8

I can't find the article, but a mathematician did a calculation on the top five, and they alone produced enough energy to raise the atmospheric temperature by approximately 100 degrees - enough to basically sterilize the planet.

Looking at your list, I think there were only 3 craters larger than 160 km (100 miles). The moon has 60 such craters. The physics favors Earth as a target by at least a factor of 5 just due to the surface area..... leave alone the 6 fold gravitational attraction the Earth has compared to the moon. Based on that, the Earth should have suffered a minimum of 300 such impacts.... about one every 20 years. The impact of a bolide big enough to make a 100 mile smoking hole in the ground is going to be noticed for a very great distance.... and the hole is going to be there a long time.

Using the crater to impactor size calculator at http://www.lpl.arizo...n/crater_p.html with the following parameters:

Crater diameter 160 km (100 miles) Final

Projectile density 1500 kg/m^{3}. This is about the density of an asteroid or comet.

Impact velocity 17 km/sec. Since energy is a function of velocity squared, this will tend to reduce total energy.

Imapct angle 45 degrees.

Target density 3000 kg/m^{3}. Roughly the density of granite.

Acceleration of gravity.... Earth (9.8 m/sec^{2})

Target type component rock or saturated soil.

Result.... impactor size 7450-19200 meters (depending on method of calculation) energy before impact = 2e23 joules (about 47.7 million hydrogen bombs).

The mass of Earth's atmosphere is about 6e24 kg and the specific heat of air is about 1000 j/kg-degree. So, basically 6e27 joules will heat the atmosphere by 1 degree C. At 2e23 joules, this bolide would only add about0.00003 degrees to the atmosphere. As per your citation, the aerosols produced in the blast will cause a cooling effect as they block the sun's energy from reaching the surface.

Of course, nearby it's a scorched Earth. Using the effects calculator at http://impact.ese.ic.../ImpactEffects/ with the same input parameters and 19200 meters for the impactor size,

If you're 800 km (500 mi) from the impact site

at 11 seconds, the fireball will reach maximum intensity. Over the next 40 minutes the average heat energy will be around 164 times what we get from the sun. Clothing will ignite; much of the body will get 3rd degree burns; newspaper ignites; plywood flames; deciduous trees ignite; grass ignites.

At 2.67 minutes the ground waves from the magnitude 10.5 earthquake arrives .... damage is slight.

At 7.24 minutes the ejecta begins to reach your location. You'll end up with about 0.75 m (30 inches) of material with a mean diameter of 4 mm ... about 1/6 inch.

At 40.4 minutes, the air blast hits with a maximum velocity of over 400 m/s .... more than 900 mph.

If that isn't enough, if the impact is in the water, and you're lucky enough to have ocean front property, at about 108 minutes you'll come face-to-face with a tsunami of between 250 and 500 meters.

I think it's safe to say nothing would survive within a radius of 500 miles.

At 1600 km (1000 miles) things are a lot better.)

The fireball is below the horizon, so nothing cooks. The earthquake at 5.33 minutes is noticeable, but does no real damage. The ejecta arriving at 11 minutes is tiny and only accumulates to less than 10 cm (about 3.8 in). The air blast of about 150 m/s (331 mph) that arrives at about 81 minutes might be a problem though. If you're on the beach, the tsunami is down to 125-250 m (400-800 feet). and you have about 2.5 hours before it arrives.

Not much will survive out to a radius of 1000 miles either.....