Thousands of Potentially Hazardous Asteroids intersect Earth Orbit

Timothy Birdnow

NASA, ever eager to spread apocalyptic news, has calculated the number of potentially hazardous asteroids (PHA's), asteroids that intersect the Earth's orbit, at 4.700, give or take 1,500.
http://science.nasa.gov/science-news/science-at-nasa/2012/16may_pha/

According to the article:

"The asteroid-hunting portion of the WISE mission, called NEOWISE, sampled 107 PHAs to make predictions about the population as a whole. Findings indicate there are roughly 4,700 PHAs, plus or minus 1,500, with diameters larger than 330 feet (about 100 meters). So far, an estimated 20 to 30 percent of these objects have been found.

While previous estimates of PHAs predicted similar numbers, they were rough approximations. NEOWISE has generated a more credible estimate of the objects' total numbers and sizes. Because the WISE space telescope detected the infrared light, or heat, of asteroids, it was able to pick up both light and dark objects, resulting in a more representative look at the entire population."

End excerpt.

Beyond a certain size the Earth's atmosphere makes no difference on an asteroid; even if a sizable chunk is turned to plasma that energy is coming with the rest of the body. At the speeds these objects move they just aren't in the atmosphere long enough to burn up. How much of a 500 foot long asteroid can vaporize in one second? 

Asteroid strikes leave circular craters; take a look at the Moon and Mars. It is interesting to note how many unusually large, round spaces are visible on the Earth; Yucatan, Hudson Bay, the Persian Gulf, the Black Sea, etc. How many are the result of asteroid strikes?

Luis Alvarez, scientist with the Manhattan Project and Nobel Laureate, and his son Walter developed the theory that the dinosaurs were killed by an asteroid strike in Yucatan. They noticed there was a layer of irridium in the soil that appears at the K-T Boundary (the end of the Cretaceous), and this iridium suggested an asteroid slammed into the Earth, blotting out the sun and likely killing most species on the planet. Thus was born the most widely held view of what killed the dinosaurs.

So, it may be that we have been getting clunked by these things for a long time. Perhaps Mankind owes it's very existence on this planet to an asteroid strike? 

One thing is obvious; we are an extraordinarily lucky species. I would argue that we owe it all to divine intervention, and we should be grateful lest a hailstorm of extraterrestrial stones fall upon our heads.

But we are an ungrateful lot, and will no doubt continue to believe we owe it all to our own spunk and talent.

But given enough time any event is likely to occur, and the chances of getting creamed by one of these things is a certainty; the question is when. There isn't a whole lot we can do about it now.

That could change, but it requires a permanent human presence in space. We could move these things if we have the hardware up there, which means we need to use the space program for more than Muslim outreach. We need to build a serious infrastructure in Earth orbit, and we need to build permanent facilities to mine the Moon for our raw materials. Mankind cannot turn it's back on space. Time is not on our side.