Life is good at dying, and there have been multiple periods in the timeline of Earth’s history where life was nearly obliterated for good. Extinction is a natural phenomenon in which all members of a species completely die off, and mass extinction events are some of the most dramatic happenings on Earth. Abrupt shifts in the environment can turn entire ecosystems on their heads, and whole families of animals can disappear in a geologic milli-second (which is why people should kind of, sort of care about critically endangered species).
Some threats came from outer space, like the violent meteor extinction of dinosaurs. Others, like the Holocene extinction, are caused by forces a little closer to home. Volcanoes, meteors, invasive species, climate change, and a host of other things can all trigger an extinction event, and there’s nothing to stop another one from happening. If we want to avoid a repeat of any of these calamitous events in our lifetimes, it may be wise to look at the history of mass extinctions and the devastation they bring with them.
The Great Permian Extinction Was The Most Severe In Earth's History
Also known as the Permian-Triassic Extinction, this event from 252 million years ago was so traumatic that it took about 10 million years for the planet to fully recover from it. 96% of all marine life and 70% of all land-based species vanished over the course of just a couple million years, an unprecedented rate of species loss. This mass extinction was so extreme that it is often referred to as “the great dying,” and it drastically reshaped all corners of life on Earth. In addition, this is the only mass extinction event known to have affected insects, some of the most resilient creatures on the planet.
There are many theories as to the cause of this great dying, including volcanic eruptions, increases in atmospheric methane, an asteroid, and even acid rain. Another suggestion is that the carnage was caused by Pangea, a super-continent that was the singular land mass at the time. Its shape may have stagnated ocean currents and caused a massive deoxidization of the sea. To this day, researchers worldwide continue to explore all the possibilities.
Also known as the K-T extinction, this is arguably the most famous mass extinction event of all. It put an abrupt end to the reign of the dinosaurs and was directly responsible for the rise of mammals. Dinosaurs weren’t the only victims of the disaster, as many as 70% of all species were killed off during this event. Non-avian dinosaurs, pterosaurs, ammonites, and the large marine reptiles that dominated the oceans were all obliterated. Even the animals that would go on to eventually survive and repopulate the planet didn’t escape unscathed, as species from all walks of life were affected.
The most popular and widely accepted theory as to what caused this terrible extinction is an asteroid impact powerful enough to significantly alter the Earth’s homeostasis. There is a lot of geological evidence to support this claim, including large deposits of iridium found in soil from the time. Iridium is rare on Earth, but it can be commonly found in asteroids.
The asteroid that hit the Earth is theorized to have been six miles wide and created a crater in the gulf of Mexico with a radius of over 100 miles. The impact would have filled the air with debris, causing a tremendous degradation of the atmosphere and killing off nearly every animal over 55 pounds.
Occurring around 2.5 billion years ago, this is widely believed to be the first-ever mass extinction event. The planet was very different at the time, as there was very little oxygen in the atmosphere. Life was relatively uncomplicated as well, having barely evolved beyond simple bacteria, most of which were anoxic. Anoxic bacteria don’t need oxygen to survive, and, in fact, oxygen is highly toxic to them.
This last bit would become a major issue for them upon the evolution of cyanobacteria, a new type of life that could harness the Sun's energy in a process known as photosynthesis. This brand-new adaptation for survival would have massive consequences, saturating the environment with a waste byproduct of the process: oxygen. Soon enough, the atmosphere began to fill up with oxygen, suffocating a majority of the anoxic bacteria on the planet.
Incidentally, the effects of oxygen in the atmosphere nearly wiped out the cyanobacteria themselves, as chemicals in the atmosphere reacted with oxygen to completely alter the composition of the air for good. This led to one of the worst global cooling events in Earth’s history, resulting in total oceanic freezes across the planet and the near death of all remaining life. Today, cyanobacteria is still abundant, and the remaining anoxic bacteria reside in oxygen-depleted biomes like the deep ocean.
According to a 2015 analysis of human hunting behaviors, researchers believe that humans should be considered “super-predators." Unlike other apex predators who hunt in ways that sustain an equilibrium between predator and prey populations, studies show that human predation habits may be inherently unsustainable.
Our ruthless efficiency when it comes to hunting is a unique trait in the animal kingdom. When animals hunt, they often target the youngest, most vulnerable prey. This minimizes potential risks of injury for the predators, and the most developed adult prey have the opportunity to repopulate. This is not true with humans, who are able to hunt adults of any species with relative ease due to the use of tools that minimize risk for human hunters. As a result, humans consume fish populations roughly 14 times as quickly as marine animals, and even apex predators like bears and lions are being hunted at 9 times the normal rate.
While the issue of human involvement in climate change and increased species extinction rates can cause division in the political world, there is a broad consensus in the scientific community that humans are largely responsible for these catastrophes. It is a well-documented fact that certain gases produced by human activity are the primary drivers of the current global warming trend, and this trend will have massive impacts on the environment.
As for extinction rates, experts say that the current rate is possibly between 10,000 and 100,000 times faster than normal. That means that we are possibly losing 2,000 unique species every year. Although the methods of confirming extinction rates are hotly debated, the fact remains that humans are having a massive effect on the environment.
The Triassic Extinction Happened In A Relative Blink Of An Eye
The Triassic period came to an end around 200 million years ago with this massive extinction, one that led to the end of half of all existing species. What’s remarkable about this event is the terrifying rate of death; nearly all of those species died off in less than 10,000 years. This extinction completely obliterated an ancient class of marine animals known as conodonts, as well as severely damaging the world's corals. Climate change, asteroid impact, and volcanic eruptions have all been cited as possible triggers for this event, but there has not been a scientific consensus on the exact cause.
With so many creatures wiped out so quickly, there was a lot of room for surviving species to branch out and diversify. This extinction event allowed for the rise of the dinosaurs, spectacular animals that would dominate the Earth’s surface for the next 180 million years.
The Ordovician–Silurian Extinction Events Ravaged Marine Life
Two different events that occurred back-to-back, the combined Ordovician-Silurian extinctions make up the second-most severe extinction event of all time and the first to significantly affect complex animal life. Marine species were hit particularly hard, with nearly 85% of all known species becoming extinct as a result.
Many theories exist as to what exactly caused this extinction, one of which is climate change. A cooling event may have led to increased glacier formation that lowered sea levels and destroyed many marine habitats. Another suggestion has been large-scale metal poisoning of the oceans, which caused atmospheric oxygen depletions. A rogue gamma ray burst may also have been responsible. It’s hard to know for sure, as this event took place over 400 million years ago. New theories are still being proposed, so perhaps one day we will know the cause of these massively destructive events.
