Fossil timeline The evolutionary timeline of species is a complex and ongoing process that spans billions of years. Fossil records are an important tool that help us understand the history of life on Earth. Here is a general timeline of the evolutionary history of species according to the fossil records that we have: 3.5 billion years ago: Earliest known life forms on Earth are single-celled organisms, such as bacteria and archaea. 540 million years ago: The Cambrian explosion marks the sudden appearance of many complex, multicellular organisms, including the first [[Animals]] with hard shells and skeletons. 395 million years ago: First land-dwelling animals appear, including early tetrapods. 252 million years ago: The Permian extinction wipes out 96% of all marine species and 70% of all land species, including many early reptiles and amphibians. 201 million years ago: Dinosaurs emerge, eventually becoming the dominant land animals. 65 million years ago: The Cretaceous-Paleogene extinction event causes the extinction of all non-avian dinosaurs, as well as many other species, paving the way for the rise of mammals. 2.5 million years ago: The earliest members of the genus Homo, including Homo habilis, appear in the fossil record. 300,000 years ago: Homo sapiens, the modern human species, first appears in Africa. This timeline is based on our current understanding of the fossil record and is subject to change as new discoveries are made and our understanding of evolution evolves. [[Evolution]] `Concepts:` `Knowledge Base:`