The question of when animals first evolved is one that has confounded scientists since the time of Charles Darwin. Studying rocks in north Wales in the mid-18th century, Darwin found the sudden first appearance of animal shells and skeletons in layers dating back over 500 million years perplexing. He had predicted a long history of evolution, with animals slowly gaining complexity through time, rather than this apparent instantaneous appearance of complex animals.
The sudden appearance of complex animals has led scientists to argue that animals must have a “hidden history”, a period in Earth’s past prior to their fossil record where they existed but have left no trace of their presence in the rocks. Our new study may help scientists understand how long this hidden history may have lasted.
