"They also found evidence of the supernova explosion's initial shockwave: 34,000-year-old mammoth tusks that are peppered with tiny impact craters apparently produced by iron-rich grains traveling at an estimated 10,000 kilometers per second. These grains may have been emitted from a supernova that exploded roughly 7,000 years earlier and about 250 light years from Earth.

"Our research indicates that a 10-kilometer-wide comet, which may have been composed from the remnants of a supernova explosion, could have hit North America 13,000 years ago," says Firestone. "This event was preceded by an intense blast of iron-rich grains that impacted the planet roughly 34,000 years ago." "

http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1726

It seems rather unlikely.

But just the other day I was wondering what effect the starship Enterprise would have on Earth if it hit it at light speed.
But anyhow.
Let's check the energy on 10 kilometer wide rock hitting Earth at 10,000 km/sec.
If from a supervova could rock be mostly iron?
And therefore a density of 7 to 8?

Let's say just it was 2 and say it was equal to a sphere
10 km in diameter.
So volume is:
523.6 cubic km or at density of 2: 1047 billion tonne
Or 1.047 x 10^12 kg
Kinetic Energy equals Mass times velocity squared.
Equals 52,350,000,000,000,000,000,000,000 joules
5.2350 x 10^25 joules

2.26 * 10^6 Joules per kg to boil water
10 cubic km of water is 10^13 kgs
So 2.6 * 10^19 joules

So that would only boil 10 million cubic km of water.
Since earth ocean are over 1 billion cubic km of water, they won't completely vaporize. Oh well.
But needless to say, it would leave a mark.

Oh, my mistake. Instead of 1.047 x 10^12 kg, it would
be 1.047 x 10^15 kg. Which makes it 5.2350 x 10^28 joules, and vaporizing 10 billion cubic km of water. So enough energy to vaporize the ocean 7 times over.

I knew there was something wrong.

Of course if the rock had a mass of 1.047 x 10^12 kg- 10 meters diameter, it probably wouldn't kill everything on the planet- nor leave much of a large mark. But it could give the Noah flood, kill everything near it, etc.

Of course we can't really know what any kind rock hitting Earth at 10,000 km/sec would do. I don't think our atmosphere have much affect upon it. I'm not sure the first mile of rock would have much affect upon it. Perhaps fusion reactions would result from it- sort a side affect or accompaniment.

A spitball at that speed would probably be quite impressive.