1. Layer 1 (Uppermost Layer): This is the sediment layer, consisting of unconsolidated sediments like clay, sand, and shells. It's generally thinner than the other layers, but its thickness varies depending on the age of the oceanic crust.

2. Layer 2 (Intermediate Layer): This is the pillow basalt layer, composed of solidified lava flows that erupted onto the ocean floor. It's characterized by its pillow-like structures formed during underwater volcanic eruptions.

3. Layer 3 (Lowermost Layer): This is the gabbro layer, consisting of a denser, crystalline rock that forms from the slow cooling of magma beneath the ocean floor. It's the thickest and most extensive layer of the oceanic crust.

It's important to note that these layers are not always clearly defined, and their thickness can vary significantly across different regions of the ocean.