The consensus among scientists who support this theory is that the impact caused extinctions both directly, by heat from the meteorite impact (which could have also triggered global firestorms as incendiary fragments from the blast fell back to earth) and mega-tsunamis, and also indirectly via a worldwide cooling brought about when matter ejected from the impact reflected thermal radiation from the sun. This would have blocked sunlight and inhibited photosynthesis, and accounted for the extinction of plants and organisms. In 1990, scientists confirmed that that an asteroid, 15 kilometers wide must have hit in the vicinity of the Yucatan Peninsula (in southeastern Mexico), creating the approximately 180 km wide and 10 km deep Chicxulub Crater, triggering the mass extinction. At the time of the impact, the asteroid was travelling at nearly 70,000 miles hour (roughly 20 times the speed of a rifle bullet), and the impact released about a billion times more energy than the atomic bombs dropped on Hiroshima and a million times larger than the largest nuclear bomb ever tested. According to scientists of the Imperial College of London, the impact would have triggered massive earthquakes, landslides, continental shelf collapses and mega-tsunamis, as well as a global winter, which wiped out much of life on Earth in a matter of days.

The multiple impact theory suggests the possibility of near simultaneous multiple impacts, possibly from a fragmented asteroidal object. This is supported by the discovery of several other craters, which appear to have been formed at the K–T boundary. Among these are the Boltysh crater, a 24 km diameter impact crater in Ukraine; and the Silverpit crater, a 20 km diameter impact crater in the North Sea. Recently, another major impact structure, the Shiva Crater, has been identified at the India-Seychelles plate margin, in the Indian Ocean to the west of Mumbai, almost antipodal to the Chicxulub structure. In a paper published in 1997, paleontologist Sankar Chatterjee writes:

“This buried oblong crater is 600 km long, 450 km wide and 12 km deep and may represent the largest impact structure of Phanerozoic age. The KT boundary age of the crater is inferred from its Deccan lava floor, Paleocene age of the overlying sediments, isotope dating (~ 65 Ma) of presumed melt rocks, and the Carlsberg rifting event that split the crater into two halves…It is estimated that a 40-km diameter meteorite crashed on the western continental shelf of India around 65 Ma, excavating the Shiva Crater, shattering the lithosphere, and triggering the India-Seychelles rifting.”

Fig 4: The Barringer Meteor Crater in Arizona, 1.2 km wide, 170 m deep. It was created nearly 50,000 years ago by a small meteorite about 50 meters across, which released about 10 megatons of energy. In contrast, the asteroid that created the 180 km wide Chicxulub Crater in Mexico released about 100 million megatons of energy. Source: U.S. Geological Survey

Another important discovery in this regard was made independently by Alvarez and Muller, and by Rampino and Stothers, and subsequently validated by Shoemaker, which showed that the impact craters on earth had a periodicity of either 28.4 or 30 Myr, which matches the periodicity of mass extinctions. This suggested that the impact craters must have been created during ‘comet showers’ or ‘storms’ – a large number of impacts over a relatively short period of time.

Subsequently, two teams of astronomers, Whitmire and Jackson, and Davis, Hut, and Muller, independently published similar hypotheses to explain Raup and Sepkoski's extinction periodicity in the same issue of the journal Nature. This hypothesis proposes that the Sun may have an as yet undetected companion star in a highly elliptical orbit that periodically disturbs comets in the spherical Oort cloud that surrounds our Solar System, causing a large increase in the number of comets visiting the inner Solar System, with a consequential increase in impact events on Earth. This became known as the Nemesis hypothesis. If Nemesis does exist, its exact nature is uncertain. Richard A. Muller suggests that the most likely object is a red dwarf star with magnitude between 7 and 12. He also states that if the last comet shower was 13 Myr ago, then Nemesis would be at its greatest distance, about 3 light-years; if the shower was 5 Myr ago, then Nemesis would be only half that distance.  

However, a binary companion of the sun has not been found till date, in spite of extensive sky surveys. It has been noted by many scientists that the orbit required for a 26 to 30 million years period is unstable against perturbations from passing stars and molecular clouds. Thus, it is extremely unlikely that the proposed companion star has been in this orbit for the past 250 million years, and hence it cannot account for the 26 million year periodicity in impact events. However, supporters of this hypothesis are still hoping that the WISE mission (an infrared sky survey that covered most of our solar neighborhood in movement-verifying parallax measurements) will be able to be able to find it, if it exists. Preliminary results of the WISE survey were released on 14 April 2011. The final release of analyzed results is scheduled to be released in March 2012.  It would be fair to say, though, that the Nemesis hypothesis has lost credibility within the scientific community.

The explanations for the mass extinction events provided in the ancient texts have been couched in mysterious symbolisms that have been impossible to decode. The Mahabharata tells us that “a fire from the mouth of the underground serpent will burn the lower worlds, then the surface of the earth, and will set the atmosphere ablaze. This mass of fire will burn with a great noise. Surrounded by these circles of fire, all animate and inanimate objects will be destroyed.” Similar accounts have been preserved by the Nordic people of Ragnarok, the final destruction of the world. The event states that during Ragnarok, Jörmungandr, the Midgard serpent, will rise from the deep ocean bed to proceed towards the land, twisting and writhing in fury on his way, causing the seas to rear up and lash against the land. With every breath, the serpent will spew venom, staining the earth and the sky in poison. Some of the catastrophes that occurred during the last time the universe was dissolved are still remembered and recounted: The ash tree Yggdrasil was shaken from its roots to its topmost branches. The Earth itself was beginning to lose its shape. The stars were coming adrift from the sky and falling into the gaping void. The giant Sun set the entire earth on fire; the universe was no longer more than an immense furnace. All living things, all plant life, were blotted out. All that remained was the soil.

These descriptions seem to suggest a cosmic catastrophe of unimaginable proportions. But the exact nature of this phenomenon still eludes us. Are these descriptions hinting at a ‘galactic core explosion’? We know that the Milky Way galaxy is a ‘Seyfert’ galaxy, which periodically has highly energetic explosions taking place in its core that result in the ejection of huge amount of cosmic debris including stars, dust and cosmic ray particles. Astronomers speculate that this kind of explosive activities may occur as infrequently as once in every 10 to 100 million years, which falls pretty much in the range of the 26 million year mass extinction events. Once the core becomes explosive, the galaxy remains in that explosive stage for a few million years, and then becomes quiescent, before erupting again. Scientists believe that interstellar magnetic fields in the galactic nucleus will trap the emitted particles in spiral orbits causing them to reach the earth very slowly, and thereby not pose any grave threat to the earth. However, Paul LaViolette, the author of Earth Under Fire is of the opinion that “cosmic ray electrons and positrons generated in a core explosion travel radially outward from the Galactic Center at very close to the speed of light and pass through the entire galactic disk with minimal attenuation” , and bombard solar systems like our own residing in its spiral arm disk. These emitted cosmic rays travel radially outward “in the form of an expanding spherical shell that has a thickness of several hundred to several thousand light years”. Such an explosive event can cause substantial damage to life on earth, and may be responsible for the periodic cataclysms that impact our planet.

It is possible, therefore, that the ancient myths may be hinting at a cyclical ‘galactic core explosion’ that takes place every 26 million years. However, such a hypothesis requires much more analysis. What is certain, however, is this: the ancients were aware of the mass extinction events that are recorded in the fossil history of the earth, as well as the cosmic phenomenon that triggers these periodic catastrophic destructions. And this information has been transmitted down to us for uncounted millennia, couched in various mysterious symbols, myths and metaphors. It is now up to us to decode this information.

• Surya-Siddhanta:a text-book of Hindu astronomy, Ebenezer Burgess, Phanindralal Gangooly, Chapter 1, p 1

• The Bhagavad Gita 8.17-8.20

• Raup and Sepkoski, Proc. Natl. Acad. Sci. USA, Vol 81, pp 801-805, February 1984

• Sankar Chatterjee, Proc. 30th Intern. Geol. Congr., Vol 26, pp 31-54, 1997

• Whitmire, D.P.; Jackson, A.A. (1984). "Are periodic mass extinctions driven by a distant solar companion?", Nature 308 (5961): 713–715.

• Davis, M.; Hut, P., Muller, R.A. (1984). "Extinction of species by periodic comet showers". Nature 308 (5961): 715–717.

• Muller, R.A. (1985). “Evidence for Nemesis: A Solar Companion Star”. LBL, University of California.

• Paul LaViolette, Earth Under Fire, p 67, Bear & Company, 2005