Tracing the physical and chemical evolution during low-mass star formation

The expected evolution during the early stages of star formation will be reviewed and compared to observations. During the infall phase, a given parcel of gas will encounter regions of enhanced density, temperature, and velocity gradient.  The changes cause evolution in the chemical state, as gas freezes onto dust grains, reacts to form more complex species, which may be released back into the gas phase. When the material reaches the disk, further evolution occurs. These expectations will be compared to observations. The data suggest repeated cycles of heating and cooling, which can drive further complexity in both the ice and gas phase. The cycling into complex organics in the disk, along with rapid dust grain growth can cause serious underestimations of disk masses.