They estimate that it is likely the impact was less than 3 million years ago, though perhaps only 12,000 years ago. This may have interfered with humanity's development.
And these things are travelling on average at 30,000 mph. That's so fast the human eye would not even pick it up if it sped by at ground level. Tough to imagine the energy produced at ground zero. A chunk of rock a kilometer wide travelling 30,000 mph coming to a dead stop. The energy from that would literally vaporize anything standing within a hundred mile radius of the impact point, at least.
