The Jurassic Period is a major unit of the geologic
time scale that extends from about 200 to 145 Ma, the
end of the Triassic to the beginning of the
Cretaceous. As with other geologic periods, the rock
beds that define the start and end of the period are
well identified but the exact dates are uncertain by 5 -
10 million years. The Jurassic constitutes the middle
period of the Mesozoic era, also known as the "Age
of Dinosaurs". The start of the period is marked by
the major Triassic-Jurassic extinction event.
The Jurassic was named for the extensive marine
limestone exposures of the Jura Mountains, in the
region where Germany, France and Switzerland
meet. Very limited outcrops of Jurassic age rocks
occur in Hell’s canyon, south of Moscow.
This period extends roughly from 150 to 200
million years ago.
A range composed of Jurassic rocks in the Alps.
Location of an outcrop of Jurassic rock in Idaho.
During the early Jurassic, the supercontinent Pangaea
broke up into the northern supercontinent Laurasia
and the southern supercontinent Gondwana; the Gulf
of Mexico opened in the new rift between North
America and what is now Mexico's Yucatan
Peninsula. The Jurassic North Atlantic Ocean was
relatively narrow, while the South Atlantic did not
open until the following Cretaceous Period, when
Gondwana itself rifted apart. The Tethys Sea closed,
and the Neotethys basin appeared. Climates were
warm, with no evidence of glaciation. As in the
Triassic, there was apparently no land near either
pole, and no extensive ice caps existed.
The Jurassic geological record is good in western
Europe, where extensive marine sequences indicate a
time when much of the continent was submerged
under shallow tropical seas; famous locales include
the Jurassic Coast World Heritage Site and the
renowned late Jurassic Solnhofen fossils.
In contrast, the North American Jurassic record is
the poorest of the Mesozoic, with few outcrops at the
surface. Though the epicontinental Sundance Sea left
marine deposits in parts of the northern plains of the
United States and Canada during the late Jurassic,
most exposed sediments from this period are
continental, such as the alluvial deposits of the
The first of several massive batholiths were emplaced
in the northern Cordillera beginning in the mid-
Jurassic, marking the Nevadan orogeny.
During this period, Pangea broke up into
Gondwana and Laurasia, forming the Gulf of
A world famous Jurassic limestone for fossil
vertebrates in Europe.
A Jurassic marine deposit in the northern plains.
A famous Jurassic alluvial formation for dinosaur
bones in the western States.
During the Jurassic, the primary vertebrates living in
the seas were fish and marine reptiles. The latter
include ichthyosaurs, plesiosaurs and marine