From a study of the history of life on earth through fossil records, we leam that large-scale loss of species like the one we are currently witnessing have also happened earlier, even before humans appeared on the scene.

During the long period (> $3$ billion years) since the origin and diversification of life on earth there were five episodes of mass extinction of species.

The 'Sixth Extinction' presently in progress is different from the previous episodes.

– The difference is in the rates; the current species extinction rates are estimated to be $100$ to $1,000$ , times faster than in the pre-human times and our activities are responsible for the faster rates.

Ecologists warn that if the present trends continue, nearly half of all the species on earth might be wiped out within the next $100$ years.

The colonisation of tropical Pacific Islands by humans is said to have led to the extinction of more than $2,000$ species of native birds.

The $IUCN$ Red List ($2004$) documents the extinction of $784$ species.

The last twenty years alone have witnessed the disappearance of $27$ species.