How big would an asteroid need to be to revert life to primitive conditions; but not kill everybody on Earth

it would have to be big. like, bigger than the asteroid that killed of the dinosaurs. it would have ot be 15-50 miles in diameter to kill off the major animals but preserve smaller and simpler organisms like bacteria, and extremophiles.

hope this helps! :)
cedric

The "meteor" that just plummeted over Houston, TX a couple of days ago was the size of a basketball. But it looked like a miles long fireball. I don't think it would need to be 15-50 miles in diameter to sent us back to the stone age.

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probably about 10 miles in diameter.

That would send civilization back to the stone age.
Plus it would wipe out most of the human population.
Only people living in certain favorable places would survive, example at high altitude and very far from the impact points.

Tsunamis would drown every one living below about 1000 meters elevation
Plus the dust would cause a permanent winter lasting a year or two world wide. So survivors would need very favorable circumstances not to starve.

And we would not again rise to where we are.
Because we have already used up all of the easily accessible coal and oil supplies.
So we would be back to burning wood.

It doesn't exist. People just aren't going to forget things like electricity. Anything that doesn't wipe out all humanity would only be a temporary setback. Something as deadly as the Black Death in the Middle Ages didn't set back technological progress.

1km .621 miles

10 km (6.2 miles) did it the last time