- See also: Mass Extinction
The causes of three largest mass extinctions in history appear to be evident. Ordovician–Silurian: glaciation. Permian–Triassic: Siberian Traps. Cretaceous–Palaeogene: Chicxulub asteroid impact. The truth is likely much more complex, but new theories are revealing the answers to what really caused a near demise of life on Earth on three occasions.
The diagram to the right will prove very useful to uncovering the complex relationships of mass extinction causes. Two new theories are particularly of interest, the first of which is a gamma ray burst causing the Ordovician–Silurian extinction. While a well-known glaciation is the apparent cause of the second largest extinction of all time, this seems far too benign to wipe out 80% of life on Earth, especially when the glaciation was comparable to late Oligocene temperatures.
Instead, a computer simulation model of a gamma ray burst at Washburn University has shown how a gamma ray burst is not improbable in the span of time provided, how it could easily kill of most life on Earth, and how a minor glaciation could result. A gamma ray burst is a type of supernova in which two streams of gamma rays are shot out of an exploding star in opposite directions at the speed of light, being a type of electromagnetic radiation.
Extreme genetic mutations, acid rain, and ozone depletion all contributed to the killing off of the vast majority of life. The glaciation was a minor result, and contributed in the least to the mass extinction. Furthermore, little data of the glaciation has been collected, and the short duration of the glaciation seems to be the result of an unusual disturbance.
Permian–Triassic and Cretaceous–Palaeogene Extinctions
While the Permian–Triassic and Cretaceous–Palaeogene mass extinctions seem different at first, the resemblance is striking, and enough data has been collected to say that they were both caused by a comet impact causing a large mantle plume to form on the opposite side of the planet and cause basaltic traps. While the Chicxulub impact crater and Siberian Traps have been scientifically proven as causes of the K–Pg and P–T extinctions respectively, they show reverse sides of the catastrophic incident repeated in the two best known mass extinctions.
The Deccan Traps in India have been known for some time as a possible factor in the K–Pg extinction; and more recently, the end Permian aged Wilkes Land crater was discovered in Antarctica; it simply took a while to connect the dots. The final scenario is that a comet smashed into the two locations. It was a comet, and not an asteroid, because the speed of the impact is only great enough to cause the second disaster if it is a comet.
During the Permian, Siberia was opposite of Antarctica; the same is true of Cretaceous India and Mexico. Each comet impact caused a rising mantle plume, resulting in the Siberian and Deccan Traps, and the last phase of the extinction. Therefore, the exact same scenario is responsible for the largest extinction of all time and the one which wiped out the dinosaurs.
As we continue to learn new information, our views will further change on the demise of past life. For now, though, these are plausible theories to the causes of major extinction events.