The film ends with the total annihilation of Earth and, for the saved ones, the vision of a new, unspoilt world. The film's title screen/logo contains the ending/twist (a planet eclipsed by a sun).

What happened at the end of the knowing?

They save Caleb and Abby, leaving John to die along with most of mankind in the solar flare event, and the children are taken to safety on a heavenly new planet. All of this is quite simple and straightforward. So why is the ending such a headscratcher?

What destroyed the Earth in knowing?

The following morning, John decides to visit his family before the flare strikes, and drives through a chaotic Boston to his parents' house, where he reconciles with his estranged father. The solar flare then strikes, destroying the Earth's atmosphere and all life on the planet.