Thermal processing of icy grains. Panel a shows the state of the disk before a stellar outburst. The blue dash line represents the water ice line, the gray dashed line the radial location (r_υ=0) that separates the inward- and outward-drifting pebbles, and the black-outlined region the terrestrial-planet-forming region. During an outburst (panel b) the ice line moves outward and particles in the inner disk lose their icy mantles containing isotopically anomalous grains. Afterward, the disk cools down and the iceline retreats (panel c) resulting in the inner disk with a mixture of processed and unprocessed grains, altering the solid composition from NC- to OC-like. However, on longer timescales evermore unprocessed pebbles drift inward resulting in a pebble composition that is close to CI outside the water ice line (panel d).