Which major extinction event do some researchers think might have occurred due to a GRB? How would the GRB have affected the Earth to produce that mass extinction?

Paragraph 2: (Use Sources 3, 4, 5 and Wikipedia.)
• Define the term “GRB” and what astronomers think happens in order to produce one.
• Did the Earth experience one in the Eighth Century? Describe what some researchers suggest is evidence that one did strike the Earth at that century.
• Which major extinction event do some researchers think might have occurred due to a GRB? How would the GRB have affected the Earth to produce that mass extinction?