Of all mass extinction events that have ever occurred on Earth, the Great Dying was THE MOST DEVASTATING one but, the Cretaceous-Tertiary extinction event is THE MOST FAMOUS extinction event. Why? Because this extinction event that happened 66 million years ago, ended once and for all, the rule of the dinosaurs on planet Earth and cleared the way for human evolution. So, let us learn 30 interesting Cretaceous-Tertiary extinction event facts and find out what really happened that brought an end to the likes of T-Rex and other massive dinosaurs that breathe fear in us even today!
Interesting Cretaceous–Tertiary Extinction Event Facts: 1-10
1. The Cretaceous-Tertiary extinction event (abbreviated as K-T extinction) is also known as the Cretaceous-Paleogene extinction event (abbreviated as K-Pg extinction).
2. This event was responsible for wiping out 3/4th of all animal and plant species that lived on Earth during that period.
3. This extinction event marked the end of the Cretaceous period and the Mesozoic Era. After the Mesozoic Era ended, the Cenozoic Era began which continues till date.
4. The most famous of all animals that lived during the period were the dinosaurs. The event wiped out all non-avian dinosaurs completely.
5. The dinosaurs had already lived for 165 million years with several species evolving and dying out but by the time of this event, the whole of dinosaur species was already struggling with survival and the event was the straw that finally broke the camel’s back, putting an end to their misery.
6. Though we most often restrict our attention to dinosaurs, the K-T extinction killed several other animal and plant species.
7. The gargantuan Plesiosaurs and Mosasaurs in seas, the last of Pterosaurs in sky, many sea sponges and brachiopods, the last of the hard-shelled ammonites were completely obliterated.
8. Here is a quick list of what was destroyed and what was left:
- Archosaurs (from which modern crocodilians and birds evolved) survived and rest of all dinosaurs perished.
- 13% of planktonic foraminiferal and coccolithopore genera lived. Every other planktonic flora and fauna of marine world was annihilated.
- Belemnoids and ammonoids among the free-swimming mollusks were obliterated completely.
- Inoceramids which were strategically important during the period were also wiped out completely.
- Only 1/5th of hermatypic corals survived.
9. The K-T extinction has an interesting aspect. The impact of the event differed on different life forms. For example, land-based plants survived better than land-based animals despite the fact that several plant species were completely obliterated.
10. Certain reptilian groups like snakes, lizards, crocodilians and turtles were not affected or very slightly affected. Some mammals and amphibians also had mild impact.
Interesting Cretaceous–Tertiary Extinction Event Facts: 11-20
11. Whatever happened, the Cretaceous-Tertiary extinction event was the third deadliest extinction event in history of Earth with first position taken by Great Dying and second position captured by Ordovician-Silurian mass extinction event.
12. What really happened? There are many theories that attempt to explain the K-T extinction. Even today, nearly 2 centuries after the hunt for causes started, scientists hold different views. Some proposed hypotheses include:
- A supernova explosion sending out gamma rays that led to extinction.
- Egg-eating mammals increased and this led to collapse of other animals.
- Spells of freezing cold killed animals and plants.
- Heat waves that resulted in sterility.
- Widespread disease.
13. Of course, none of them are really credible enough to explain the third-largest mass extinction! In 1980’s however, a new theory was proposed – ‘a huge stone from space slammed on earth’.
14. According the asteroid theory proposed by American scientists Walter and Luis Alvarez, a comet or a meteorite slammed on earth and the resulting force sent a huge amount of dust and rock debris hurdling up into the atmosphere. The sheer volume of the debris allowed it to cover the whole of earth and keep it in darkness for several months and possibly more.
15. The resulting darkness prevented photosynthesis in plants and wiped out several plant species. This in turn disrupted the whole food chain and resulted in mass extinction.
16. There are plenty of evidence found in rock records that support the asteroid there. The most famous of all records ever found was the discovery of a crater beneath Yucatan Peninsula sediments near Chicxulub, Mexico. This crater belonged to the latest Cretaceous and is 180 kilometers in diameter.
17. Apart from this iridium, which is a rare-earth metal usually found deep in the mantle of Earth and more commonly found in extraterrestrial rocks, has been found in several deposits which are associated with the extinction event. This suggests that iridium in those deposits were caused by an asteroid impact.
18. Other evidences include discovery of tektites, which are nothing but fractured sand grains caused by an impact of a meteorite. Also evidences of gigantic tsunami washing up the shores of Gulf of Mexico suggest an asteroid impact that triggered the extinction.
19. Also, scientists think that the asteroid impact managed to inject sulfuric acid aerosols into stratosphere that blocked sunlight penetration by about 20%. These aerosols took at least a decade’s time to dissipate, which was enough time to kill many species of flora and the dependent fauna that included both herbivores and carnivores.
20. Also, scientists found evidence that the whole of terrestrial biosphere was torched because of the falling incendiary debris. The intense fire was supported by high oxygen levels in the late Cretaceous.
Interesting Cretaceous–Tertiary Extinction Event Facts: 21-30
21. This intense combustion led to high CO2 levels atmosphere and once the debris settled, the CO2 resulted in a temporary greenhouse effect in early Cenozoic era which eventually killed the surviving but vulnerable organisms after the asteroid impact.
22. While the asteroid theory is extremely strong with huge number of supporting evidences, some scientists argue that the rock alone could not have been a force powerful enough to trigger K-T extinction.
23. Some experts have proposed that during the late Cretaceous, massive volcanic activities were responsible for gradual extinction. They blame the Deccan Traps flood basalt (in India) was the reason for extinction.
24. According to experts, the Deccan Traps event started some 68 million years ago and continued for 2 million years or more. Modern research indicates that the traps erupted for a period of 800,000 years in K-T boundary. Thus, it might have been responsible for the 3rd largest extinction event and also delayed biotic recovery after the extinction event. The results of the volcanic activities theory are similar to that of the Great Dying.
25. The other popular theory is that of multiple impacts. Though not much different from the asteroid theory, this one deviates in the fact that it was not one rock that caused the extinction. In fact, it was a series of extraterrestrial rocks that led to extinction.
26. Multiple other craters have been found from late Cretaceous. For instance one crater was found in 2002 in Boltysh, Ukraine. This crater predated the Chicxulub crater by 2,000 to 5,000 years. Again, there was Silverpit crater in North Sea and also the controversial Shiva crater in India. The Shiva crater has a teardrop shape and is 600 kilometers long and 400 kilometers wide.
27. Drop in sea levels in another theory that has been linked to the Cretaceous-Tertiary extinction event. There are very valid evidences of severe regression (drop) of sea levels but scientists are not sure of what caused such massive drop.
28. According to this theory, the sea level dropped so significantly that the continental shelf area was reduced dramatically. Today we know that continental shelf is THE MOST species-rich area in any sea.
29. According to experts, this massive regression led to extinction of many marine life forms. They also suggest that the drop in sea level caused changes in ocean currents and disrupted winds that led to catastrophic climatic changes.
30. Also, drop in sea levels reduced the reflecting power of Earth which in turn caused more and more heat to get trapped in and thus, led to global temperature rise. This is turn led to extinction of several species of animals and plants.