Historical clue formulations

• What sets things in motion — 2016-02-08
• Spark — 2014-11-21
• It makes things happen — 2014-10-28
• Prompter — 2012-01-20
• Spark — 1997-10-18
• Instigator — 1995-01-04
• Part of a chemical reaction — 1994-04-17