Gaia is being sold and licensed to the end user under the Unity asset store license: https://unity3d.com/legal/as_terms.

Portions of this asset were created under usage of additional resources provided by Unity. The files found in the following folders are governed by additional licenses:

Folder:
Procedural Worlds\Gaia\Scripts\Mesh Simplifier
Derived from the project "Unity Mesh Simplifier", obtainable from: https://github.com/Whinarn/UnityMeshSimplifier
License: MIT License, see Procedural Worlds\Gaia\Scripts\Mesh Simplifier\license.txt
Please see also: Procedural Worlds\Gaia\Scripts\Mesh Simplifier\Third Party Notices.txt

Folder: 
Procedural Worlds\Gaia\Shaders\Unity\Standard Shaders
Derived from the Unity Standard Shaders package obtainable from: https://unity3d.com/get-unity/download/archive
License: see Procedural Worlds\Gaia\Shaders\Unity\Standard Shaders\license.txt

Folders: 
Procedural Worlds\Gaia\Shaders\Unity\Terrain Tools
Procedural Worlds\Gaia\Scripts\Unity\Terrain Tools
Procedural Worlds\Gaia\Gaia Pro\Scripts\Unity\Terrain Tools
Procedural Worlds\Gaia\Gaia Pro\Shaders\Unity\Terrain Tools
Derived from the Unity Terrain Tools Package
License: Unity Companion License - https://unity3d.com/legal/licenses/Unity_Companion_License
A full "offline" copy of this license can be found in each of these folders as well.