The end is nigh – but how nigh we have absolutely no idea. If there is one subject that humans have consistently struggled to come to terms with, it is the concept of an extinction event. An act so all-encompassing, so catastrophic that it signals the end of life as we know it.
Today we frequently discuss the effects of climate change on the planet, along with the humans and animals that inhabit it, but it is important to remember that we are simply living in a single stage of history that goes back around four and half billion years. Humans have unquestionably exacerbated the problem of climate change, but our climate has changed dramatically countless times since the creation of the earth, with enormous consequences.
Waters rise and fall, ice comes and goes, temperature soar and plummet – that seems to be how it’s always been on this rock hurtling through space that we call home. In the past, this led to devastation that wiped out almost all living beings, but climate change is just one of the many ways the world could end.
Whether it’s a giant comet or meteor slamming into the Earth, a super-volcano unleashing absolute hell, or even a virus that kills all before it, we are constantly treading a fine line. We continue to bicker among ourselves, fight wars, and generally believe that we’re indestructible – but that’s far from the case. Extinction events are terrifyingly real – they’ve happened numerous times before, and they will happen again.
Before we dive back hundreds of millions of years to examine the first known extinction events let’s begin with some facts. Extinction events, also known as mass extinctions or biotic crises, are classified as a widespread and rapid decrease in the biodiversity on Earth, in which the
rate of extinction far outstrips the rate of speciation – natural evolution.
Extinction has been part of life for as long as life has existed. It’s thought that around 99.999% of all life that has ever lived is now extinct, either through natural selection, genetic problems or these large-scale events that have almost completely wiped out a planet’s many specifies.
As we’ll get to shortly, these events can be down to several factors and sometimes numerous factors occurring at the same time or overlapping. They can be caused by natural climate change, altered weather patterns, meteors, volcanoes, earthquakes, and much more.
The term ‘extinction event’ can be a tricky one to discuss because there are no clearly defined parameters around it. Some of the events that we’ll look at destroyed as much as 95% of the species on Earth, while others were more like 70% – which seems to be the lowest benchmark for an extinction event. It seems logical that there has never been an event that killed off absolutely everything out, for the obvious reason we are here and we must have evolved from something.
One of the stranger facts about extinction events is that they appear to come in a rough pattern. It’s thought that these events occur roughly every 26 million to 30 million years, but we have little to no idea why.
There have been some wonderfully outlandish theories, including the presence of a twin star to our own sun lying somewhere outside the Ort Cloud which may have affected the Earth’s natural cycle. In 1984, this hypothetical star was labelled rather aggressively as ‘Nemesis’, but scientists have continuously failed to locate its presence.
Other theories for the supposed extinction pattern include the close passage of other stars or the angular effect of the galactic gravity plane working against the outer solar orbital plane, but in reality, we’re still nowhere near understanding why this occurs.
We know that the Earth is roughly 4.5 billion years old and according to most there have been five major extinction events and numerous minor. However, this doesn’t quite tell the whole story as the five major events all lie within the Phanerozoic Eon, the current geologic eon that stretches back around 541 million years and includes the period when the most abundant animal and plant life has existed.
Moving further back from the Phanerozoic Eon makes it much harder to gauge the number of species and level of habit on the planet, and what, if any effect global events could have had on them. But this is exactly where we are going to begin, with an event that occurred between 2 and 2.4 billion years ago.
The Great Oxidation Event
Walk outside and take a deep breath and you will fill your lungs with a gas that is indispensable to not only humans, but life across the planet. Without oxygen, human life would end in a matter of minutes, and while other animals might be able to go a bit longer, it would be catastrophic for most species on Earth.
Over 2 billion years ago, however, things were very different. At that time, the Earth’s water and its atmosphere held precious little oxygen, certainly far less than would be needed for large animals. But the Great Oxidation Event completely flipped this situation when for some unknown reason, biologically-produced molecular oxygen started to accumulate in Earth’s atmosphere, transforming it from unlivable for large specifies with almost no oxygen, to our current abundance capable of sustaining life across the planet.
But while this was good news for us and other larger species, the Great Oxidation Event effectively wiped out many existing anaerobic species – organisms that don’t require oxygen. As we’ll see as we move on, an extinction event, though it may be terrible, often leads to the rise of other forms of species further on down the road.
The Late Ordovician Mass Extinction
The first of the five major extinctions that occurred during the current Phanerozoic Eon, and still believed to be the second-largest of all time, was the Late Ordovician Mass Extinction, which mainly occurred across two waves between 440 and 450 million years ago, at a time when most species on Earth lived in the water.
This event eliminated 40–60% of marine genera (living and fossil organisms) and nearly 85% of marine species, causing the extinction of one-third of all brachiopod and bryozoan families, as well as numerous groups of conodonts, trilobites, echinoderms, corals, bivalves, and graptolites.
What’s interesting about this event is that it occurred just after – and when I say just after I mean 50 million years or so – the Great Ordovician Biodiversification Event which was one of the largest and most intensive evolutionary radiation of species ever seen on Earth. This was a time when biodiversity and fauna boomed, though strangely it didn’t occur at the same time around the world. Patches of the earth seemed to move faster than others, but over tens of millions of years, it left the Earth completely transformed.
That was until the Late Ordovician Mass Extinction, which pummelled the newly thriving planet. It seems it began at least with glacification, particularly in the Himalays, but may also have been linked with an increase of anoxic water – water that is depleted of dissolved oxygen – or perhaps even a toxic metal that may have dissolved in seawater.
Permian–Triassic extinction event
To give you a good idea of just how catastrophic the Permian–Triassic extinction event was, it has long come with the apocalyptical sounding nickname ‘the Great Dying’.
Yet while the name might sound a little over the top, it really is quite appropriate. Roughly 90% of the species on Earth were wiped out by this event, which occurred around 253 million years. This included 57% of biological families, 83% of genera, 81% of marine species and 70% of terrestrial vertebrate species.
Such was the destruction that living, breathing organisms didn’t fully return to the planet for another 10 million years. You probably won’t then be surprised to hear that the Great Dying was unquestionably the worst extinction event ever to hit the planet.
Again, pinpointing exact causes is difficult, but there are some strong theories here. Roughly 250 million years ago one of the largest volcanic events in history occurred which completely transformed northern Russia, and created was is known today as the Siberia Traps, a large area of basaltic lava that covers 7 million km2 (3 million sq mi).
This eruption was monstrous and is thought to have continued for a staggering two million years – just try to get your head around that one – while completely decimating the climate and life on Earth. It’s thought that around 20% of the output of the Siberian Traps eruption was pyroclastic (ash and other debris) which was pumped straight up into the atmosphere, dramatically lowering global temperatures.
But what’s more, it may not have been the only planet-altering volcano to have gone off around that time. The Emeishan Traps eruption in south-western China, which occurred around 260 million ago, may have been a smaller event than in Siberia, but it quite possibly contributed to the chaos seen around the world.
These two events, along with several other factors, such as a potential rise in methane in the atmosphere, widespread anoxia, and if that wasn’t all bad enough, perhaps even a meteor strike, caused the most serious extinction this planet has ever faced.
The Cretaceous–Paleogene (K–Pg) extinction event
The Cretaceous–Paleogene extinction event, also known as K–Pg, is certainly the most famous and occurred 66 million years ago, at a time when the dinosaurs roamed freely as they had for around 180 million years before that. This all changed in spectacular circumstances when a meteor, 13 kilometres wide (8 miles), breached the Earth’s atmosphere and slammed into land in the Yucatán in modern Mexico at around 72,000 km/h (45,000 mph).
The immediate effects were dramatic as it opened up a crater 180 km (110 miles) wide and 19 km (12 miles) deep, now known as the Chicxulub crater. Anything within 1,450 km (900 miles) would have been destroyed almost instantly, but it was the months of darkened skies and debris spiralling up into the atmosphere that put an end to the dinosaurs, along with 75% of all species on the planet.
Not only did practically all plant life die quickly, but global temperatures plummeted as a result, killing off most species that would become extinct within just five months. Omnivores, insectivores, and carrion-eaters survived the extinction event, but no herbivorous or carnivorous mammals prevailed. Small mammals and birds were able to survive, often feeding on insects, worms, and snails, which themselves fed on dead plants and decaying animal matter – something there was suddenly quite a lot of.
But again, this was one extinction event that actually led to the widening of species. With dinosaurs dominating the planet there was precious little room for large mammals and certainly not for us weakly Homo Sapiens. By removing the great beasts from the ecosystem, it at least allowed for the possibility for humans to thrive – around 65.5 million years later.
The Ongoing Holocene extinction
Some argue that we are amid the sixth great extinction event, often referred to as the Holocene Extinction – mainly caused by human activity. We are absolutely trashing the planet and it’s thought that the current rate of extinction of species is estimated to be 100 to 1,000 times higher than natural background extinction rates. This is often linked with overhunting, an overreliance on meat, increased levels of CO2, overfishing, and widespread loss of biodiversity to name just a few.
While other species are becoming extinct at a terrifying rate, Homo Sapiens are doing rather well, with the global population expected to rise past 9.7 billion people by 2050. But what this means for humans is certainly not clear. Some suggest that this figure could prove to be a high point followed by either a gradual or sudden drop in numbers as we move towards the end of the century. Whether this will be down to concerted efforts at population control or more extreme circumstances such as food insecurity, war or viruses, we’ll just have to wait and see.
And this brings us nicely up to date and where we can start looking to the future. Whether you want to consider the current period an extinction event or not, it’s impossible to escape the fact that another major event is almost certainly going to happen in the future, whether that be tomorrow or in a million years.
Doomsday scenarios are a topic that we both love and find deeply uncomfortable. They enthral us when presented within the safe confines of fiction, but the mere possibility must surely be one of the most terrifying prospects imaginable. What’s been clear during the Earth’s lifetime is that it has experienced a regular-ish pattern of extinction events, whether down to asteroid strikes, volcanoes, natural climate change or other factors.
Significant strides have been taken in recent years to address the possibility that we might be on the receiving end of another massive meteor or comet at some point. Films like Armageddon and Deep Impact brought the possibility into the mainstream public consciousness and there have been several space missions recently that have looked at possible methods of deflecting an incoming space rock away from the Earth.
So just how common are meteor or asteroid strikes? Well, the good news is not very common at all, but the news is it’s been quite a while since the last major impact. On average, an asteroid or comet with a diameter of 1 km (0.62 mi) hits the Earth every 500,000 years, while what is considered a large collision, with a diameter of 5 km (3 mi) or more, happens about once every 20 million years.
NASA says the probability of a city being destroyed by an asteroid is 0.1% each year, and even if one does come through our atmosphere, there is a 70% chance it falls in the ocean and a 25% it will hit in a remote area with little to no major damage.
If we’re talking about an asteroid or comet similar to what wiped out the dinosaurs, it’s thought odds are a minute 0.000001%, though some argue that because something like this happens every 50-70 million years, and since the asteroid that led to the KpG extinction event occurred 66 million years ago, you might say we’re due one – give or take a few million years.
Volcanoes litter our planet and continue to remind us of their immensity and brutal force. It’s thought that there are between 10 and 20 ‘supervolcanoes’ around the world and if one of these beasts ever went off it could well trigger an extinction event. Luckily, these types of eruptions occur relatively infrequently, every 100,000 years or so, with the last major supervolcano eruption, the Oruanui eruption of New Zealand’s Taupō Volcano coming around 26,500 years ago.
When we normally think about volcanic eruptions we generally think about a few big booms with plenty of lava, but an event that quickly quietens down. A supervolcano eruption can in theory span a massive amount of time, potentially a couple of million years, in which the global climate would be completely changed and life as we know it utterly destroyed.
Yet while volcanoes and comets might provide the best Hollywood scripted end to the world, it could come in a wide variety of ways. It’s not inconceivable for a virus to wipe out large swaths of the planet, or a gradual change in our atmosphere that means that living on Earth became impossible for most animals and humans. And speaking of Homo Sapiens, since the advent of nuclear weapons we have retained the power to cause our own extinction event and there were certainly a few instances during the 20th Century where the world seemed to wobble on the brink.
When we talk about these kinds of events we often use the term end of the world, but as we’ve seen that’s not quite right. Our world has proven time and time again that it can bounce back from cataclysmic disasters, often over several million years. However, the fate of the species that reside on this floating rock is quite a different story. We like to think of ourselves as superior and in many ways bulletproof, but if history has taught us anything it’s that when it comes to extinction events, even the mighty fall – and fall hard.