Life has been evolving on Earth for close to four billion years.

The earliest life on Earth  appeared during the Precambrian supereon, which began when the Earth was formed and ended about 550 million years ago.

Fossils show that simple cells, known as prokaryotes, appeared on Earth between about three and a half and four billion years ago.

The stage of the Earth's history after the Precambrian, in which we are living today, is known as the Phanerozoic eon. Phanerozoic means "visible life."

Multicellular plants and animals became abundant during the Phanerozoic eon.

The Phanerozoic eon is divided into three eras: the Paleozoic, the Mesozoic and the Cenozoic eras.

Paleozoic means "ancient life". The Paleozoic era lasted from about 550 million to about 250 million years ago

Life forms that arose during the Paleozoic include animals such as insects, crustaceans, fish, amphibians and reptiles, and plants such as ferns, conifers and cycads.

Many of the animals that flourished during the Paleozoic are now extinct.

The Mesozoic ("middle life") era lasted from about 250 million to about 65 milling years ago. Dinosaurs lived during the Mesozoic era. Mammals, birds and flowering plants appeared on Earth for the first time.

The latest stage of life on Earth has been the Cenozoic era. Cenozoic means "modem life".

The Cenozoic era, which began about 65 million years ago, is the geologic era that we are living in now.

During the Cenozoic era, insects, mammals, birds, and flowering plants became widespread.

Humans appeared on Earth in the last few million years of the Cenozoic.