First-year is full of professors quoting famous designers and philosophers, but one that really stuck with me was that “failures lead to successes and successes lead to failures.” He was referring to the Tacoma Narrows bridge collapse of 1940, in which advancements to modern bridge building failed spectacularly. Every process has its natural limit. Extinction events are the bridge collapses of evolution, and they typically happen once every 26-30 million years. These are truly catastrophic events that shape the face of the Earth for the next period of life. Extinction events occur gradually, happening when the overall rate of species extinction exceeds the rate of speciation. Fossil records are used to establish this, but these are not totally accurate. A large amount of the life on Earth is microbial in nature and does not leave traces behind in the fossil record. There are five major events that have been classified as the “Mass Extinctions”.
At the end of the Ordovician Era, 443 million years ago, most life was confined to the seas. The Ordovician-Silurian mass extinction took place when an ice age covered over the majority of the Southern Hemisphere. This dropped the sea levels and severely altered the chemical composition within them. After everything was said and done, around 85% of animal life had gone extinct. Around 80 million years later, the cycle was ready to repeat. The Devonian extinction was likely the effects of many events combined together. The seabeds in this era became devoid of oxygen, meaning that—except for bacteria—it was largely uninhabitable.
The worst extinction, known colloquially as “The Great Dying” occurred at the end of the Permian era. Sea creatures were the most badly affected group in this event, and insects, a group that is usually unscathed by extinctions, suffered badly as well. A multitude of catastrophic events, including sea level fluctuations, a drop in worldwide oxygen levels, as well as multiple meteor impact, led to around 96% of species becoming extinct. For anyone who’s counting, that means that all present day life evolved from the remaining 4% of species left. The Great Dying also marked the dawn of the dinosaurs and the Triassic Era.
The Triassic Era was bookended by another mass extinction, which lasted about 18 million years. Plants in this era were largely unaffected throughout the catastrophe, which is strange as they typically follow the trends of animals closely.
This brings us to the main event, the K/T extinction. By far the most famous extinction event, the Creataceous-Tertiary extinction—known as the K/T extinction—was also the most rapid of the mass extinctions. Rapid is a relative term though, and one heavily debated. Some theories require the extinction to take place in dozens of years, but the more widely accepted time frame is around ten thousand years. This is a far cry from what pop culture would have you believe. Many dramatisations of this event make it seem that a single event, the impact of the meteor known as the Chicxulub impactor, triggered an hours-long mass extinction. Palaeontologists now believe that the impact was the catalyst of an event that had been a long time coming.
Evidence of basalt eruptions around the world, intense climate change, and rapidly-dropping sea levels are all visible before the impact. Many special families had been on the road to extinction for many millions of years before the impact, and some actually continued to speciate for periods of time after it. Around three-quarters of life went extinct, including all non-avian dinosaurs. Various types of sea life was affected differently, with crocodiles surviving essentially unscathed and ammonites becoming completely extinct.
These are the five mass extinctions. There are of course many other smaller extinction events that have occurred in the lifetime of our big blue planet, but many of these are small-scale extinctions where the majority of life is unaffected. Extinction is a natural part of life, just like dying. We live in a period of climate change, mostly caused by our own species. This climate change is believed to have led to a large loss of global biodiversity, and many experts claim that even under conservative viewpoints we are in the midst of an extinction event. It is difficult for us to objectively view our own environment though, so skeptics claim that we can’t be sure of anything. Speciation in the wild is very difficult to track, and most species deemed extinct may yet survive in remote areas of the world. One example that hits close to home is the loss of honey bees in North America. Many would say that the bees are pests and unwanted, but bees contribute an enormous amount to pollination and the natural spreading of plant species. Newsweek estimates that with the lack of bees, the United States will produce $30 million less in produce this year.
This article may be an examination of extinctions, but extinctions also show how resilient life is. The measly 4% of all species that were left after the great dying evolved to survive and became the dinosaurs, who evolved and became today’s animal life. The world is going to keep spinning, and the cycle is going to keep turning over.
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