New Life for Shiva Hypothesis

For decades, scientists have argued about a controversial hypothesis, relating to periodic mass extinctions and impact craters, caused by comet and asteroid showers on Earth. This became known as the "Shiva-hypothesis," after the Hindu god of creation and destruction.

Our solar system is thought to orbit the center of the Milky Way once about every 250 million years. As it journeys through this vast cosmic year, our Sun and solar system also move up and down through the crowded galactic disk, in a cyclical weaving motion that lasts about 30 million years.

New York University Biology Professor Michael Rampino noted as early as 1984 that the pattern of the Earth’s oscillating motion through the galactic disk seems to correlate with mass extinctions, the most famous of which took place about 66 million years ago, wiping out the dinosaurs. In a new paper, Rampino concludes that movement through dark matter may perturb the orbits of comets and lead to additional heating in the Earth’s core, both of which could be connected with mass extinction events.

Six mass extinctions during the studied period correlate with times of enhanced impact cratering on Earth. Moreover, five out of the six largest impact craters of the last 260 million years on Earth correlate with mass extinction events. One of the most extraordinary craters, even by mass-extinction standards, is the large, 180 kilometre, Chicxulub impact structure in the Yucatan, which dates to about 65 million years ago, the time of the great mass extinction that included the dinosaurs. The city-sized asteroid that created Chicxulub released more energy than 1 billion nuclear bombs when it hit the Earth and also set off a global chain-reaction of volcanic eruptions.

Recognition of this 30 million year Galactic cycle is the key to understanding why extinctions happen on a regular schedule, but it may also explain other geologic phenomena as well. A number of geological events, including pulses of volcanic eruptions, mountain building, magnetic field reversals, climate and major changes in sea level, all show a similar 30 million year cycle.

A possible cause of geological activity may be interactions of the Earth with dark matter in the Galaxy. Dark matter, which got its name because it has never been seen, is most likely composed of tiny sub-atomic particles that reveal their presence solely by their gravitational pull. As the Earth passes through the Galaxy’s disc, it may encounter dense clumps of dark matter.

Physicists have argued that the dark matter particles can be captured by the Earth, and will build up in the Earth’s core. If the dark matter density is great enough, the dark matter particles eventually annihilate one another, adding a large amount of internal heat to the Earth that can drive global pulses of geologic activity.

If dark matter is concentrated in the flat Galactic disc of stars, gas and dust, measuring some 120.000 light-years across, geologic activity should show the same 30 million year cycle. Thus, the evidence from the Earth’s geological history supports a picture in which astrophysical phenomena govern the Earth’s geological and biological evolution.

If the hypothesis is correct, the next mass extinction may not be far off, in geologic terms, anyway. Our solar system crossed the plane about 2 million years ago, and we are now moving up and through it. We are still close to the plane, maybe 30 light years above it, and have been in the danger zone for a couple of million years, but we won’t come back across the plane for about another 30 million years.

That doesn't mean nothing could happen. Around the end of the Ice Age, only 12.900 years ago, an extreme and sudden drop of global temperatures caused by the impact of a large comet marked the beginning of the 1200-year geological era of the Younger Dryas, one of the most well-known examples of abrupt climate change.

Fortunately, scientists are actively scouring the skies, and calculating the orbits of monstrous comets and asteroids. Once we know one is coming, then there are several options to divert the object. You don’t want to blow a comet up, because that would just increase the numbers of impactors. One possibility is to push, or even gravitationally pull, the comet or asteroid just slightly off course. Possibly just hitting the object with a rapidly moving space-craft would provide enough of a nudge.

There might be one silver lining though: The impacts may have thrown debris containing micro-organisms out into space and across the universe and helped life spread across the galaxy.