I am looking for (I believe) a short story that involves a robotic ship travelling back in time to destroy the Earth (years before the Terminator stuff). I read the story on the 70s, but it might have been from earlier.
The story has a twist ending in that they are targeting the wrong planet (and the implication is that they kill a planet that is now represented by the asteroid belt).
It definitely sounds like Brian Aldiss' 'T'.
There were several robotic ships travelling back in time to destroy Earth before humans could evolve, each crewed by a single being genetically modified from a captured human. For various reasons the other ships failed e.g. in one the automated system which fed the crew malfunctioned, resulting in excessive growth then death.
Only ship T survived to complete its mission, only to fail as the aliens counted planets inward from outside rather than outward from the Sun, so ended destroying the planet between Mars and Jupiter, forming the asteroid belt
