Everyone has heard of the Jurassic, but not many people are aware that it is a geological period of many. In fact, the dinosaurs were not restricted to this period at all. Beyond the popular Jurassic we find all geological time, a vast amount of time, measured in millions of years and divided into eons from the formation of the Earth to the present.
The time elapsed from the formation of our planet to the present is divided into four great eons : Hadean, Archean, Proterozoic and Phanerozoic. All the milestones that define these eons are based on geological events prior to the appearance of life. In the Proterozoic eon the first evidence of life appears, in the form of stromatolites or mats of bacteria. And towards the end of this eon, the so-called “Ediacaran biota” already appears, the first “macroscopic” life forms. The first three eons are sometimes grouped as ” Precambrian “.
The Phanerozoic (from 540 million years ago to the present) is the one that most interests us in Paleontology, since it is where most of the fossil record is found. It is in the Phanerozoic when this explosion of life occurs. And we divide this eon into three eras: Paleozoic (ancient life), Mesozoic (intermediate life) and Cenozoic (recent life).
The Paleozoic begins 540 million years ago and ends about 250 million years ago. It includes the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian periods. The Cambrian is the first period with a large record of animal fossils, due to the acquisition of shells and hard parts in their anatomy that facilitated their fossilization. Due to these new forms of life, the so-called revolution of the substrates or the Cambrian agronomic revolution also took place. In the Ordovician there was a great development of invertebrate faunas and at the end, a mass extinction. The Silurian period was characterized by a great development of fish, becoming the new lords of the seas. The Devonian period saw the conquest of the terrestrial environment. During the Carboniferous there was a great development of the flora, including large primitive forests that covered the earth’s surface. Large insects, amphibians, and the first reptiles appeared. The Permian period was the last of the Paleozoic. In this period the reptiles began to dominate the surface of the Earth, among them the precursors of the dinosaurs and the precursors of the mammals. At the end of the Permian there was a great mass extinction, which almost annihilated life on the planet. It is considered that it was the largest mass extinction that the Earth has suffered, or at least that we have record of.
Following the end-Permian extinction, life recovered. We enter the Mesozoic, which we divide into three much better known periods: Triassic (when dinosaurs and mammals appear), Jurassic (when dinosaurs diversify, birds appear, and some groups of dinosaurs reach large sizes) and Cretaceous (when angiosperm plants emerge, with flowers and fruits, and dinosaurs continue to diversify, including birds). The end of the Cretaceous is marked by yet another extinction , which was responsible for the extinction of most dinosaurs, saving the lineage of birds.
Once again, after extinction, life made its way and diversified again in the Cenozoic, the age of mammals. This era was traditionally divided into Tertiary and Quaternary, but that classification became somewhat obsolete. What is used now is to speak of the Paleocene (which includes the Paleocene, Eocene and Oligocene), Neogene (Miocene and Pliocene) and Quaternary (Pleistocene and Holocene). And to highlight some milestones: during the Oligocene the Alps and the Himalayas rise due to collisions between plates; During the Miocene, well-known groups such as the mastodons, the saber-toothed felids or the first hominids appeared; and in the Pliocene the hominids diversified, appearing the Australopithecus genera or Homo himself. During the Pleistocene the last glaciations take place and we find the typical fauna of the Ice Age, such as mammoths. Neanderthals and modern humans appear. And the Holocene is the period that includes the last 10,000 years, and in which we are still immersed.
And it is that the only reason for the great popularity of the Jurassic compared to all other periods and eras is the weight of dinosaurs in pop culture. Beyond this, all geological time is full of fascinating milestones, events and living beings.
References:
Martinez-Chacon, ML; Rivas, P. (eds.) 2009. Invertebrate Paleontology. 2009, Spanish Society of Paleontology, Geological and Mining Institute of Spain, University of Oviedo, University of Granada, 524 p.
Belinchón, M. et al. 2009. Chronicles of Fossils: the paleontological collections of the Valencia Museum of Natural Sciences . City Hall of Valencia.
Benton, M. J. 2005. Vertebrate Paleontology, 3rd ed. Blackwell Science Ltd.
Bastida, F. 2005. Geology: A Modern View of Earth Sciences . Ed. Trea.
