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.
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the amount of life on Earth.Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. This extinction event lasted perhaps as long as 20 million years, and there is evidence for a series of extinction pulses within this period. 2  OrdovicianâSilurian extinction events (End Ordovician or O-S): 450â440 Ma at the Ordovician-Silurian transition.