[LRoggy]

It the thing is only 1800 feet wide how could it possibly cause mass extinction??

Oh. Another excuse for a new czar - for Interplanetary Climate Control . . .

[agere_contra]

how could it possibly cause mass extinction??

You're right. It won't.

Depending on where it hit, it might destroy an impressive % of human civilization though.

BUT almost every scenario where a rock manages to smash civilization also predicts San Francisco falling into the sea, so - you know - trade-offs.

[adorno]

It the thing is only 1800 feet wide how could it possibly cause mass extinction??

Just image a bullet traveling at 600 mph. It has been know to kill any living entity that it strikes squarely.

Now, just imagine an 1800 feet wide bullet, but this time traveling at 17,000 or 25,000 mph. Then imagine that bullet striking our dear planet. The point of impact will create a huge crater and the material (ash, dirt, rocks/boulders, heat) from that crater will cover hundreds of miles from the impact point. So, yeah, whatever is within a few hundred miles of impact will either die immediately (around the impact point) or slightly later from the debris raining down in the farther reaches of the affected area. I don't think I'll be around to witness it, but I wouldn't want my descendants (or anybody else) to have to experience it either.

[Lonesome in Massachussets]

It the thing is only 1800 feet wide how could it possibly cause mass extinction??

I don't think you appreciate the amount of kinetic energy that it possesses. An asteriod that size would impart somewhere from 20,000 -40,000 Megatons of energy. It would create a crater tens of miles across and spread debris for thousands of miles. The dust lofted into the atmosphere would darken the sun for months if not years.

Barringer Crater in Arizona (about a mile across) was believed to have been created by an object about ten feet across.

[Minn]

It the thing is only 1800 feet wide how could it possibly cause mass extinction?

Don't watch much Discovery or History Channel, do you?

[jimt]

If the thing is only 1800 feet wide how could it possibly cause mass extinction??

It's called kinetic energy, the energy of a moving mass.

Mathematically it's mass times the velocity squared over two.

Granite weighs about 169 pounds per cubic foot. An 1800 foot diameter sphere contains 3,053,628,059 cubic feet. So the asteroid's weight would be 169 X 3,053,628,059 pounds. Dividing by 32.2 gives us the mass: 1.602681 X 10^10 slugs (mass in the English system).

The speed at impact is estimated to be 42192 feet per second. Squared it's 1,780,164,864. Divided by two it's 890,082,432.

So, multiplying, it's 1.602681 X 10^10 times 8.90082432 X 10^8, or 1.4265 X 10^19 foot pounds.

That equals 4623 megatons of TNT. You saw what 10 kilotons did to Hiroshima. The explosion from the asteroid hitting would be 462,300 times more powerful.