What action must you take to give your text depth once it is converted to a 3D layer?

To give your text depth after converting it to a 3D layer in Adobe After Effects, the action that needs to be taken is to extrude the layer. Extrusion is the process of adding depth to a 2D layer, transforming it into a 3D object that can be viewed from different angles. This allows for more dynamic visual effects, as you can manipulate the text in 3D space, adding realism and importance to the design.

When you extrude text, you essentially create a 3D shape based on the original 2D text. This capability opens up a variety of possibilities for animation, lighting effects, and interactions with other 3D layers in your composition. By extruding, you can also add bevels and modify the geometry of the text for a more polished and stylized look.

Other actions like adjusting opacity or applying a gradient primarily affect the appearance and opacity of the layer's surface but do not inherently add depth. Animating the layer can create movement but does not contribute to an increase in the layer's dimensionality. Consequently, while those actions can enhance your design, they do not fulfill the requirement of adding depth to the text as effectively as extruding does.