Earth is about 4.5 billion years old, and as the eons passed, the crust of the young planet experienced turbulence. The oldest crust on our planet formed during what is known as the Hadean epoch. Anything found to have been part of our planet’s crust in the distant past was 3.8 billion years old or younger. However, samarium isotopes had left behind chemical signatures of their decay into isotopes of neodymium. Two different isotopes of neodymium which had come from two samarium isotopes were both dated to 4.16 billion years.