 While some geological evidence was presented to suggest that earlier fossils did exist , for a long time this evidence was widely rejected . Fossils from the Ediacaran period , immediately preceding the Cambrian , were first found in 1868 , but scientists at that time assumed there was no Precambrian life and therefore dismissed them as products of physical processes . Between 1883 and 1909 Walcott discovered other Precambrian fossils , which were accepted at the time . However , in 1931 Albert Charles Seward dismissed all claims to have found Precambrian fossils . In 1946 , Reg Sprigg noticed " <unk> " in rocks from Australia 's Ediacara Hills . However , while these are now recognized as coming from the Ediacaran period , they were thought at the time to have been formed in the Cambrian . From 1872 onwards small shelly fossils , none more than a few millimeters in size , were found in very Early Cambrian rocks , and later also found in rocks dating to the end of the preceding Ediacaran period , but scientists only started in the 1960s to recognize that these were left by a wide range of animals , some of which are now recognized as molluscs . 
