Counterblow in Earth?

 kw: physical phenomena, seismic focusing, extinctions, asteroid impacts, flood volcanism, siberian traps, deccan traps

A YouTube video from Demolition Ranch features a large glass sphere, eight or nine inches in diameter, which was shot at with various guns. A very interesting phenomenon occurred with each shot, from 9mm and larger.

Near the left side of the sphere is the damage at the impact site from a .44 Magnum round. The damage covers about 1/4 of the surface of the ball, and conchoidal fractures are seen inside the ball all around it. The damaged area right of center is from an earlier shot with a smaller caliber round.

The amazing phenomenon appears when the sphere is turned around…

At lower left, there is a zone of damage, a shattered area surrounded by conchoidal fractures. Through the sphere you can see, at upper right, the larger damaged area around the impact. Two other bullets of lesser caliber also caused damage on the side of the sphere opposite their own impact points.

What has happened here? Some very interesting physics!

The concussion wave from the bullet impact was focused by the ball on the area opposite the impact, where it was powerful enough to do significant damage. This has implications for events in Earth's history that I have thought about over several decades.

As a geology student in the early 1970's I learned of the "large igneous provinces", characterized by enormous quantities of flood basalt. Two in particular stand out: the Siberian Traps and the Deccan Traps. In geology, a "trap" is a stepped area underlain by a large sheet of igneous rock such as a flood basalt. The word "trap" comes from a Swedish word for "staircase".

These two igneous provinces have ages that coincide with two of the great extinction events. The Siberian Traps were emplaced about 251 million years ago, and are considered the primary cause of the great end-Permian extinction event, when 90% of all species were exterminated, and about 99% of all animals and plants were killed. 

The Deccan Traps of western India were emplaced about 65 million years ago, and have been proposed as either a primary cause or a strong contributing factor to the great end-Cretaceous extinction event, when 75% of all species were exterminated, and about 90% of all animals and plants were killed, including nearly all the dinosaurs (the surviving, smaller dinosaurs later became birds). This article in Science Direct, from 1999, reports on the age of the Deccan Traps: 65.6±0.3 million years.

You probably know that an asteroid some 10 km in diameter is known to have struck near what is Yucatan today, 65 million years ago, and is now considered the primary cause of the "Doom to Dinosaurs" extinction.

Is it just a coincidence that enormous volcanic eruptions in India began just then? I think not. Paleogeography is not yet as exact as I would like. Continental motions are known in general terms, but not with great accuracy. As well as I can determine, though, Yucatan and India were antipodal to one another 65 million years ago. I think it is likely that the impact triggered the volcanism, by the same focusing mechanism that the glass sphere experienced. The amount of lava that erupted is hard to conceive: about a million cubic km, covering an area of half a million square km to a depth of 2 km. The volcanism went on for about 30,000 years (that word "about" is very iffy!).

Thus, as bad as the "nuclear winter" caused by the asteroid impact would have been, the volcanism made things a great deal worse. Without the Trap basalt eruptions, the extinction event might have been much less severe.

Now, consider the Siberian Traps. The volume of erupted material is 4 million cubic km, and covers an area of 7 million square km. That's whole lot bigger and badder. All by itself, this is considered quite sufficient to have caused the end-Permian extinction.

Could the Siberian Trap volcanism also have been triggered by an antipodal asteroid strike? The arrangement of continents 251 million years ago is even less precisely known, compared to 65 million years ago. I looked at reconstructions of Pangea at about that time. It appears that the point antipodal to the middle of the Siberian Traps was in the ocean, 1,000-2,000 km off Antarctica (which was 30 degrees north of the South Pole at that time).

Had the antipode of north-central Siberia been on a continent, it would be worthwhile to look for a long-buried crater some 400 km in diameter (or larger). However, the ocean floor is consumed at a steady rate by plate tectonics. There is hardly any ocean floor now existing that is older than 200 million years, and that is an edge of the Pacific plate west of Alaska. There is little to no likelihood that a crater remnant from an asteroid, that could have triggered the Siberian Trap volcanism, will ever be found.

While I think it likely that an asteroid triggered the Siberian flood volcanism, I can't prove it. But the experiments with the glass sphere are certainly suggestive!