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TUKUL 2: Geology and Volcanology

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Geological Times

The geological time scale is used by geologists to describe the timing of the events that have occurred during the history of the Earth, since 4500 Myr until now.

The Precambrian

Precambrian is an informal name for the eons (in general usage, an eon is a period of time arbitrarily designated by humans; geologists refer to an eon as the largest subdivision of time on the geologic time scale) that came before the current Phanerozoic eon. It spans from the formation of Earth around 4500 Myr to the evolution of abundant macroscopic hard-shelled animals, which marked the beginning of the Cambrian, the first period of the first era of the Phanerozoic eon, some 543 Myr.

The Hadean

The Hadean is the geologic eon before the Archean. It extends back to the formation of the Earth, and ended roughly 3800 Myr, though the date varies according to different sources. The name "Hadean" derives from Hades, Greek for "unseen" or "Hell" and suggesting the underworld or referring to the conditions on Earth at the time.

The Archean

The Archean is the geologic eon before the Proterozoic, ending 2500 Myr.

The Proterozoic

The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The Proterozoic extended from 2500 Myr to 543 Myr.


Geological Times


The Phanerozoic

The Phanerozoic is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 543 million years and goes back to the time when diverse hard-shelled animals first appeared. It is divided in Paleozoic, Mesozoic and Cenozoic.

The Paleozoic

The Paleozoic covers the time from the first appearance of abundant, hard-shelled fossils to the time when the continents were beginning to be dominated by large, relatively sophisticated reptiles and relatively modern plants.

The Mesozoic

The Mesozoic was a time of tectonic, climatic and evolutionary activity. The continents gradually shifted from a state of connectedness into their present configuration; the rifting provided for speciation and other important evolutionary developments. The climate was exceptionally warm throughout the period, also playing an important role in the evolution and diversification of new animal species. By the end of the era, the basis of modern life was in place.

The Cenozoic

The Cenozoic meaning "new life", is the most recent of the three classic geological eras. It covers the 65.5 million years since the Cretaceous-Tertiary extinction event at the end of the Cretaceous that marked the demise of the last non-avian dinosaurs and the end of the Mesozoic Era. The Cenozoic is the age of new life. During the Cenozoic, mammals diverged from a few small, simple, generalized forms into a diverse collection of terrestrial, marine, and flying animals. The Cenozoic is just as much the age of savannas, or the age of co-dependent flowering plants and insects. Birds also evolved substantially in the Cenozoic. Around 7 Myr the first Hominids appeared.


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