Solar flares destroying power grids and pelting the Earth with city-sized fireballs? Massive meteor showers? One huge meteor as big as Texas? Could there be a change in the composition of the sun resulting in massive overheating / supernovae or cooling off to a dim red? Rogue planet entering our solar system in near collision with the Earth?

What if the Earth’s core stops spinning and the Earth’s magnetic field disappears. When that happens, compasses will stop pointing north, birds will not know where to fly when they migrate, and the Earth’s atmosphere will disappear.

Or, maybe humans lose the ability to reproduce—or some other animal or insect becomes the dominate species. Or some horrific pandemic kills large amounts of life.

What things are possible but unlikely, and what would the result be on any of these or other possibilities?