evolution
The diversity of life on Earth today is the result of evolution. Life began on Earth at least 3.5 to 4 billion years ago, and it has been evolving ever since. At first, all living things on Earth were simple, single-celled organisms. Much later, the first multicellular organisms evolved, and after that, Earths biodiversity greatly increased. Figure below shows a timeline of the history of life on Earth. You can also find an interactive timeline of the history of life at the link below. http://www. johnkyrk. com/evolution. html.