Arthur C Clarke

For eons, Earth has been under observation by the Firstborn, beings almost as old as the universe itself. The Firstborn are unknown to humankind—until they act. In an instant, Earth's timeline is carved up and reassembled into a patchwork of different eras, from prehistory to the year 2037, each with its own indigenous inhabitants.

Scattered across the planet are floating silver orbs impervious to all weapons and impossible to communicate

...

Returned to the Earth of 2037 by the mysterious and powerful Firstborn, Bisesa Dutt is haunted by memories of her five years spent on the strange alternate Earth called Mir, a jigsaw-puzzle world made up of lands and people cut out of different eras of Earth's history. Why did the Firstborn create Mir? Why was Bisesa taken there and then brought back just a day after her disappearance?

At first, only a few things are known about the celestial object that astronomers dub Rama. It is huge, weighing more than ten trillion tons. And it is hurtling through the solar system at an inconceivable speed. Then a space probe confirms the unthinkable: Rama is no natural object. It is, incredibly, an interstellar spacecraft. Space explorers and planet-bound scientists alike prepare for mankind's first encounter with alien intelligence. It will...