Image: “Trilobite,” by Heinrich Harder, 1916 (probably), from “The Wonderful Paleo Art of Heinrich Harder,” in Wikimedia Commons … https://commons.wikimedia.org/wiki/File:Trilobite_Heinrich_Harder.jpg … public domain … DESCRIPTION: The Trilobite was an ancient arthropod. The earliest sign of trilobites on Earth was about 521 million years ago, during the Early Cambrian period. There were very many different types of trilobites in the seas of Earth during the lower Paleozoic age. About 250 million years ago, during the Permian age, they are thought to have become extinct. We know for sure, then, that there were trilobites on earth for about 271 million years. –from “Trilobite” in English Wikipedia … https://en.wikipedia.org/wiki/Trilobite ..

Image: Level 3 icon [adapted], by Us