The beginning and end of each chunk of time in the geologic time scale is determined by when some species appeared or disappeared from the fossil record. When many species went extinct around the same ...

As a period of geologic time, the boundaries of the Triassic are defined on the basis of rocks and the fossil record. It was the German geologist Friedrich August von Alberti who first marked the ...

Late Ordovician Period - The Ordovician Period refers to the interval of geologic time from approximately 505 to 438 million years ago and is sometimes called the "age of marine invertebrates". Late ...

The Cretaceous is a geological period that began 145 million years ago and ended 66 million years ago. It is the last period in the Mesozoic Era. It comes after the Jurassic Period and before the ...

According to this view, a once-tumultuous period of change had slowed to ... aspects of the forces Lyell believed had operated over geological time to produce the world we see now.

John Wesley Powell A professor of geology at Illinois Wesleyan ... A shallow sea advances and retreats several times during this period, leaving behind the layers named Kaibab Limestone, Toroweap ...

Research suggests that tropical riparian ecosystems – those found along rivers and wetlands – recovered much faster than expected following the end-Permian mass extinction around 252 million years ago ...