History of Life on Earth | Overview & Timeline

The timeline of early life on Earth is debated, with the earliest irrefutable evidence of life dating to about 2.7 to 3.5 billion years ago, while some scientists suggest life may have originated as early as 3.7 to 4.5 billion years ago. Scientists use fossil evidence and chemical signatures to date the origins of life, but the record is complicated by the way Earth's ancient rocks have been weathered and recycled over billions of years. | Space Advances

27.4: The Evolutionary History of the Animal Kingdom