You're likely thinking of the Earth's mantle, which is a solid, rocky layer that makes up the majority of Earth's volume. While it's solid, it's not like a rock you can pick up. It's more like a very thick, viscous fluid that can flow over extremely long periods.

Here's why the mantle isn't considered plastic:

* It's not actually plastic. Plastic is a synthetic material. The mantle is composed of minerals like silicate rocks.

* It doesn't have the same properties as plastic. Plastic is flexible and can be molded. The mantle is solid but can flow very slowly due to extreme heat and pressure.

Let me know if you have any other questions!