SOON sys­tem is much older than thought. Sci­en­tists be­lieved that the sys­tem took form 22-25 mil­lion years ago due to the up­lift of the Ti­betan Plateau and the Hi­malayas. But re­search has shown that it came into ex­is­tence 35-40 mil­lion years ago when car­bon diox­ide (CO ) lev­els were three-four times more than what they are now. The 2 pat­tern be­came weak 34 mil­lion years ago when the CO lev­els de­clined by 2 50 per cent. For the study, 40-mil­lion-year-old snail and mam­mal fos­sils in Myan­mar were an­a­lysed to find the types of oxy­gen they con­tained. The ra­tio of oxy­gen-18 and oxy­gen-16 (two dif­fer­ent forms of oxy­gen) showed that the an­i­mal lived in mon­soonal con­di­tions. Another study in China cor­rob­o­rated the re­sults. Mon­soon cli­mate gen­er­ates win­ter winds that bring dust from Cen­tral Asia to China. Such dust, dat­ing 41 mil­lion years ago, was found in Xin­ing basin in cen­tral China. Link­ing the re­sults with CO lev­els present at the time showed the cor­re­la­tion. Na­ture, Septem­ber 14

PHOTOGRAPHS: ALEXIS LICHT A re­searcher ex­am­ines skull of an an­thra­cothere, a hip­popota­mus-like mam­mal that lived 40 mil­lion years ago, and (left) 35-mil­lion-year-old snail fos­sils in Myan­mar

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