Mass Effect 2 & Mass Effect 3
The sister tragedy to the extinction event on Aphras, Tosal Nym was the rarest of jewels; a second garden planet within the same life zone as Aphras. Not as old as it's sister planet, its fossil evidence indicates it was home to abundant invertebrate sea life.
However, similar craters to those on Aphras created a dust shroud that killed 99% of biota on the planet. The even spacing of the craters indicates a coordinated, simultaneous attack from points around the globe, rather than an asteroid collision or supervolcanic scenario.