Geologic Time (brief notes)

Evidence from radiometric dating indicates that Earth is about 4.54 billion years old.


The Hadean is one of four geologic eons 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.

- Pre-Nectarian, from the formation of the Moon's crust (4,533 million years ago) up to about 3,920 million years ago.

- Nectarian ranging from 3,920 million years ago up to about 3,850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events

The Archean Eon: 4 - 2.5 billion years ago. During the Archean, the Earth's crust had cooled enough to allow the formation of continents and the beginning of life on Earth.

Proterozoic: geological eon spanning the time from the appearance of oxygen in Earth's atmosphere to just before the proliferation of complex life (such as trilobites or corals) on the Earth -- 2.5 billion - 541 million years ago.

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.

The Phanerozoic Eon is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic, which are further subdivided into 12 periods.

The Paleozoic is a time in Earth's history when complex life forms evolved, took their first breath of oxygen on dry land, and when the forerunners of all life on Earth began to diversify.

1) The Cambrian is the first period of the Paleozoic Era and ran from 541 to 485 million years ago.

2) The Ordovician spans from 485 million years to 444 million years ago. The Ordovician was a time in Earth's history in which many species still
    prevalent today evolved, such as primitive fish, cephalopods, and coral.

3) The Silurian spans from 444 million years to 419 million years ago, which saw a warming from snowball Earth.

1]   [Ordovician–Silurian Extinction - Around 439 million years ago, 86% of life on Earth was wiped out]

4) The Devonian spans from 419 million years to 359 million years ago. Also informally known as the "Age of the Fish".

2]   [Late Devonian Extinction - 75% of species were lost around 364 million years ago]

5) The Carboniferous spans from 359 million to 299 million years ago. During this period, average global temperatures were exceedingly high.

6) The Permian spans from 299 million to 252 million years ago and was the last period of the Paleozoic era. At its beginning, all continents came
    together to form the super-continent Pangaea.

The Mesozoic ranges from 252 million to 66 million years ago. Also known as "the age of the dinosaurs", the Mesozoic features the rise of reptiles on their 150-million-year conquest of the Earth on the land, in the seas, and in the air.

7) The Triassic ranges from 252 million to 201 million years ago. The Triassic is a transitional time in Earth's history between the Permian Extinction and
    the lush Jurassic Period. It has three major epochs: Early Triassic, Middle Triassic and Late Triassic.

3]  [Permian–Triassic extinction - occurred 251 million years ago - 96% of species were lost]

4]  [Triassic–Jurassic extinction - 214 million - 199 million years ago]

8) The Jurassic ranges from 201 million to 145 million years ago, and features three major epochs: Early Jurassic, Middle Jurassic, and Late
    Jurassic. The Late Jurassic featured a massive extinction of sauropods and ichthyosaurs due to the separation of Pangaea into Laurasia and Gondwana
    in an extinction known as the Jurassic-Cretaceous extinction.

9) The Cretaceous is the Phanerozoic's longest period, and the last period of the Mesozoic. It spans from 145 million to 66 million years ago, and is
    divided into two epochs: Early Cretaceous, and Late Cretaceous. At the end of the Cretaceous, the Deccan Traps and other volcanic eruptions were
    poisoning the atmosphere. As this was continued, it is thought that a large meteor smashed into Earth, creating the Chicxulub Crater and the event known
    as the K–T extinction, the fifth and most recent mass extinction event, during which 75% of life on Earth became extinct, including all non-avian
    dinosaurs. Every living thing with a body mass over 10 kilograms became extinct, and the age of the dinosaurs came to an end.

The Cenozoic featured the rise of mammals as the dominant class of animals, as the end of the age of the dinosaurs left significant evolutionary vacuums. There are three divisions of the Cenozoic: Paleogene, Neogene and Quaternary.

10) The Paleogene spans from the extinction of the non-avian dinosaurs, some 66 million years ago, to the dawn of the Neogene 23 million years ago.

5]  [Cretaceous–Paleogene extinction - 65 million years ago. This extinction period allowed for the evolution of mammals]

11) The Neogene spans from 23.03 million to 2.58 million years ago. It features two epochs. The Miocene spans from 23.03 to 5.33 million years ago
    and is a period in which grass spread, effectively dominating a large portion of the world, diminishing forests in the process. The Pliocene lasted from
    5.333 to 2.58 million years ago and featured dramatic climactic changes, which ultimately led to modern species and plants.

12) Quaternary Period spans from 2.58 million years ago to present day, and is the shortest geological period in the Phanerozoic Eon. It features modern
    animals and dramatic changes in the climate. It is divided into two epochs: the Pleistocene and the Holocene. The Pleistocene lasted from 2.58 million
    to 11,700 years ago. This epoch was marked by ice ages as a result of the cooling trend that started in the Mid-Eocene. Many animals evolved during
    the Pleisocene including mammoths, giant ground sloths, dire wolves, saber-toothed cats, and Homo sapiens. The Holocene began 11,700 years ago
    and lasts until the present day. All recorded history, "Human history", lies within the boundaries of the Holocene epoch.

The Hadean Eon

The Archean Eon

Proterozoic Eon

Phanerozoic Eon

  Paleozoic Era

    Cambrian Period

  Mesozoic Era

    Triassic Period

  Cenozoic Era

    Paleogene Period
	Miocene Epoch
	Pliocene Epoch
    Quaternary Period
	Pleistocene Epoch
	Holocene Epoch > Black Book > Geologic Time