A glacial period.

The geological period from 500 to 435 million years ago.

It is a period of geological time which extends from 495 to 440 million years ago.

The second earliest period of the Paleozoic era (after the Cambrian and before the Silurian) 458-438 million years ago.

n. The second (510 to 439 millions years ago) of six periods that constitute the Palaeozoic Era, named after an ancient Celtic tribe, the Ordovices. The Ordovician follows the Cambrian and precedes the Silurian. It is noted for the presence of various rapidly evolving graptolite genera and of th e earliest jawless fish.

A period of geological time, dating from about 490 to 440 million years ago.

The second earliest period of the Paleozoic era (after the Cambrian and before the Silurian), thought to have covered the span of time between 490 and 443 million years ago; also, the corresponding system of rocks. It is named after a Celtic tribe called the Ordovices. In the older literature the Ordovician is sometimes know as the Lower Silurian .

Period of geologic time 430-500 million years ago.

The second of the six Geologic Periods of the Paleozoic Era. It extends from the end of the Cambrian Period (about 500 million years ago) to the beginning of the Silurian Period (about 435 million years ago).

from 500 million to 425 million years ago; conodonts and ostracods and algae and seaweeds

Unit of rocks identified by Charles Lapworth and named for a tribe of people that lived in Wales and were called the Ordovices. Overlies the Cambrian in the Paleozoic.

The geological time period dating from 439-510 million years ago.

the second epoch of the Palaeozioc era lasting 60 million years during which marine invertebrates flourished; named after the native British Ordovices tribe which inhabited the area in North wales where outcrops of these rocks occur.

The geological period between about 510 million years to 439 million years ago.

The second earliest period of the Paleozoic era, spanning the time between 505 and 440 million years ago. It is named after a Celtic tribe called the Ordovices.

A Period in the Paleozoic Era that includes the time interval from about 505 to 438 million years ago. more details...

(see Geological Timescale)

the second-oldest time period of the Paleozoic Era. It covers the span of time from about 500 Ma to about 440 Ma.

Rocks pertaining to the Ordovician Period, which dates from 510 million to 439 million years ago. The oldest rocks that crop out in Indiana are Ordovician in age.

Geological period 525 – 440 million years ago.

the period of geological time between 505 and 440 million years ago. The name comes from the Ordovices, a Celtic tribe which lived in Wales in the region where these rock units were first defined. See Geological Timescale. Page up

Early Paleozoic age ranging from 500 Ma to 435 Ma.

The second period of the Paleozoic, c. 490-442 Mya.

A early period of time stretching from 495 - 443 million years ago.

a geological period, the second in the Paleozoic era, after the Cambrian and before the Silurian. The Ordovician is characterized by the appearance of jawless fishes and the development of many trilobites, brachiopods and other invertibrates; the rocks formed in this period. [AHDOS

The Ordovician period is the second of the six (seven in North America) periodsThe Carboniferous in North America is divided in two, the Mississippian and the Pennsylvanian. of the Paleozoic era. It follows the Cambrian period and is followed by the Silurian period. The Ordovician, named after the Welsh tribe of the Ordovices, was defined by Charles Lapworth in 1879, to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian periods respectively.