From time to time, life on Earth has endured untold misery. Catastrophic events have wiped out billions of lives from the face of this planet. For some species, these catastrophes meant complete annihilation. For others, only the strongest lived and learned to adapt. The Ordovician-Silurian Mass Extinction is one such event. It is considered to the planet Earth’s second-most devastating extinction event, ranking second after the Great Dying. Let us today learn 25 interesting Ordovician-Silurian Mass Extinction facts and find out what really happened and who suffered.

Interesting Ordovician-Silurian Mass Extinction Facts: 1-13

1. The Ordovician-Silurian Mass Extinction was the second largest mass extinction that took place on earth. The largest was the Great Dying.

2. This event is sometimes referred to as Ordovician Extinction or End-Ordovician Extinction.

3. This extinction event took place during the Hirnantian Age of Ordovician Period and the subsequent Rhuddanian Age of the Silurian Period.

4. The Hirnantian Age lasted from 445.6 m.y.a. to 443.7 m.y.a. while the Rhuddanian Age lasted from 443.7 m.y.a. to 439 m.y.a. Please note that m.y.a. stands for ‘Million Years Ago’.

5. According to experts, this extinction event took place in two phases that were separated by a million years.

6. As far as the severity of the event was concerned, it wiped out over 60% of marine invertebrate life forms. The most interesting thing to know about the Ordovician Period is that there were no land-based animals during that period. All life forms were confined to the oceans.

7. Most badly hit were the bryozoan and brachiopod families. About two-thirds of these families went extinct.

8. In particular, corals, bryozoans, echinoderms, bivalves and brachiopods were most affected.

9. Scientists have for long argued that the mass extinction was caused by an ice age when one of the four supercontinents – Gondwana moved to the South Pole.

10. As large ice sheets formed over the Gondwana, the oceans were drained out of water. Ocean levels dropped by 70 to 100 meters.

11. This fall in ocean levels mostly affected the life forms that lived in shallow waters such as the bryozoans and the corals.

12. The condition lasted for about a million years during which the global temperatures dropped. Life forms that were adapted to warm environmental conditions perished gradually.

13. After 1 million years of ice age came the interglacial period (relatively warmer period with higher global temperatures). It was during this interglacial period that the ice sheets released water.

Interesting Ordovician-Silurian Mass Extinction Facts: 14-25

14. As water was released, sea levels increased and blanketed the shallow marine life forms of the seas. The problem was that the released water was low in oxygen levels and this led to anoxic conditions (oxygen deprived state).

15. Also, the release of water stagnated the deep ocean waters and broke the oceanic circular patterns. This delivered the second phase of extinction.

16. While ice age remains one of the most popularly accepted theories for the Ordovician mass extinction event, there are other theories in place too. One of the popular theories is that a sudden burst of gamma rays triggered the extinction.

17. According to the gamma ray hypothesis, a hypernova sitting some 6,000 light years from Earth sent out a deadly beam of gamma rays which vaporized the 1/3rd of the ozone layer in just 10 seconds, allowing deadly UV radiations of Sun to penetrate the Earth’s atmosphere. Exposure to the UV radiation triggered fatal DNA change in the life forms on Earth.

18. Additionally, scientists propose that the gamma ray burst ripped the oxygen and nitrogen molecules in atmosphere and produced a smog of nitrogen dioxide which blanketed the Earth and effectively blocked the sun rays from penetrating the atmosphere. This led to decline in global temperature and triggered an ice age.

19. The third and new hypothesis blames the mass extinction event on galactic Bow Shock. In simple words, a bow shock forms when material in front of a moving object is compressed. The best example is a moving ship. The water in front of the ship is compressed and a wave is formed which then bends around as the ship moves through.

20. Our Milky Way galaxy also moves very rapidly through space. Thus, it may compress the intergalactic gas in front of it. The compressed gas is heated up and releases cosmic rays. These rays then bend and travel from both sides of the galaxy.

21. The problem with our Solar System is that it actually oscillates through our Milky Way galaxy. This oscillation takes out Solar System above and below the Milky Way’s main disk once in every 64 million years.

22. Once the Solar System manages oscillate out of the protective magnetic field of the galaxy, it becomes exposed to the cosmic rays that are caused by Bow Shock created by Milky Way.

23. Scientists have found from fossil records that the biodiversity of different species increase and decrease in cycles of 62 million years. These cycles closely coincide with Solar System’s cycles of getting exposed to deadly radiations of Bow Shock.

24. Scientists have found that two major mass extinctions occurred when the Solar System was at the highest point of our galactic plane. In other words, these extinctions happened when the Solar System oscillated and moved above the plane of Milky Way and reached beyond the protective magnetic field.

25. So scientists say that it is possible that radiations from galactic Bow Shock could have caused the Ordovician mass extinction with deadly radiations causing DNA damage and genetic mutations that wiped out more than 60% of life forms on Earth.

Sources: 1, 2, 3

Categorized in: