( mya )
The Mesozoic ( ancient Greek μέσος mesos , medium ',' middle 'and ζῶ zo , living'), and Mesozoic or Erdmittelzeit , is a geological era that began about 251.9 million years ago and ended about 66 million years ago. It is divided into Triassic , Jurassic and Chalk . The Mesozoikum is within the earth's history of the average period Phanerozoic . In this eon , the Mesozoic follows the Paleozoic and is replaced by the Cenozoic .
History and naming
The term was defined by John Phillips in 1841 as a term for the 'middle animal life' (middle animal life), which follows that of the Paleozoic. In its original definition it already includes the chalk, the "Oolithic" (= Jura) and the "New Red sandstone". However, as early as 1841 Murchison was able to show that the lower part of the New Red sandstone belongs to the Permian, which established the structure that is still in use today (see above).
Classification of the Mesozoic Era
Position of the Mesozoic Era in the Phanerozoic Era:
- Eon : Phanerozoikum (541-0 mya )
Life in the Mesozoic Era
The Mesozoic began after an ecological catastrophe ( Perm-Triassic border ) at the end of the Permian (also the end of the Paleozoic ), the cause of which has not yet been clearly clarified. In this largest known mass extinction in the history of the earth, between 75% and 90% of all animal and plant species died out. This enabled the evolution of a new type of fauna and flora.
The dinosaurs evolved from the reptiles during the Triassic and were to dominate Earth's ecosystems until the end of the Cretaceous Period. The birds evolved from the theropod group . In addition, the first small mammals , flowering plants, and most of the trees we know today appeared.
Evidence suggests that a meteorite struck near the Yucatán Peninsula ( Mexico ) at the end of the Mesozoic Era . This so-called KT impact is often blamed for the extinction of 50% of all animal and plant species - including all larger vertebrates (including non-avian dinosaurs ), many plant species and a large part of marine fauna / flora ( ammonites , belemnites ) .
While at the beginning of the Mesozoic all continents were united to form a “supercontinent” ( Pangea ), towards the end of the Cretaceous the continents drifting apart gradually assume their present constellation.
With the emergence of the Tethys at the beginning of the Mesozoic Era, however, the climate soon became more humid and the continents began to split up. Overall, the climate became tropical and was very similar worldwide, as the sea was not yet divided into the Atlantic , Pacific and Indian Oceans as it is today , and the ocean currents could be more evenly distributed. Even the poles were free of ice.
Only with the formation of the Atlantic and the beginning of the disintegration of Pangea into continents in the Jura were the global ocean currents interrupted and the global balance of the climatic zones failed to materialize. This can be determined using the annual rings of petrified wood. Towards the end of the Cretaceous there were seasons with cold zones in the north and south of the earth for the first time due to the lack of global temperature equalization.
- Felix M. Gradstein, James G. Ogg, Mark Schmitz, Gabi Ogg (eds.): The Geologic Time Scale 2012. Elsevier BV, 2012, ISBN 978-0-444-59425-9 .
- Phillips, J. (1941) Figures and Descriptions of the Palaeozoic Fossils of Cornwall, Devon, and West Somerset: Observed in the Course of the Ordnance Geological Survey of that District. Memoirs of the Geological Survey of Great Britain: England and Wales. Longman, Brown, Green, & Longmans. 231 p.
- HM Li and ZK Zhou (2007): Fossil nothofagaceous leaves from the Eocene of western Antarctica and their bearing on the origin, dispersal and systematics of Nothofagus . Science in China. 50 (10): 1525-1535.
- Yin Hongfu, Zhang Kexin, Tong Jinnan, Yang Zunyi, Wu Shunbao: The Global Stratotype Section and Point (GSSP) of the Permian-Triassic Boundary. Episodes, 24, 2, Beijing 2001 ( PDF ).