[johnny7]

Those size asteroids and their blast can be devastaing in a relatively small way.

Once they hit the atmosphere they detonate above ground and flatten what's below.

It's the big boys, thousands of miles in diameter that can snuff out human life on earth.

As of now, we have nothing to stop or deflect these monsters in space.

Food for thought.

[TBall]

"As of now, we have nothing to stop or deflect these monsters in space." I can see it now, we spend tons of money to get a system in place that can deflect the monsters and then a supervolcano goes off and wipes everything out.

[Orangedog]

It's the big boys, thousands of miles in diameter that can snuff out human life on earth.

It wouldn't take anything nearly that large to wipe-out most of the life on the planet. It's believed that the asteroid that killed the dinosaurs (among other things) was about 5 miles in size, impacting and creating what is now the Gulf of Mexico.

Another variable is the makeup of the object. If it's mostly ice (like a small comet) there would be less damage. But if it was comprised of iron, nickle or just plain old rock, then we would have an extinction level event on our hands.

[MeekOneGOP]

Thousands of miles wide? Man! That's like the intruder is the Cue
ball and Earth being the eight ball!

[KarlInOhio]

It's the big boys, thousands of miles in diameter that can snuff out human life on earth.

As of now, we have nothing to stop or deflect these monsters in space.

Aaaiiieeee! They sky is falling.

Let me count the number of asteroids with diameters in the thousands of miles. Hmmm, that would be zero.

Ceres is the largest asteroid, and its diamter is about 600 miles. A NASA site I found had only 7 with diameters above 100 miles, but I don't know if that list was complete.

[DE50AE]

As of now, we have nothing to stop or deflect these monsters in space.

Good point - I think I'm going to run out and buy a hard hat at lunch time today...

[SevenDaysInMay]

"It's the big boys, thousands of miles in diameter that can snuff out human life on earth." Our earth is only about 7,500 miles in diameter.

No, an object only several miles across would create a global catastrophe killing the majority of life forms lasting at least decades, if not centuries. Keep in mind that the deepest ocean abyss is about 6 miles deep; the earth's crust is generally only 25 to 40 miles thick. A high atmosphere "explosion" of a small "rock" would overpressure everything under its entry point as in Siberia. An impact would spray molten ejecta into low orbit altitudes creating a roaring broiler effect over hundreds of thousands of square miles making our current forest fires look like camp fires.
The 65 m.y.o. crater at Yucatan was created by an object only an estimated 6 miles across with geologic evidence indicating a splash's scouring effect to northern Arkansas.
There is strong evidence of several civilization changing events over the last 5,300 years. Either massive volcanoes or small impacts can produce "nuclear winters" chilling global climate for a generation or more.
Just what did trigger ice ages? 3/4 of earth's surface is water.
7 years of food stores is one religion's teachings. From what I remember of the Y2K mania, most humans worldwide have less than 5 days "supply" of food & beverage at emergency rations. Continental scope famine with a million square mile destruction could likely result from a half mile diameter meteorite.