It seems like you're asking about why scientists believe that rocks and the Earth are similar. It's important to clarify this point, as the question as it stands is a bit confusing.

Here's a breakdown of what you might be asking, and the answers:

1. Rocks as building blocks of the Earth:

* The Earth is composed of rocks: It's true! The Earth's crust, mantle, and even parts of the core are made up of various types of rocks. So, in this sense, rocks are fundamental to the Earth's composition.

2. Rocks as a window into the Earth's history:

* Rocks tell us about the Earth's past: Scientists study rocks to understand how the Earth formed, how continents moved, and how life evolved. Rocks contain clues about past environments, climates, and geological events.

3. Rocks and their composition:

* Rocks and the Earth share similar elements: The Earth and the rocks that make it up are composed of the same fundamental elements. While the ratios of these elements can vary, the overall composition is quite similar.

4. The Earth's interior and rocks:

* We learn about the Earth's interior through rocks: We can't directly observe the Earth's core and mantle, but we can analyze rocks that come from deep within the Earth (like volcanic rocks) to gain insight into their composition and processes.

It's important to remember that the Earth is a complex system, and rocks are just one component. While they offer crucial clues about the Earth's formation and history, it's not simply a matter of rocks being "similar" to the Earth.

If you'd like to discuss any of these points further, or if you had something else in mind, please let me know!