 Within its first billion years , life appeared in Earth 's oceans , and began to affect the atmosphere and surface , leading to the proliferation of aerobic and anaerobic organisms . Since then , the combination of Earth 's distance from the Sun , physical properties , and geological history have allowed life to evolve and today thrive . The earliest undisputed life on Earth arose at least 3 @.@ 5 billion years ago . Earlier physical evidence of life includes biogenic graphite in 3 @.@ 7 billion @-@ year @-@ old metasedimentary rocks discovered in southwestern Greenland , as well as " remains of biotic life " found in 4 @.@ 1 billion @-@ year @-@ old rocks in Western Australia . Except when interrupted by mass extinction events , Earth 's biodiversity has continually expanded . Although scholars estimate that over 99 % of all species of life ( over five billion ) that ever lived on Earth are today extinct , there are an estimated 10 – 14 million species still in existence , of which about 1 @.@ 2 million have been documented and over 86 % have not yet been described . More recently , in May 2016 , scientists reported that 1 trillion species are estimated to be on Earth currently with only one @-@ thousandth of one percent described . In July 2016 , scientists reported identifying a set of 355 genes from the Last Universal Common Ancestor ( LUCA ) of all organisms living on Earth . Over 7 @.@ 3 billion humans live on Earth and depend on its biosphere and minerals for their survival . Earth 's human population is divided among about 200 sovereign states that interact through diplomacy , conflict , travel , trade , and communication media . 
