Overview of our models for gas disk and particle evolution in different disk regions. The blue and yellow particles represent silicates with and without refractory carbon. The light blue particles represent icy pebbles. The pink particles show the oxygen atoms that are formed by the destruction of oxygen molecules because of the FUV radiation which is described as red arrows. The light blue dashed line is the snow line. Icy pebbles enclosing many small silicates drift to the snow line (blue dashed line) from the outer region. Orange upper and lower layers are FUV-exposed regions, where oxygen atoms exist.