Part 1 Printing the Circuit Board. 1. Choose a method to use for creating the PCB. Your choice will usually be based on the availability of materials needed by the method, the technical difficulty level of the method or the quality of PCB you desire to obtain.
Permian-Triassic Extinction. In this video segment from Evolution: Extinction!, geologist Peter Ward shows rock layers laid down during the Permian and Triassic periods. The Permian layers contain abundant animal fossils and fossilized traces of animals, while the Triassic layers are almost devoid of fossils, suggesting a mass extinction event occurred 250 million years ago, at the end of the Permian.
It is believed that Dinosaurs mass extinction happened 65 million years ago which ended the Mesozoic era. Only at the end of the nineteenth century did paleontologists realize that nearly all dinosaurs had gone extinct within a brief period of tim... This page may be out of date. Save your draft before refreshing this page.