The Boat Ride
When colonists arrived from Earth, they found a planet so like home they named it Eden One. Orbiting a pale yellow star, the world was situated in the habitable zone where water could exist in all three states and global temperatures, though slightly cooler than at home, were well within the comfort range. Green, wooded, rife with myriads of life-forms very similar to Earth’s, the planet seemed a Paradise in all respects.
What they didn’t know, was that it had a sister-planet with a long eccentric orbit moving through the system like a stalker in the night. Every seven -thousand years, it swept in close enough to wreak catastrophic havoc with the climate, geologic systems and ecologies of both. But life on Eden had evolved to compensate: so when the Burning came, when the ice-caps melted, when the oceans rose to overtake the land, species suited to the Temperate Era metamorphosized or went into a state of hibernation, and another group of species better suited to the new environment, held sway.
This didn’t help the humans who were not adoptable enough to make the change, so Eden was abandoned ~ rather hastily, according to reports.
Robots Tour the Galaxy (again)