Blog5 geologic periods

Describe on of the geologic periods what organisms dominated, what was introduced, what died out? Be sure to include pictures.

The Mesozoic Era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is one of three geologic eras of the Phanerozoic Eon. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time.   There were three geologic periods in the Mesozoic Era -Triassic,Jurassic, and Cretaceous.


Triassic: The Triassic is a geologic period and system that extends from about 250 to 200 Mya(million years ago).   It is the first geologic period of the Mesozoic era.The first true mammals also evolved during the Triassic, as well as the first flying vertebrates, the pterosaurs. The vast supercontinentof Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south.The Triassic period ended with a mass extinction, which was particularly severe in the oceans; the conodonts disappeared, and all the marine reptiles except ichthyosaurs and plesiosaurs. Invertebrates like brachiopods, gastropods, andmolluscs were severely affected. In the oceans, 22% of marine families and possibly about half of marine genera went missing according to University of Chicago paleontologist Jack Sepkoski.

Jurassic: The Jurassic is a geologic period and system that extends from about 199.6± 0.6 Mya(million years ago) to 145.5± 4 Mya. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The dinosaurs continued to dominate the land, and reached their peak in this period as they diversified into a wide variety of groups, ranging from the carnivorous theropods to the massive, herbivorous sauropods. The first birds appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Marine reptiles such as ichthyosaurs and plesiosaurs ruled the oceans, while the flying reptiles called pterosaurs continued to dominate the skies.  There was a minor mass extinction toward the end of the early Jurassic period (roughly 190-183 million years ago) in which more than 80% of marine bivalve species (like many clams) and many other shallow-water species died out. The cause of this extinction is unknown, but there is some speculation (by sedimentologist Stephen P. Hesselbo et al.) that it was triggered by the release of huge methane deposits from within the Earth (these deposits formed beneath the seabed as surface algae dies and sinks to the sea floor).


Cretaceous :The Cretaceous was a period with a relatively warm climate and high eustatic sea level. The oceans and seas were populated with now extinct marine reptiles, ammonites and rudists; and the land by dinosaurs. At the same time, new groups of mammals and birds as well asflowering plants appeared. The Cretaceous ended with one of the largest mass extinctions inEarth history, the K–T extinction, when many species, including non-avian dinosaurs,pterosaurs, and large marine reptiles, disappeared.