In my universe a race of humanoid beings caused 3 planets:
- a larger rocky planet
- and another earth sized rocky planet
to crash and collide into each other, but still allowed the humanoid beings, humans, and some microscopic plants and animals to survive.
The larger rocky planet is a red, dusty, hot, volcanic planet with little oxygen but has microscopic life inhabiting it, while the other earth sized planet is a blue, cold, oxygen rich planet that has a moderate amount of water and has larger life forms.
Also the two planets that aren't Earth come from a different solar system from earth, but these two planets come from the same solar system as each other (or possibly not if it causes the whole collided combined planets thing to become impossible), but they're all in the same galaxy.
After the three planets collide and merge, they become a large rocky planet with the highest part atmosphere having the qualities of the blue planet, the point closest to the planet's core having the qualites of the red planet, the surface of the planet to have the qualites of earth, and a point between the surface and the core to have a dramatic mixture of the three.
Soon after the collision, almost all of the planet's surface is water, but after a very long time, moss-like plants start to grow over it, and help shelter microscopic life from the harsh environments of the collision's aftermath, and soon the microscopic life would start to evolve into visible plants, animals, and eventually humanoids.
Also at some point after this point, humans from advanced technology underground bunkers are able to head back to the surface without all of them all dying instantly.
Is there a possibile scientific way for all of this to happen?