Today marks the 100th anniversary of the Tunguska explosion.

...just thought you'd like to know.

Good link here: Science News - Tunguska, A Century Later

Wikipedia link: Tunguska event

Testimony of S. Semenov, as recorded by Leonid Kulik's expedition in 1930.[9]
"At breakfast time I was sitting by the house at Vanavara trading post (65 kilometres/40 miles south of the explosion), facing North. [...] I suddenly saw that directly to the North, over Onkoul's Tunguska road, the sky split in two and fire appeared high and wide over the forest (as Semenov showed, about 50 degrees up - expedition note). The split in the sky grew larger, and the entire Northern side was covered with fire. At that moment I became so hot that I couldn't bear it, as if my shirt was on fire; from the northern side, where the fire was, came strong heat. I wanted to tear off my shirt and throw it down, but then the sky shut closed, and a strong thump sounded, and I was thrown a few yards. I lost my senses for a moment, but then my wife ran out and led me to the house. After that such noise came, as if rocks were falling or cannons were firing, the earth shook, and when I was on the ground, I pressed my head down, fearing rocks would smash it. When the sky opened up, hot wind raced between the houses, like from cannons, which left traces in the ground like pathways, and it damaged some crops. Later we saw that many windows were shattered, and in the barn a part of the iron lock snapped."

Would you like to see the size of an impact crater depending on the size and make-up of an asteroid?

Yes?

I knew you would.  Go over here and check it out: [Impact Calculator]

An interesting read here from Gregg Easterbrook regarding the risks from a major asteroid strike on the Earth.  Once thought to be a terribly remote occurrence, it seems the more the astronomers look at the issue the less rare it appears to be.

The Sky Is Falling

A generation ago, the standard assumption was that a dangerous object would strike Earth perhaps once in a million years. By the mid-1990s, researchers began to say that the threat was greater: perhaps a strike every 300,000 years. This winter, I asked William Ailor, an asteroid specialist at The Aerospace Corporation, a think tank for the Air Force, what he thought the risk was. Ailor’s answer: a one-in-10 chance per century of a dangerous space-object strike.

Although from what I can glean from this table: Sentry Risk Table [NASA], there appears to be only one rock that is of any concern at this time. [this one - 2007 VK184] and that will happen June 3rd...2048.

The whole point of the first article seems to be that we may be more at risk than we had previously thought and spending some money on asteroid defense systems may be prudent.