The Great Dying: How the Dinosaurs Had It Easy
Long ago, an asteroid caused the most well-known mass extinction.
Image courtesy of Don Davis via Wikimedia Commons
More than 65 million years ago, the sky rumbled. Some dinosaurs in present-day Mexico may have briefly tried to run before they were instantly vaporised by the impact of a 15km wide asteroid. Almost all other dinosaurs, and most other life, would then die in the ensuing impact winter.
This, of course, is the asteroid impact that caused the extinction of all non-avian dinosaurs, as well as the loss of more than 70% of all species on earth.
Such a massive loss of life is known as a mass extinction. Throughout earth’s history, there has been five major mass extinctions, with the one that killed the dinosaurs being the most recent and well known. Known as the Cretaceous–Tertiary (K–T) extinction, while it is the most represented extinction event in popular culture (by far!), the K-T extinction was by no means the most severe. That title is held by the Permian–Triassic extinction event; also known as the Great Dying.
The extinction of almost all life
The great dying occurred 251 million years ago. Over the course of as little as 20,000 years, around 90% of all species went extinct, vanishing from the fossil record. Sea life was particularly affected, with 95% of all marine species being lost. Trilobites, who once dominated the entire ocean, were wiped out completely.
On land, things weren’t much better. Around 70% of all terrestrial vertebrate species went extinct, with large animals being more susceptible to extinction. Surviving the extinction were small, dog-sized, egg-laying, warm-blooded creatures called Cynodonts, who are the ancestors to all mammal species.
The effects of the mass extinction were so great that plants and insects, usually impervious to extinction events, also felt the pain. Approximately 50% of plant species, and 60% of insect species, did not make it.
After the extinction of most land animals, some species such as the Cynodonts were able to proliferate and diversify. Image courtesy of Nobu Tamura, via Wikimedia Commons
What caused this?
Unfortunately, as these events all transpired more than 250 million years ago, evidence regarding exact causes are scarce. Rocks that would tell us the exact cause of extinction have been either lost to the eons, or be buried under kilometres of rock. However, there are several credible theories on what happened.
The most commonly held belief is that the climate warmed due to extreme volcanism. The great dying coincides with the creation of the Siberian Traps, a huge volcanic field in Russia. The Siberian traps is an enormous plain of volcanic rock, created during 2 million years of continual volcanic eruptions that expelled an absolutely enormous amount lava and greenhouse gasses.
This volcanism would’ve produced short term effects such as blotting out the sun and creating vast amounts of acid rain. This alone had devastating effects on the environment, especially forests and marine life. However, the real killer was a huge increase in global temperature.
Estimates put the atmospheric CO2 at 2000ppm. In comparison, today the CO2 levels are at 410ppm. Global temperatures must have soared, warming equatorial waters to an average temp of over 40°C: 13 degrees higher than today’s average. Devastating to sea life, such an event would account for the extreme amount of marine species that went extinct.
There are other theories: a popular one suggests that there was an asteroid impact, similar to the one that killed the dinosaurs, that caused the Great Dying. Another states that the climate change was simply due to the formation of the supercontinent Pangea, and the subsequent changing of the ocean currents.
Ultimately, there is too little evidence for any theory to be the definitive truth. The cause of the greatest mass extinction of all time may forever remain a mystery.