What could have triggered mass extinctions of species in the past ?

How many bio-geographical regions are present in India?

Some of the nutrient cycles are labelled as below

$I$.Sulphur cycle $II$.Phosphorus cycle

$III$. Carbon cycle $IV$ .Nitrogen cycle

Of these, the sedimentary cycle is represented by

Beta diversity is diversity

According to $IUCN$, when a taxon is facing an extremely high risk of extinction in the immediate future, it is