Jurassic

The Jurassic (/dʒʊˈræsɪk/ juurr-ASS-ik) is a geologic period and stratigraphic system. It lasted from the end of the Triassic Period 201.4 Ma (million years ago) to the start of the Cretaceous Period, 143.1 Ma. It was the middle period of the Mesozoic Era. It is named after the Jura Mountains, where scientists found rocks from this time.

During the Jurassic, the big land called Pangaea began to split into two parts: Laurasia to the north and Gondwana to the south. The climate was warmer than today, with no ice caps. Forests grew even near the poles.

This time was famous for its amazing dinosaurs. The first stem-group birds appeared, coming from a group of theropod dinosaurs. The oceans had interesting marine reptiles such as ichthyosaurs and plesiosaurs. Pterosaurs ruled the skies. Many modern plants, like conifers, also began to appear during the Jurassic.

Etymology and history

The word "Jurassic" comes from the Jura Mountains, a mountain range between France and Switzerland. In 1795, a scientist named Alexander von Humboldt noticed special rocks there and called them Jura-Kalkstein, meaning "Jura limestone".

Later, in 1829, another scientist, Alexandre Brongniart, used the term terrains jurassiques to describe similar rocks in Britain, which means "Jurassic terrains". Other scientists helped name different parts of the Jurassic period using fossils they found.

Geology

The Jurassic Period is divided into three epochs: Early, Middle, and Late. It is also split into the Lower Jurassic, Middle Jurassic, and Upper Jurassic series. Geologists study the rocks from this time and call them stages. These stages match up with time periods.

Scientists use fossils called ammonites to help date the rock layers. The first appearance of certain ammonite types marks the start of each stage. These zones help experts compare rock layers from different places.

The Jurassic had important resources like oil and coal. Large oil fields, such as the Ghawar Field, formed during this time. Coal was found in places like north-west China, especially in the Turpan-Hami Basin and the Ordos Basin.

Some big impacts from space happened during the Jurassic. One was the Morokweng impact structure in South Africa, and another was the Puchezh-Katunki crater in Russia.

Paleogeography and tectonics

At the start of the Jurassic, all the big lands of the world were joined together in a huge supercontinent called Pangaea. During this time, Pangaea started to split into two smaller landmasses: Laurasia in the north and Gondwana in the south. The first split happened between North America and Africa, making the early Atlantic Ocean.

The Jurassic had many changes in how the Earth’s lands and oceans looked. The Atlantic Ocean was still very narrow, and the Tethys Ocean was between Gondwana and Asia. Europe was a chain of islands surrounded by shallow seas. Both the North and South Poles were covered by oceans. By the end of the Jurassic, Madagascar and Antarctica began to move away from Africa, and North America and South America had separated to make a seaway linking the Atlantic to the big ocean, Panthalassa.

Climate

The climate during the Jurassic period was warmer than today, about 5–10 °C warmer. There was more carbon dioxide in the air. Even places near the poles had forests. They had warm summers and cold winters, but there were no big ice sheets. The oceans were warmer, and coral reefs grew farther from the equator.

There were times when the climate got cooler for a short time. One big event was the Toarcian Oceanic Anoxic Event. During this time, a lot of carbon dioxide made the temperatures very warm and changed the oceans. This affected many sea creatures. By the end of the Jurassic, the climate began to cool and led into the Early Cretaceous period.

Flora

At the start of the Jurassic period, there was no big die-out of plants. Some plant groups, like the Peltaspermaceae, went extinct, while others, like Dicroidium, declined but survived in some places.

Conifers were very important plants during the Jurassic. Many modern conifer groups, like Araucaria and Cupressaceae, first appeared during this time. Other conifer families, such as Cheirolepidiaceae and Pinaceae, were also common. Ginkgoales, which today include only the Ginkgo tree, were more diverse back then. Bennettitales, plants that looked like cycads but were different, were also common and had flower-like structures. Cycads were around, but not as dominant as once thought.

Ferns and their relatives, such as the families Dipteridaceae and Osmundaceae, were widespread. The first modern horsetails of the genus Equisetum appeared in the Early Jurassic. Simple plants like mosses, liverworts, and Quillworts that are similar to modern species were also present during this time.

Fauna

Dinosaurs continued to thrive during the Jurassic period, becoming the main land animals. After the end of the Triassic, many new kinds of dinosaurs appeared. Theropods, such as coelophysoids and dilophosaurs, showed up early. Later, groups like ceratosaurs and tetanurans developed. Sauropods grew very big, some becoming the largest land animals ever.

Other reptiles also changed in many ways. Crocodylomorphs, the ancestors of today's crocodiles, lived in different places, both on land and in water. Pterosaurs, with their wing skins, flew in the sky. Marine reptiles like plesiosaurs and ichthyosaurs swam in the oceans. These changes made the Jurassic a busy and full time for Earth's plant and animal life.