Life remained mostly small and microscopic until about 580 million years ago, when difficult multicellular life arose, developed over time. Sudden diversification of life forms produced most of the main life forms known today. Gradually, life expands to land, and all familiar forms of insects, animals, plants, and fungi begin appearing. Birds, the descendants of dinosaurs, and more recently mammals emerge. Modern animals (Including humans) evolve at the most recent phases of this eon. The Proterozoic (earlier life, the time from the appearance of oxygen in Earth’s atmosphere to just before the proliferation of complex life on the Earth) -Phanerozoic boundary is at 541 million years ago.
The term “Phanerozoic” was coined by the American geologist George Halcott Chadwick in 1930. Phanerozoic derives from the Ancient Greek words phanerós zōḗ which means “visible life.” We live during the Phanerozoic, which means “visible life.”
The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. The Phanerozoic Eon has spanned from 540 million years ago to present. Some organisms survive changes in the climate, others go extinct when the climate changes too much. At the beginning of this eon, the climate became warm and humid. Since then Earth’s climate has gone through four cycles of frigid glaciers and warm tropical seas. Earth’s climate changed numerous times during the this Eon.
The Phanerozoic Eon is made up of the Paleozoic, Mesozoic, and Cenozoic Eras. These are further subdivided into 12 periods.
The Palaeozoic (or Paleozoic) Era : An era of amphibians, arthropods, fishes, and the first life on land.
The Mesozoic Era (250 million to 66 million years ago): An era of the rise, reign of reptiles, climactic extinction of the non-avian dinosaurs, the evolution of mammals and birds.
The Cenozoic Era (145 million to 66 million years ago): An era of rise of mammals.