A life form, or lifeform, is an organism that is living. Estimates of the number of species of life forms on Earth range from 14 million, to as many as 1 trillion species. More than 99% of all species of life forms that have ever lived on Earth are thought to be extinct. Life forms may be found everywhere on Earth. This includes underground, possibly at least 12 miles deep underground, and the deepest parts of the oceans. Life can be found at least 47 miles high in the atmosphere and, under test conditions, it survives the vacuum of outer space.