cause of depression
if one person has mix emotion, and feels like it ends of the world they commit if this is the case you have to keep your eye on him or her..and start talking and convince this person to clarify that he or she can make it through gods help and their family, frends and every person that love them realize how precious our life
the other one is the protoplanet hypothesis, it is similar with the nebular theory but its more elaborated.
planetisimal and tidal theories
not sure with the info for the third one.