The animal kingdom experienced a massive diversification in the early Cambrian Period, between approximately 541 and 520 million years ago (Ma). During this 21-million-year interval, many animal phyla—each characterized by a unique body plan—diverged. This diversification event, dubbed the Cambrian explosion, has been a subject of intensive debate among bioscientists and geoscientists. In 1859, Charles Darwin speculated that the Cambrian explosion was an artifact due to the preservational failure of early animals that lacked hard skeletons. According to Darwin, animals evolved long before the Cambrian explosion, but they left no fossil record. In the past 150 years, paleontologists have thoroughly investigated many Precambrian successions in search of early animals. Among the many findings, the discovery of soft-bodied Ediacara fossils is arguably the most significant.