The area had repeatedly been smothered in volcanic ash by eruptions in Inner Mongolia 124 million years ago, during the Lower Cretaceous. The fine-grained ash preserved the living organisms that it buried in fine detail. The area was teeming with life, with millions of leaves, angiosperms (the oldest known), insects, fish, frogs, salamanders, mammals, turtles, lizards and crocodilians discovered to date.