Such impacts continue to pose a natural hazard to life on Earth. Twice in the twentieth century, large meteorite objects are known to have collided with Earth.
What does this word ''twice " mean in this sentence?
That's exactly what those sentences mean to me. Good job, Running SnailTo owlman5,
Is that the first sentence meaning that there were only two times, while the sencond one means there might be more than two times, but the scientists just have known twice of them?