This question can be interpreted in a few ways! Here's a breakdown:

1. If we're talking about layers from the surface inwards:

* The crust is the outermost layer of the Earth, what we walk on.

2. If we're talking about the order of formation:

* The core formed first during the Earth's formation. The heavy elements sank to the center, while lighter elements formed the mantle and crust later.

3. If we're talking about a specific layer within a broader context:

* For example, if we're talking about the layers of the atmosphere, the troposphere is the lowest layer.

Let me know if you had a specific layer in mind, and I can give you a more precise answer!