Jurassic
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The Jurassic is one of the major geological periods in Earth's history. It is the second of three periods comprising the Mesozoic Era, situated between the earlier Triassic and the later Cretaceous. The name derives from the Jura Mountains, located between France and Switzerland, where rocks of this period were first clearly studied.
The period began approximately 201 million years ago and ended approximately 145 million years ago. Its beginning is marked by the mass extinction at the end of the Triassic, which opened new spaces for life to spread. The Jurassic is divided into three subdivisions: Early, Middle, and Late.
Continental configuration and climate
In the early Jurassic, the large supercontinent Pangaea began to break apart. It separated into Laurasia in the north and Gondwana in the south, while the Atlantic Ocean began its early opening. This fragmentation caused seas to inundate continents and the climate to become warmer and more humid compared to the arid Triassic. Many areas of land had shallow seas, with little to no polar ice.
Life on land
The Jurassic is known for the flourishing of dinosaurs. These included large sauropods with long necks such as Diplodocus and Brachiosaurus, herbivores such as Stegosaurus, and carnivores such as Allosaurus. The period also saw the emergence of the first birds; Archaeopteryx, found in Germany, is one of the celebrated examples of the transition between dinosaurs and birds. Mammals existed but were generally small.
Marine life
The Jurassic seas contained large reptiles living in the water, such as ichthyosaurs and plesiosaurs, and diverse fish. Ammonites—coiled-shelled organisms—were abundant and aid scientists in determining the age of rock layers through biostratigraphy. Reefs and microscopic marine life produced limestone deposits now found as fossils.
Rocks and resources
Jurassic rocks are found in Europe, North America, China, and Africa. Much of the oil and natural gas extracted from the North Sea and Persian Gulf comes from Jurassic rock layers. These rocks are also important sources for paleontological research.