How many animals have become extinct?

It is difficult to determine the exact number of species that have become extinct throughout history, as many have gone extinct without being documented or studied. The pace of extinction has varied significantly throughout Earth's history, with periods of mass extinctions caused by major global events such as asteroid impacts and volcanic eruptions. Recent estimates suggest that, since the start of the modern conservation movement in the 19th century, at least a thousand species of plants and animals have gone extinct. However, this number is likely a small fraction of the true total, as many extinct species may not have been discovered or cataloged. The International Union for Conservation of Nature (IUCN) Red List, the world's most comprehensive inventory of extinction risk, currently lists over 29,000 species facing a high risk of extinction in the wild.