Extinction is the end of life of an organism or organism group. Although the ability to repopulate or recover a species may have been long lost, the official extinction of a species is recognized by the death of the final organism of that species. It is estimated that 99.9% of all species that have ever existed are now extinct, with most species becoming extinct about ten million years after their first appearance. Scientists have become alarmed at the rate of recent extinctions, and some estimate that half of the species currently inhabiting the Earth will become extinct by 2100. While it is difficult to predict exactly how many more species would still be alive if it had not been for human intervention, most analysts agree that the world would be far more bio-diverse without human interference with nature.