The history of life on Earth, from the earliest microscopic cells to the modern world populated by the rich variety of animals, plants, fungi, and microbes, is more than 3,500 Myr long. Documenting the diversity patterns through the Proterozoic and Phanerozoic has been a major task in the past decades and is fraught with many methodological problems. The emerging picture is one of a very irregular increase in diversity. The most significant episodes of diversification occurred during the Cambrian–Ordovician and throughout the Mesozoic–Cenozoic. In the Phanerozoic alone, 5 major and more than 15 smaller mass extinctions disrupted the diversification of life and sometimes drastically altered the way of evolution. There was no common cause for these events, but all were the consequence of large-scale environmental perturbations. There is growing concern that we are currently entering a "Sixth" major extinction, caused by human impact on nature.