Space Invader: The Big Bopper

The biggest catastrophe in the history of advanced life on this planet was a pretty big one indeed. The Permian-Triassic extinction event killed off 90% of marine species (including the last trilobites) and 70% of terrestial vertebrate species, and very likely, almost every individual creature alive. There have a number of theories as to the cause (Wiki link) but a relatively new one is based on the discovery of the remains of an "Ohio sized"crater under the Antarctic ice.

The crater, buried beneath a half-mile of ice and discovered by some serious airborne and satellite sleuthing, is more than twice as big as the one involved in the demise of the dinosaurs.

The crater's location, in the Wilkes Land region of East Antarctica, south of Australia, suggests it might have instigated the breakup of the so-called Gondwana supercontinent, which pushed Australia northward, the researchers said.

"This Wilkes Land impact is much bigger than the impact that killed the dinosaurs, and probably would have caused catastrophic damage at the time," said Ralph von Frese, a professor of geological sciences at Ohio State University.

Meanwhile, it seems that the University of Arizona's Lunar and Planetary Lab has produced a handy dandy on-line Earth Impacts Calculator. I tried checking it out by plunking down a suitable asteroid and watching it from a couple of thousand kilometers away (near Australia?). Here is it's diagnosis:

Your Inputs:
Distance from Impact: 2000.00 km = 1242.00 miles
Projectile Diameter: 50000.00 m = 164000.00 ft = 31.05 miles
Projectile Density: 3000 kg/m3
Impact Velocity: 20.00 km/s = 12.42 miles/s
Impact Angle: 45 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock
Energy:
Energy before atmospheric entry: 3.93 x 1025 Joules = 9.38 x 109 MegaTons TNT
The average interval between impacts of this size is longer than the Earth's age.
Such impacts could only occur during the accumulation of the Earth, between 4.5 and 4 billion years ago.
Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.
Crater Dimensions:

Transient Crater Diameter: 240 km = 149 miles
Transient Crater Depth: 85 km = 52.8 miles

Final Crater Diameter: 493 km = 306 miles
Final Crater Depth: 1.91 km = 1.19 miles
The crater formed is a complex crater.
The volume of the target melted or vaporized is 247000 km3 = 59300 miles3
Roughly half the melt remains in the crater , where its average thickness is 5.45 km = 3.38 miles
Thermal Radiation:

Time for maximum radiation: 34 seconds after impact

Visible fireball radius: 368 km = 229 miles
The fireball appears 41.9 times larger than the sun
Thermal Exposure: 2.05 x 109 Joules/m2
Duration of Irradiation: 8830 seconds
Radiant flux (relative to the sun): 232


Effects of Thermal Radiation:


Clothing ignites

Much of the body suffers third degree burns

Newspaper ignites

Plywood flames

Deciduous trees ignite

Grass ignites

Seismic Effects:

The major seismic shaking will arrive at approximately 400 seconds.
Richter Scale Magnitude: 11.3 (This is greater than any earthquake in recorded history)
Mercalli Scale Intensity at a distance of 2000 km:


VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.

VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.


Ejecta:

The ejecta will arrive approximately 764 seconds after the impact.
Average Ejecta Thickness: 3.72 m = 12.2 ft
Mean Fragment Diameter: 1.25 mm = 0.0491 inches


Air Blast:
What does this mean?


The air blast will arrive at approximately 6060 seconds.
Peak Overpressure: 793000 Pa = 7.93 bars = 113 psi
Max wind velocity: 669 m/s = 1500 mph
Sound Intensity: 118 dB (May cause ear pain)
Damage Description:


Multistory wall-bearing buildings will collapse.

Wood frame buildings will almost completely collapse.

Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse.

Highway truss bridges will collapse.

Highway girder bridges will collapse.

Glass windows will shatter.

Cars and trucks will be largely displaced and grossly distorted and will require rebuilding before use.

Up to 90 percent of trees blown down; remainder stripped of branches and leaves.

This is cool, but I think the event might have saturated its effects calculator. "Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse...Up to 90 percent of trees blown down; remainder stripped of branches and leaves" in a 1500 mi/hr wind? I don't think so. 100 percent of trees would be converted to wood dust, and steel office type buildings would be blasted to bits.

"Clothing ignites

Much of the body suffers third degree burns." I think they mean vaporizes.

I got the same effects even when I cranked up the speed enough to put my observer inside the fireball.