Here's why:
* Earth's Formation: Earth formed from a swirling cloud of dust and gas about 4.5 billion years ago. The heavier elements like iron and nickel sank to the center, forming the core. Lighter elements rose to the surface, creating the crust.
* Geological Time: The process of the Earth forming and evolving is a slow one, measured in billions of years.
* Layers of the Earth: The layers of Earth are arranged by density, with the densest materials at the core and the least dense materials at the crust. This means the Earth's core (the innermost layer) formed first and is the oldest, while the crust is the youngest layer.
So, the layers furthest from the crust are the core and mantle, which are significantly older than the crust.