World's first massacre in recorded history?

Which of these events occurred earliest in the history of earth?

(a) Evolution  of animals

(b) Oxygen formation

(c) Colonization of land 

(d) First human

3. Based photographic evidence. Human Rights Watch estimates that 6,786 individuals died in Syrian detention centers or hospitals run by the government between 2011 and 2013. What happened to Mohammed at the first of five detention centers where he was imprisoned?