When Charles Darwin wrote The Origin of Species, the oldest known fossils were trilobites preserved in rocks deposited during the Cambrian Period. Many decades and countless discoveries later, fossils from six continents now extend the animal record backward into the Ediacaran Period, some 50 million years before the first trilobites. Andrew H. Knoll of Harvard University traces the fossil record of Earth’s earliest known animals, asking how these remains illuminate the early evolution of our own kingdom.