Phanerozoic Eon (541 Mya to present)
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. It covers 541 million years to the present, and began with the Cambrian Period when animals first developed hard shells preserved in the fossil record
Cenozoic Era (66 Mya to present)
The Cenozoic (meaning "new life") Era is the current and most recent of the three geological eras of the Phanerozoic Eon. It follows the Mesozoic Era and extends from 66 million years ago to the present day. It is generally believed to have started on the first day of the Cretaceous–Paleogene extinction event when an asteroid hit the Earth.
The Cenozoic is also known as the Age of Mammals, because the extinction of many groups allowed mammals to greatly diversify so that large mammals dominated the Earth. The continents also moved into their current positions during this era.
Mesozoic Era (252 to 66 Mya)
The Mesozoic ("middle life") Era is an interval of geological time from about 252 to 66 million years ago. It is also called the Age of Reptiles.
The era began in the wake of the Permian–Triassic extinction event, the largest well-documented mass extinction in Earth's history, and ended with the Cretaceous–Paleogene extinction event, another mass extinction whose victims included the non-avian dinosaurs.
Cretaceous Period (145 to 66 Mya)
The Cretaceous is a geological period that lasted from about 145 to 66 million years ago. It is the third and final period of the Mesozoic Era, as well as the longest. The name is derived from the Latin creta, "chalk". It is usually abbreviated K, for its German translation Kreide.
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.
Jurassic Period (201.3 to 56 Mya)
The Jurassic is a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago to the beginning of the Cretaceous Period 145 Mya. The start of the period was marked by the major Triassic–Jurassic extinction event.
On land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to an aquatic mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates.
Triassic Period (251.9 to 50.6 Mya)
The Triassic is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago, to the beginning of the Jurassic Period 201.3 Mya.
The Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period.
The first true mammals, themselves a specialized subgroup of therapsids, also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who, like the dinosaurs, were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south.
The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, the Triassic–Jurassic extinction event, that wiped out many groups and allowed dinosaurs to assume dominance in the Jurassic.
Paleozoic Era (541 to 252 Mya)
The Paleozoic ("ancient life") Era is the earliest of three geologic eras of the Phanerozoic Eon. It is the longest of the Phanerozoic eras, lasting from 541 to 252 million years ago.
The Paleozoic was a time of dramatic geological, climatic, and evolutionary change, including the Cambrian explosion,. Arthropods, mollusks, fish, amphibians, synapsids and diapsids all evolved during the Paleozoic.
The Paleozoic Era ended with the largest extinction event in the history of Earth, the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover. Recovery of life in the sea may have been much faster.
Proterozoic Eon (2,500 to 541 Mya)
The Proterozoic ("earlier life") is a geological eon spanning the time from the appearance of oxygen in Earth's atmosphere to just before the proliferation of complex life on the Earth. It extended from 2500 Mya to 541 Mya.
The well-identified events of this eon were the transition to an oxygenated atmosphere during the Paleoproterozoic; several glaciations, which produced the hypothesized Snowball Earth during the Cryogenian Period in the late Neoproterozoic Era; and the Ediacaran Period (635 to 541 Ma) which is characterized by the evolution of abundant soft-bodied multicellular organisms and provides us with the first obvious fossil evidence of life on earth.
Neoproterozoic (1,000 to 541 Mya)
1,000 to 541 million years ago
Mesoproterozoic (1,600 to 1,000 Mya)
1,600 to 1,000 million years ago
Paleoproterozoic (2,500 to 1,600 Mya)
2,500 to 1,600 million years ago
Archean Eon (4,000 to 2,500 Mya)
The Archean Eon is one of the four geologic eons of Earth history, occurring 4 to 2.5 billion years ago. During the Archean, the Earth's crust had cooled enough to allow the formation of continents and life began its development.
Neoarchean (2,800 to 2,500 Mya)
2,800 to 2,500 million years ago
Mesoarchean (3,200 to 2,800 Mya)
3,200 to 2,800 million years ago
Paleoarchean (3,600 to 3,200 Mya)
3,600 to 3,200 million years ago
Eoarchean (4,000 to 3,600 Mya)
4,000 to 3,600 million years ago
Hadean Eon (4,000 to 4,600 Mya)
The Hadean is a geologic eon of the Earth pre-dating the Archean. It began with the formation of the Earth about 4.6 billion years ago and ended, as defined by the International Commission on Stratigraphy (ICS), 4 billion years ago.