The Lower Jurassic is the first geological epoch in the Jurassic that began 201.3 million years ago, and ended at 174.1 million years ago.
The Jurassic period is divided into Lower, Middle and Upper. The Lower Jurassic started after the end-Triassic extinction event at 201.3 million years ago (mya). Its rocks form in Europe the Lias group of marine strata consisting mostly of limestone, with some clays and siltstone. It was in this formation on the Dorset Jurassic Coast that Mary Anning did much of her work. The mudstones of the earliest Jurassic (Blue Lias) give way to carbonate rocks as the water deepens in the Middle Jurassic.
The Jurassic period was one of the time periods when dinosaurs were on the Earth. By this time, many groups of the Triassic period had become extinct.
At the start of the Jurassic, Britain was warm temperate to subtropical, between 30° and 40° north of the equator. Temperature would have been in the range of 12–29°C.
Shallow seas were over southern England; higher ground like the Mendip Hills were a string of islands stretching westwards South Wales.
The Lower Jurassic in western North America is quite different. It is continental in origin, sandstones laid down in shifting streams and rivers. These sandstones were laid down over a long period from the later Permian to the Lower Jurassic.