The Snowball Earth hypothesis proposes that, during one or more of Earth's icehouse climates, the planet's surface became entirely or nearly entirely frozen.It is believed that this occurred sometime before 650 M.Y.A. (million years ago) during the Cryogenian period. Proponents of the hypothesis argue that it best explains sedimentary deposits that are generally believed to be of …

The Ordovician is the second period of the Paleozoic era and the Phanerozoic eon.It lasted from about 485.4 million years ago (mya) to 443.4 mya. It follows the Cambrian period and is followed by the Silurian period.. The Ordovician was named after the Welsh tribe of the Ordovices.It was defined by Charles Lapworth in 1879.

The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Paraves. Birds are categorized as a biological class, Aves.For more than a century, the small theropod dinosaur Archaeopteryx lithographica from the Late Jurassic period was considered to have been the earliest bird. Modern phylogenies place birds in the …

Classification and systematics. The Demospongiae have an ancient history. The first demosponges may have appeared during the Precambrian deposits at the end of the Cryogenian "Snowball Earth" period. Their presence has been indirectly detected by fossilized steroids, called steranes, hydrocarbon markers characteristic of the cell membranes of the sponges, rather …

The Sturtian glaciation was a glaciation, or perhaps multiple glaciations, during the Cryogenian Period when the Earth experienced repeated large-scale glaciations. The duration of the Sturtian glaciation has been variously defined, with dates ranging from 717 to 643 Ma. Stern et al. place the period at 715 to 680 Ma.. According to Eyles and Young, "Glaciogenic rocks figure …

The Coniacian is an age or stage in the geologic timescale.It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded …

East Greenland Orogen – From Cryogenian to Devonian Periods; Taconic phase – Mountain-building period that affected most of New England – In the northeastern U.S. and Canada, during the Ordovician Period; Acadian phase – North American orogeny – In the eastern U.S., during the Silurian and Devonian Periods

The Andean-Saharan glaciation occurred during the Paleozoic from 450 Ma to 420 Ma, during the Late Ordovician and the Silurian period. For the Ordovician/Saharan part, see the more extensive article on the Late Ordovician glaciation.. Description. According to Eyles and Young, "A major glacial episode at c. 440 Ma, is recorded in Late Ordovician strata (predominantly Ashgillian) in …