The impacts are very specific meteorological collisions which have had a significant effect on human life on the planet, in both its lifetime and creating the conditions for it to have come about.
The First Impact
About four billion years ago, a large object collided with Earth and devastated the surface, sending debris into the orbit around the planet. This debris would later condense to form the moon.
The Second Impact
2001, a micrometeor too small to be picked up by detection equipment slipped by Earth’s defenses and collided with the south pole at near the speed of light. The entirety of the continent was devastated, the initial hear melting much of it and causing worldwide devastation as the sea levels rose.
The debris thrust into the atmosphere from this would later form the barrier in the sky which would block the sun and create the Fimbulvetr.