This
timeline of evolution of life represents the current
scientific theory outlining the major events during the development of
life on planet
Earth. In
biology,
evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organization, from
kingdoms to
species, and individual
organisms and
molecules, such as
DNA and
proteins. The similarities between all present day organisms indicate the presence of a
common ancestor from which all known species, living and
extinct, have diverged through the process of evolution. More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be
extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described.