The Cretaceous - Tertiary boundary can be easily observed in the rock layers. The geological signature is a thin band of rock. The thin band of rock is easily distinguishable from the other layers as it also has much darker color. The amount of carbon in this layer is much higher, and there is also zirconium, which usually is not found on Earth as it is extremely rare. The reasons to why this boundary has formed are the asteroid impact and the immense volcanic activity that it triggered.