The oldest crinoid fossil, Guensberg said, is from the Cambrian period about 530 million years ago. But as a class Crinoidea flourished in the Ordovician period, 450 to 380 million years ago.

It came during the Ordovician period, right after the Cambrian came to a close 485 million years ago. The Ordovician Radiation, also called the Great Ordovician Biodiversification Event ...

After the Ordovician Period came the Silurian Period (443.8 million to 419.2 million years ago), which saw the spread of jawless fish throughout the seas.

The researchers' idea that Earth once had rings comes from reconstructions of Earth's plate tectonics from the Ordovician period—which ran between 485.4 million years and 443.8 million years ago ...

During the Ordovician period, the concentration of CO2 in the earth's atmosphere was about eight times higher than today. It has been hard to explain why the climate cooled and why the Ordovician ...

Two intense spells of volcanic activity 450 million years ago triggered a period of global cooling and falling oxygen levels in the oceans, leading to the extinction of 86 percent of all marine life.

During the Ordovician period, the concentration of carbon dioxide in Earth's atmosphere was about eight times higher than today. It has been hard to explain why the climate cooled and why the ...

The Silurian Period occurred from 443.8 million to 419.2 million years ago. It was the third period in the Paleozoic Era. It followed the Ordovician Period and preceded the Devonian Period. During ...

Scientists studying the geology of the Ordovician Period about 466 million years ago report evidence that Earth's ring system created a telltale pattern of impact craters, and it may also explain ...

The Paleozoic era's Silurian period saw animals and plants finally emerge on land. But first there was a period of biological regrouping following the disastrous climax to the Ordovician. The ...