The uppermost layer over the Earth's surface is called the Crust.

The Earth is composed of several layers, each with its own unique characteristics. The crust is the outermost layer and is the thinnest layer of the Earth, making up less than 1% of its total volume. It is also the layer that we interact with directly, as it is where the continents, oceans, and landforms are located.

The crust can be further divided into two types: the continental crust and the oceanic crust.

1. Continental Crust:
- The continental crust is primarily composed of granitic rocks, which are less dense than the rocks found in the oceanic crust.
- It is thicker than the oceanic crust, ranging from 25 to 70 kilometers in thickness.
- The continental crust is less dense and more buoyant than the underlying mantle, which allows it to "float" on top.

2. Oceanic Crust:
- The oceanic crust is primarily composed of basaltic rocks, which are denser than the rocks found in the continental crust.
- It is thinner than the continental crust, ranging from 5 to 10 kilometers in thickness.
- The oceanic crust forms the floors of the ocean basins and is constantly being created and destroyed through the process of seafloor spreading and subduction.

The crust is also characterized by its tectonic activity, which is responsible for the formation of mountains, earthquakes, and volcanic activity. The movement and interaction of the crustal plates, known as plate tectonics, is driven by the underlying convective currents in the mantle.

In conclusion, the uppermost layer over the Earth's surface is called the crust. It is divided into the continental crust and the oceanic crust, both of which have distinct compositions and characteristics. The crust is the layer we interact with directly and is responsible for the formation of landforms and tectonic activity.