A verneshot is a hypothetical volcanic eruption event which launches an extremely large rock into a sub-orbital trajectory. According to the Department of Marine Geodynamics at GeoMar, Kiel, such an event could be triggered by an explosion caused by a mantle plume under a craton in an area of continental rift . Verneshots are one possible cause for extinction-level events.

The four major mass-extinctions that may have been caused by verneshots are:

• the Frasnian-Fammian extinction event 364 million years ago, killing off 70% of all marine life, linked to the Siljan crater in Sweden and the Pripyat-Dniepr-Donetsk supervolcano in the Ukraine
• the Permian-Triassic extinction event 251 million years ago, killing off 96% of all life on the planet, linked to the Bedout submarine potential impact crater off the coast of Australia and the supervolcano forming the Siberian Traps
• the Triassic-Jurassic extinction event 200 million years ago, killing off 20% of species, linked to the Manicougan crater in Canada and the Central Atlantic Magmatic Province supervolcano off the coast of Sierra Leone
• the Cretaceous-Tertiary extinction event 65 million years ago, killing off 60% of species, linked to the Chicxulub crater in Mexico and the Deccan Traps supervolcano in India

With these four events, massive volcanic activity over thousands of square miles coincides with an impact event. The verneshot theory is that gas seeps up deep underground in an upwelling of magma like the hotspot which formed Hawaii but on a much larger scale. It is trapped beneath impenetrable rock known as a craton (continental plate rock). As pressure builds up, the gas cracks the craton and blasts out at immense velocity. This gas would poison the atmosphere and cause a massive earthquake, enough to level mountain ranges.

The pipe through which the magma and gas had travelled is now empty and collapses. A shockwave at hypersonic velocity would hit the remains of the craton and pulverise them with an explosion equivalent to 120 gigatons of TNT. Twenty billion tons of debris is blasted into the atmosphere while lava fills the hole left behind. The verneshot impactor (the largest lump hurled out) then impacts earth elsewhere. The Chicxulub crater is consistent with such an event with the direction and low angle of impact. However, the velocity would be low compared to an extraterrestrial impactor, so the impactor would mostly survive and although it would be pulverised, it would not be vaporised. Finding rocks from Deccan in Mexico would validate this theory.

What this theory doesn't explain:

• The impact events are associated with layers of extraterrestrial material, such as the iridium of the KT event. This would need to be present in earth's mantle and there is little evidence to support that.
• The impacts are too small; a verneshot would generate an impactor over a hundred miles across, not the ten mile things that bring about mass extinctions. In short, Chicxulub would be larger than the continental United States if caused by a verneshot.
• A verneshot could result in smaller impacts, but there'd be dozens of them. We don't see this. Revision of the scale of the verneshot theory may be necessary.