One of the realities of living on planet earth is that every species that exists or ever has existed did so while in the precarious position of always being in danger of extinction. While asteroids tend to come to mind when talking about extinction events, many other things can, and have, caused them. Hi! I’m Johhny and today I’m counting on 10 Major Extinctions Of Planet Earth.
10. The Ordovician Extinction
Number tenth on my list is the second worst known to have happened on planet earth killing an estimated 86 percent of all species of marine life. Occurring between 455 to 430 million years ago, this extinction is most widely attributed to climate change and a drop in sea levels, however, there is also a hypothesis that the disappearance was initially kicked off by a gamma-ray burst. If this was the case, the likely source was a hypernova that may have occurred about 6,000 light years away. Gamma-ray bursts of this type are short, but the levels of radiation would have been such that in only a few moments earth’s ozone layer would have been severely depleted by as much as half. This would have exposed anything near the surface to ultraviolet light from the sun, and thus mass death.
While it’s not likely we’ll ever know if this extinction was in fact due to a gamma-ray burst, it does highlight that such explosions do pose a threat to life on earth, and should one ever occur nearby it would have devastating consequences on our world and threaten us with extinction. Worse, there is nothing we currently could do to stop it, though in the far future orbital planetary shielding might be an option.
9. The Pliocene-Pleistocene Extinction
This relatively minor extinction event isn’t well documented, but it seems to have affected mainly marine life, but it’s noteworthy because it may also have been induced by an astronomical phenomenon, though very different from a gamma-ray burst. There are two possibilities here. The first is an asteroid impact that is believed to have occurred in the south Pacific about 2 million years ago. The evidence comes in ocean sediments that were disturbed but also had layers which were shown to be high in the element iridium, which is rare on earth, but not so in asteroids. This event, known as the Eltanin impact, is thought to have been caused by an object several kilometers wide, creating a crater tens of kilometers in diameter. But there is also other physical evidence of the aftermath in the form of geological features found in the Pacific ocean. When the Eltanin asteroid hit, it produced a tsunami estimated to possibly have been over 600 feet high when it hit land and might also have affected life by jump-starting an ice age, though some researchers counter that this event had no effect on life on earth at all.
The other possibility is that a supernova might have damaged the ozone layer and caused a mass die-off of marine life. This possible supernova is linked to the relatively close passage of the Scorpius-Centaurus star cluster to earth. This would also explain the presence of certain astronomical features local to our part of the galaxy, and even the presence of certain iron isotopes in the earth’s crust.
8. The Volcanic Extinctions and Clathrates
This entry is more of a class of extinction causes that might have been responsible for many of these events in earth’s history. These are geologic extinctions and can occur from periods of intense volcanism where an increase in volcanic gases changes the composition of the atmosphere, but also resultant fires that come together to create changes in climate. Should a supervolcanic eruption happen today, such as the potential eruption of Yellowstone, this is a leading global risk for our possible extinction, though the good news there is that we’ve survived these kinds of explosions before.
Volcanism can be studied and even predicted these days so we would likely have warning ahead of time. Not so much the case for another type of possible geologic mechanism for extinction though. It could come without warning, unfold very rapidly and once it ’s triggered, it’s irreversible like a flying bullet. Its known as a clathrate gun, and may have contributed to several extinction events in the past. Methane in earth’s seabeds occurs in a form called a clathrate, basically a mix of water ice and methane. During periods of oceanic warming or drops in ocean levels, the clathrates can release methane rapidly, which is a potent greenhouse gas. This, in turn, creates changes in climate which contribute to extinctions, but can also cause inevitable changes in ocean acidity.
This may have been a contributing factor in earth’s worst extinction event, the Permian-Triassic, which occurred about 252 million years ago. This event seems to have pulsed in three different waves of death, meaning that there may have been several causes, including a clathrate gun, volcanism, and also a possible asteroid impact. The estimated numbers for this extinction event, also known as the great dying, are astonishing. Seventy percent of vertebrates went extinct, and a whopping 96 percent of marine species, and the one group of life on earth that commonly weathers extinction events quite resiliently, the insects, also experienced mass extinction during this period.
7. The Carboniferous Rainforest Collapse
Though a relatively small event in comparison to the others on this list, this was a particularly weird extinction in that the initial victims themselves, in this case, plants, were ultimately the cause through fatal growth patterns perhaps brought on by climate variations or other reasons. It happened about 305 million years ago. This was a period of rainforest environments on Earth’s landmasses where the plants were developing rapidly and changing their habitat along the way. This seems to have led to the rainforests breaking up into increasingly isolated islands until they could just no longer sustain. This, in turn, caused the extinction of animal life and a drop in planetary oxygen levels.
6. The Cambrian Extinctions
This was a period of three successive extinctions starting about 517 million years ago and culminating at the end of the Cambrian period approximately 488 million years ago. The first event was a mass die-off of small shelled ocean animals, and then a second event evidenced by trilobites for a combined die-off of about 40 percent of marine species on earth. This then gave way to the Cambrian-Ordovician extinction, which killed off a vast number of trilobite species and also many of the brachiopods. One hypothesis for the cause of this event is that oxygen in the oceans somehow became depleted and many species couldn’t cope.
5. Olson’s Extinction
This extinction is particularly spooky because even though it was widespread and affected many different species across the board, it’s a huge mystery as to just what caused it. Whatever it happened about 273 million years ago, and even though this event has been known for decades, no widely accepted explanation for it has surfaced. However, one idea is that a sudden change in climate occurred, but what caused that is unknown. It’s thought that it took a very long time for the earth to recover from this particular event, and may have made the effects of another mass extinction, the Permian-Triassic extinction event worse, leading to a total combined body count of 80 percent of all species living on earth at the time.
4. The Holocene Extinction
Not all mass extinctions are lost in the mists of time, and in fact, there’s one going on right now. And we are the cause. Termed the Holocene extinction, it’s due partly to overhunting, we may have played a significant role extinction of megafauna in pre-history, but the vast majority of extinctions that have gone on during the age of humanity have gone undocumented and are merely due to the competition we create due to our activities. This can be the destruction of habitat, pollution, and even introducing non-native species to areas where they can outcompete the native species and drive them to extinction. But this is a strange type of destruction in that the very civilization that caused the disappearance of a species has, over recent decades, moved towards gaining the ability to reverse extinction through the study of genetics and might eventually bring back fauna that was formerly extinct.
While this doesn’t help long-extinct species that we have no DNA surviving from, it does open the possibility, along with management of endangered species, of mitigating the Holocene extinction.
3. The Toba Supervolcano
This event was more of an almost extinction, rather than proper destruction. But I include it on this list because one species that it may have nearly driven into oblivion was us. The eruption of the Toba supervolcano is thought to have occurred about 75,000 years ago and represents the biggest class of supervolcano eruptions possible on this planet. Just how disruptive this eruption was is not yet well understood, in fact, recent studies suggest that it might have released more ash into the atmosphere than previously thought. But there is evidence that it may have caused a cooling effect in the earth’s atmosphere that took as much as a thousand years to recover from completely.
However immediately following the eruption, the effect could have been much worse depending on how much the temperatures dropped, and how long the effect lasted, though this is all debated. In short, the severity and impact of this event are not yet well understood. However, genetic evidence suggests that modern humans descend from a relatively small gene pool, suggesting that our population might have bottlenecked at some point, presumably due to some disaster. It’s estimated that if this bottleneck did indeed occur, it happened roughly about 70,000 years ago, close to the timeframe of the Toba eruption and its after-effects. However, we seem not to have been the only species to bottleneck during that period. Several other primate species, and also cheetahs and tigers, appear to have been reduced in population size severely at roughly about the same time. Even at this time, DNA evidence seems to indicate that a significant migration of humans from Africa occurred. If Toba wasn’t responsible for all of this, one wonders what was.
2. The Cretaceous-Tertiary Impact
Out of all of the extinction events, planet earth has witnessed, this one is the most widely known. In this single event that occurred about 66 million years ago, three-quarters of all animal and plant life in this world went extinct. Most famously went the dinosaurs other than the ancestors of the birds, but almost everything weighing more than 25 kilograms died out.
This extinction, of course, is believed to have been due to an asteroid collision, which is thought to have hit roughly in the area of today’s Yucatan peninsula, but there may have been more factors than the impact, including volcanism and climate disruption. But the effect itself would have been a real vision of chaos and hell. Studies done in 2016 showed that the asteroid almost instantly carved out the seafloor and then into the granite below ejecting enormous amounts of material into the air.
Additionally, they found evidence of what must have been a truly massive amount of sea water moving. What the study didn’t notice, however, was the mineral gypsum. Gypsum comprised much of the seafloor bedrock in this area, meaning that the impact literally vaporized the seafloor upon hitting it, sending the rock vapor into the atmosphere disrupting earth’s climate and food chains. The only good to come out of that event was that it created an opportunity for anything that survived to evolve if it could find an advantage. That state of affairs would ultimately lead to us. One wonders what might have been had this extinction event never happened.
1. The Great Oxygenation Event
This event is unique in that not only was it an enormous mass extinction, but the actual cause of that extinction is vital to complicated life on earth. It’s oxygen, and while that eminently natural gas sustains our hungry brains today, to certain other types of life, it is deadly poisonous and once caused the extinction of much of the anaerobic life on planet earth. And, if that wasn’t enough, it may have also sparked periods of massive glaciation and even more extinctions.
The oxygenation event is thought to have occurred about 2.45 billion years ago. Sometime before that, the cyanobacteria began to photosynthesize and release free oxygen into the atmosphere. For a time, this was mitigated as surface iron and other factors trapped the oxygen again through oxidation, in other words, the metal rusted, but once that process ground to a halt and the oxygen could then build up, it began to poison the anaerobic organisms living on this planet that couldn’t handle the presence of it.
But there was another aspect to this that probably made things much worse. Oxygen also started to affect earth’s methane and carbon dioxide levels, both greenhouse gases. That far back in time, the sun did not radiate as brightly as it does today, meaning that as greenhouse gases disappeared earth cooled and went into what is known as the Huronian glaciation. This period was so bad that some researchers think that earth almost entirely froze over. What may have followed was a nightmarish cycle of atmospheric gases changing in tandem with drops and rises in photosynthesis leading to warmer interglacial periods, and then back to cold conditions. What eventually broke this cycle is uncertain, though one wonders if there are Earth-like planets in the universe that never do break that kind of a sequence, and life on those worlds forever remains microbial. Perhaps earth got lucky in this regard.
But it likely won’t stay lucky forever. Our planet has seen many mass extinctions in its past, and this list covered only a sampling of them, and it eventually it could see natural mass extinctions again. As our technology advances though, we are steadily gaining the ability to avoid mass extinctions through space technologies to deflect asteroids from collision courses and other methods. Given enough time and development, even supervolcanic eruptions might become avoidable. And yet the final complete extinction of life on earth that will occur as our sun ages might be preventable by migrating planet earth further from the sun. So maybe there will come a day where mass extinctions no longer occur on planet earth at all.
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