The last great extinction event saw an asteroid larger than Seattle strike Mexico and eradicated the dinosaurs, with the rise of mammals (and more recently, humans) coming soon after
To check out Part One of The Human Story, click here.
When you ask someone when the last time a massive apocalyptic event occurred on earth, the answer is almost always related to the Cretaceous–Paleogene (or K-Pg) extinction event which occurred some 66 million years ago, more commonly known as the extinction of the dinosaurs.
Today, children are taught about the estimated 10 kilometer (6.2 mile)-wide asteroid that impacted what is now the Yucatan Peninsula in Mexico, the result of which was an apocalypse of biblical proportions that wiped out the majority of all life on Earth.
What people often forget however is that the extinction of the dinosaurs, up until the 1980's, was thought to be the result of gradualism by most in the scientific community.
If one were to study paleontology and ask questions about exactly why so many species were wiped out in a relatively small time period, the answer that was instilled in students and academics across the world largely boiled down to simple Darwinism - that natural environmental and resource changes other animals were more suited to exploit caused the gradual decline and extinction of the dinosaurs and many other species of animal.
It wasn't until the late seventies when an American geologist named Walter Alvarez and his Nobel-prize winning physicist father Luis proposed that the extinction period during which the dinosaurs were wiped out was not the result of a gradual shift, but a catastrophic event that was caused by a massive impact and the fallout it left in its wake.
Published in 1980, he theory was largely based on the presence of a dark layer of clay (often referred to as a "black mat" layer) found by geologists in many areas that marks the Cretaceous-Paleogene (or K-Pg) boundary, which at that point had not been explained; the Alvarez's however found that upon studying one such K-Pg boundary in Italy, the geological layer was abnormally rich with iridium.
Although iridium is rare on Earth, it is not unusual to find trace amounts of it; the amounts found in the K-Pg layer however were as high as 160-times the amount found in other layers.
The Alvarez's hypothesized this abnormal concentration of iridium was spread into the atmosphere when an asteroid (which often feature iridium in abundance) impacted the Earth and was subsequently vaporized, with the iridium eventually settling on the surface along with other material the impact produced to create the iridium-enriched clay.
The theory was of course widely rejected by paleontologists and the broader scientific community, but subsequent reports finding similarly high iridium concentrations in the K-Pg boundary in other areas all around the globe had many scientists struggling to explain how else the rare element could have otherwise gotten there.
Walter Alvarez and his father, along with many other scientists determined to get to the bottom of the mystery, did their best to find an impact crater that could serve as the definitive proof of this theory. Unbeknownst to them, their theory's smoking gun had already been discovered (or perhaps more accurately, re-discovered) by a pair of geophysicists working in Mexico.
In 1978, Glen Penfield and Antonio Camargo were working as part of a team conducting an airborne magnetic survey of the Gulf of Mexico for the Mexican state-owned oil company Petroleos Mexicanos (better known as Pemex).
Penfield and Camargo were tasked with scouting possible locations for oil drilling using the geophysical data the survey returned, but while reviewing the offshore magnetic data collected, Penfield noticed an anomaly.
After comparing the anomaly he found with previously generated onshore gravity data he obtained from the 1940's, Penfield mapped a shallow "bullseye" roughly 180 kilometers in diameter centered just off the northern coastline of the Yucatan Peninsula. Penfield believed this feature, which appeared amongst otherwise uniform and non-magnetic surroundings, was clearly an impact site.
Similarly, about a decade prior to this discovery, another contractor for Pemex by the name of Robert Baltosser had also found that same crater, but corporate policy prevented him from publicizing his findings.
Like they had done with Baltosser, Pemex rejected Penfield's crater theory as they believed the feature was formed by volcanic activity. Undeterred, Penfield and Camargo convinced Pemex to let them present their findings (absent some of the data Pemex wished not to fall into the hands of competitors) at a geophysicist conference held in 1981.
Their presentation, although intriguing, didn't spark much interest in the field as a whole, though smaller publications such as The Houston Chronicle featured Penfield and Camargo's findings thanks to an interested journalist by the name of Carlos Byars.
Penfield would continue to try and collect conclusive physical evidence of the impact crater on his own; after seeing the impact theory paper Walter Alvarez and co. had published in 1980 in Science, Penfield even wrote to Alvarez to share his findings. Unfortunately, he would receive no response and eventually abandoned his efforts after being told earlier Pemex exploratory drilling site samples (which could have proven the site was indeed an impact site) were either lost or destroyed and his attempts to return to the drill sites failed.
It wasn't until 1990 that Penfield's discovery would gain the attention of others in the scientific community and lead to a revelation in the scientific world.
The Houston Chronicles journalist Carlos Byars, while speaking to University of Arizona grad student Alan Hildebrant, shared his recollection of Penfield's potential discovery that he had been so intrigued by nearly a decade prior. Hildebrant, who had been searching for a crater near the Brazos River in Texas, was thrilled at the prospects of such a site and reached out to Penfield directly.
The two men were able to secure a pair of drill samples from the Pemex wells Penfield had previously tried to obtain years prior, which had actually been safely stored in New Orleans the whole time.
Upon examination, the drill samples clearly showed shock-metamorphic materials, proving the site was indeed caused by an impact.
A team of California researchers surveying satellite images in the area also found a cenote ring centered on the town of Chicxulub Puerto in Mexico; Hildebrand, Penfield, Camargo, and several others published their findings in a paper in 1991 which named the impact site the Chicxulub Crater after the small town near the crater's center. Penfield later claimed that part of the motivation for naming it after the town was that naysayers in academia and at NASA would have a hard time pronouncing it.
After over a decade of mounting evidence, the Alvarez's impact theory finally had the definitive proof it had been searching for, as multiple subsequent studies dated the crater to a little over 66 million years ago, placing it exactly when the the K-Pg extinction was estimated to have began.
Since then, it has been widely accepted and disseminated by academia and the mainstream media that it was a massive asteroid impact and the ensuing chaos it caused that wiped out the dinosaurs and most of all life on our planet some 66 million years ago.
The historic impact is estimated to have generated a blast equivalent to some 100 million megatons (or 100 teratonnes) of TNT. To put that into perspective, the most powerful atomic bomb ever detonated, the Tsar Bomba, had a force of approximately 50 megatons, meaning the Chicxulub asteroid impact was equal to up to two million of the most powerful atomic bombs humans have ever detonated.
The Little Boy, the atomic bomb that destroyed Hiroshima in 1945, had a blast yield of just 15 kilotons - meaning the asteroid impact had a yield nearing 6.67 billion times greater than an atomic bomb that immediately killed approximately 80,000 people right after detonation.
Although an appocalyptic event served as the catalyst for the mass extinction of dinosaurs and so much of Earth's flora and fauna at the time, the gradualists weren't entirely wrong, they were simply missing (or more accurately, dismissing) a crucial piece of the puzzle.
The impact and short-term aftermath of a meteor with a diameter the height of Mount Everest hitting modern-day Mexico wiped out the majority of life on our planet, but that alone didn't wipe out all of the dinosaurs; instead, the dramatically altered environmental conditions post-impact saw other species of animals that were better adapted to survive those new conditions rise to prominence while the remaining dinosaurs (and many other species of their time) dwindled in number until they joined the ranks of the extinct.
You may be wondering however, what does the extinction of the dinosaurs some 66 million years ago have to do with humans and our own ancient history?
The story of the last widely accepted major extinction event Earth has gone through is an important part of the human story for several reasons.
For starters, mammals, which largely existed in small forms such as monotremes (animals like the platypus and echidna for example) and served as food for the dominant dinosaurs, would come to dominate the planet themselves in the wake of their fallen friends.
Primates would pop up in the fossil record at least 55 million years ago, eventually leading to the advent of hominids some 6-7 million years ago, then came the first species in the Homo genus (Homo habilis) nearly 3 million years ago, and eventually Homo sapiens walked the Earth at least 315,000 years ago.
Just as importantly, the story of the dinosaur extinction highlights the scientific process and the flaws in our education system.
Science is never "settled" - virtually everything in science is simply a theory that needs to be re-evaluated anytime new evidence or possibilities emerge. Even gravity is a theory; it is often misconstrued as a fact because we can see and feel its effects, yet exactly how it works and why is still a work in progress.
This is of course the great thing about the scientific process, in that even longstanding "rules" are challenged and can be rewritten should sufficient evidence be discovered.
It is however also a problem when our education relies so heavily on preaching scientific theory and often presents these theories as fact - like in the case of gradualism being taught before the impact theory provided concrete evidence to prove simple natural changes over time weren't a sufficient explanation.
Concepts like gradualism are often embedded into academia because they are "safe" and logical - they make sense and don't involve anything too exciting, and often have elements that there is evidence for, so they must be true until something with undeniable evidence comes along.
The problem is, rarely does our education system emphasize the theory aspect of their teachings, and thus after learning about certain theories or "facts" as they're often presented in school tests and textbooks, people begin to believe what they are told is immutable fact and that other explanations aren't a possibility.
Those beliefs are regularly reinforced through media, whether it be through news, documentaries, movies, TV shows, books, or even social media. It then takes a tremendous amount of time, effort, and evidence to change any longstanding theories or "facts" which have spread through society, even if the initial theory or "fact" was based on incredibly flimsy or non-existent evidence (we'll get into much more of that later in this series).
It was taught, it was repeated, it was reinforced, and therefore it is true.
The demise of the dinosaurs also serves to highlight a constant danger that has threatened our planet's existence and the life it fosters since that life first began on Earth: extraterrestrial visitors.
Death From Above
As any animal inherently knows, life in the wild is dangerous, and the Earth as a whole is no exception.
There are many threats to the existence of the blue planet we call our home, from a massive solar flare wreaking havoc to a black hole swallowing up our entire solar system, but the most consistently troubling danger has always come from unwelcome visitors from elsewhere in (and sometimes, entirely outside of) our solar system.
No, I'm not talking about aliens. The real threat, and one which has scarred our planet time and time again, is from asteroids.
Most people haven't heard of many (if any) other major asteroid impacts besides the one that left the Chicxulub crater, but there have been many massive impact sites found to date, including one in South Africa that is considerably larger than the one that took out the dinosaurs and is believed to have caused a similar extinction event some 2+ billion years ago.
You can easily find a list of massive impact craters on Wikipedia which shows all of the confirmed sites known of to date; the problem is, just like the vast majority of finds relating to ancient history on our planet, the discovery of such evidence is often made by accident, typically uncovered during construction projects or in the planning phases of said projects.
There are many other problems with getting a truly comprehensive picture of just how many massive impacts our planet has sustained, even in more "recent" history - while we know that such impacts have occurred quite often when viewed on a cosmic scale, we call our home the "blue planet" for a reason - most of our world is covered in water. Should a meteor impact occur in an ocean, the chances of us finding proof of this becomes extremely low, yet such an impact would still have massive ramifications for a continent or even the entire world.
In the past, much of the Earth was also covered in massive glaciers, which if impacted would not leave the same kind of evidence behind as a land impact (or an impact in shallow waters).
One need only think of Antarctica to understand this - the icy continent boasts 9% of the Earth's land mass, yet of 190 confirmed impact craters found in the world, not one has been found there.
This is of course understandable given that its surface is covered in snow and ice and has not seen much human study at all compared to any other region, but it's virtually impossible that the continent hasn't been hit by large asteroids at some point just like every other land mass on Earth.
In fact, over 60% of all meteorites that have been found and cataloged have come from Antarctica, as the small rocks are easily preserved in the desert conditions and easy to find given their contrast with the snow and ice; impact craters from larger meteors are of course much harder to spot under such conditions.
You may be thinking, if an asteroid lands in the middle of the ocean or hits a glacier, surely that wouldn't cause as much damage as if it hits land?
Well, not exactly.
A sufficiently large asteroid that manages to enter Earth's atmosphere is effectively a massive, rocky fireball travelling at tens of thousands of miles an hour toward whatever is unfortunate enough to be in its way.
Our planet does have a built-in defense for the many asteroids that venture into its neck of the woods - its atmosphere.
For a quick idea of what the Earth would look like without its atmosphere, simply look at the moon - a giant rock completely covered in craters.
You can even see the atmosphere's defensive ability in action anytime there's a meteor shower.
A meteor shower occurs when comets (instead of flying space rocks, comets are balls of ice and dust) enter Earth's atmosphere, where the friction encountered when it runs into our planet's protective layer causes the flying ball of debris to burn up before either skimming past our planet (if it's large enough and depending on the trajectory) or it vapourizes entirely.
A similar thing happens with small asteroids that enter into Earth's atmosphere (once an asteroid enters atmosphere, they're then called meteors) - the friction created by the gases in our atmosphere burns up the projectile, effectively becoming nature's firewall.
Now one of a few things can happen with that meteor however - one, it can burn up entirely or to the point of being miniscule, the heat from the friction between the incredibly fast-moving projectile and the increasingly thick atmosphere disintegrating it on it's way toward the planet's surface; or two, it can break apart into smaller pieces that either burn up or similarly land on earth with a mere fraction of its original force and size.
When one of those pieces does manage to make it to earth's surface, it's called a meteorite.
Occasionally, an asteroid is big enough to make it through our atmosphere intact without burning up into a tiny, virtually inconsequential fragment of rock. And that's when the might of the cosmos is truly shown off, either on a regional or a global scale.
Returning to the massive Chicxulub crater-causing asteroid, the projectile that struck our planet was estimated to be roughly 10 kilometers (6.2 miles) in diameter - imagine a rock larger than the entire city of Seattle.
To make matters worse, asteroids travel at incredible speeds relative to Earth that seem incomprehensible to us mere mortals.
The Chicxulub impactor was estimated to be travelling at nearly 20 kilometers a second when it struck Earth (that's nearly 72,000 kilometers per hour, or about 45,000 miles per hour).
The incredible kinetic energy such a massive rock travelling at those speeds turns into explosive force once it runs into sufficient resistence, the incredible amount of friction causing the massive fiery ball of rock to superheat and essentially explode after hitting the ground (or water).
The ensuing fireball incinerates anything in the immediate vicinity, sending a shockwave rippling across the globe and flattening everything around it, a wave of scorching air setting forests that were far enough to escape the initial blast ablaze.
The massive explosion sends all sorts of debris from both the meteor and the Earth it struck into and out of the atmosphere, causing effects that can be measured around the entire planet.
The kind of chaos and destruction that such an event would bring is hard to even grasp - an entire continent effectively demolished, the globe trembling from the impact and the ensuing earthquakes, forest-clearing firestorms, the globe soon plumetting into an effective "nuclear winter" from the smoke and ash enveloping the planet.
While the Chicxulub was primarily a land impact, an impact in the middle of an ocean would vapourize an immense amount of water (and all the life within it) and cause tsunamis of unbelievable power to ripple around the globe, with the increased moisture in the atmosphere altering the climate for years to come; a glacier strike would act quite similarly, and a major impact on a land glacier would potentially raise global sea levels by drastic amounts.
The devastating extinction-level event the dinosaurs experienced was not a one-time thing however, as thus far, five such mass extinctions on that scale have been widely recognized as occurring in Earth's more "recent" history (the last 500 million years), and the Chicxulub crater isn't even the largest of its kind that has been confirmed as an impact site.
That honour instead goes to the Vredefort crater in South Africa, which is largely eroded away and is currently some 160 kilometers (~100 miles) in diameter, but is estimated to have been at least 180 kilometers across initially and possibly as large as 300 (~185 miles), which would make it twice the size of the dinosaur killer. That crater is estimated to be some two billion years old and caused a mass extinction of its own far before any dinosaurs had ever roamed the Earth let alone humans.
There is also a very strong possibility the Deniliquin structure, a buried feature found in New South Wales, Australia, is another impact site that is larger than both the afforementioned sites, stretching nearly 520 kilometers across (~320 miles). It's potentially the cause of the Late Ordovician glaciation and mass extinction event which began an estimated 445 million years ago, but the site has yet to be drilled to be definitively confirmed and could also be the cause of an even older extinction event.
Should it be proven correct which mapping and magnetic data suggests it is, the Deniliquin crater would be more than three times larger than the Chicxulub site, bringing with it an apocalypse of unimaginable proportions.
Likewise, mapping data has unearthed a similarly apocalyptic crater site over 1.5 kilometers (~1 mile) underneath an Antarctic ice sheet.
This likely impact site has a diameter over 500 kilometers (~310 miles) across, and some have suggested it to be roughly 250 million years old, which associates it as a likely cause of "The Great Dying", a period which saw nearly 90% of life on Earth eradicated. Unfortunately, given its location and the costs involved, it's unlikely any drilling to definitively prove the crater is from a meteor impact and when exactly it happened will occur anytime soon.
At a glance, the last five academically accepted mass extinction events (defined as roughly three quaters or more species are lost in a "short" period of time) that have occurred in the past 500-million years are as follows:
The Late Ordovician or Ordovician-Silurian Extinction, which happened roughly 445 million years ago. 70% of life is estimated to have been wiped out; the afforementioned Deniliquin structure in Australia is a possible candidate as a driver of this extinction, which began with rapid glaciation before the glaciers abruptly receded (such a rapid cooling could occur from a massive impact, with widespread fire following the impact along with material ejected from the blast smothering the atmosphere and restricting sunlight for an extended period, similar to a "nuclear winter")
The Late Devonian Extinction, which is actually a collection of several extinction events roughly 360-385 million years ago; the timespan of this extinction "event" has estimates ranging from 500,000 to 25 million years, calling its placement as a mass extinction like the others listed into question; the Siljan Ring in Sweden, an impact site spanning roughly 52 kilometers (~32 miles) is thought to be the cause of one of the extinction events that as a whole comprised the Late Devonian Extinction event
The Great Dying, aka the Permian-Triassic or Late Permian Extinction Event, occurred 251.9 million years ago and resulted in nearly 95% of life being wiped out; rampant volcanic activity is thought to have caused the worst extinction in Earth's (known) history, however many scientists believe asteroid impact(s) are the more likely culprit, or possibly contributed/triggered other catastrophic events. The afforementioned Wilkes Land crater in Antarctica is a possible impact site associated with the event, though accurate dating of the site has yet to occur
The Triassic-Jurassic Extinction Event, or the End-Triassic Extinction, occurred some 201.4 million years ago and saw the dinosaurs take over in its wake; the cause of this event is still unknown, however high iridium anomalies suggest an asteroid impact is a strong possibility
The Cretaceous-Paleogene (K-Pg) or Cretaceous-Tertiary (K-T) Extinction Event, occurred 66 million years ago; the Chicxulub crater in Mexico is the impact site associated with the extinction of the dinosaurs
While the effects of each extinction are far more apparent, the causes of each are hotly debated and still very much unknown outside of the most recent event; for instance, while the Late Ordovician Extinction has clear evidence rapid glaciation followed by a subsequent swift deglaciation wreaked havoc on the planet, the catalyst for that glaciation is not so clear and there are plenty of theories to go around.
The only mass extinction with a clearly defined cause is the K-Pg or dinosaur extinction; however, strong evidence links asteroid impacts to all four other mass extinctions mentioned, and the consequences of such an impact are of course clearly demonstrated by the most famous extinction.
They are also linked to many more regional exterminations. For instance, the Manicouagan Reservoir in Quebec has a massive crater at its center that spans nearly 100 kilometers (62 miles) across that was formed by a meteor estimated to have been roughly 5 kilometers (3 miles) in diameter that wiped out virtually all terrestrial life in the surrounding area roughly 214 million years ago.
Even smaller meteor strikes however can have massive ramifications for any life on our planet that happens to be near its path.
Take a look at Barringer's Crater in Arizona, which has a diameter of just over a kilometer; a mere fraction of the Chicxulub site which has a diameter roughly 180 times wider.
This (relatively) tiny crater was caused by an impactor approximately 160 feet in diameter (that's about the width of a football field) with an estimated blast yield of 10 megatons of TNT, effectively the equivalent of 667 Little Boy atomic bombs (the bomb that flattened Hiroshima).
As you could imagine, anything in the surrounding area would have been wiped out instantly; had an asteroid that size fallen on a human city, not only would all inhabitants be dead, but virtually any evidence they ever existed would have been vapourized as well.
A direct hit on the ground is not the only kind of extraterrestial strike that can happen however, and this other type of impact is one that has been documented and studied in much more recent history.
An airburst occurs when an asteroid that contains a large amount of ice makes an unexpected visit to our world.
As the resulting meteor descends toward Earth, the friction forces generated between the meteor and Earth's increasingly thick atmosphere melt the ice and subsequently superheat the water vapour, which rapidly expands to the point that the meteor blasts apart in a powerful explosion.
In 1908, Russia narrowly escaped a devastating blow when such an airburst occurred in their territory.
On the morning of June 30th some 115 years ago, a meteor exploded in an airburst some 5-10 kilometers (3-6 miles) above the ground near the Tunguska River in Siberia.
The explosion generated a blast force estimated at 10-15 megatons of TNT - that's up to 1000 times more powerful than the bomb dropped on Hiroshima in 1945.
Despite the airborne detonation, the explosion still managed to flatten some 80 million trees across roughly 830 million square miles of forest.
Luckily, the Tunguska airburst happened over a very sparsely populated region in Siberia, and thus there were no confirmed human deaths as the result of the blast (although three possible deaths were later linked to the event from eyewitness accounts), however the massive explosion still devastated local wildlife and certainly would have caused carnage if it had occurred over a populated area.
As much as people like to think that meteors making it through Earth's atmosphere is rare, they are actually quite common, with thousands of small meteorites making relatively safe journeys to the ground every year, typically not causing any notable damage due to their miniscule size.
In fact, meteor showers commonly occur multiple times a year as Earth passes through different debris and asteroid belts, such as the Perseids and the Taurid meteor streams.
The Taurid streams in particular have been looked at as a probable source of major impacts in the more recent past; the rocky streams of debris are believed to be the remnants of a larger asteroid which has broken apart over many millennia and are currently the largest stream of matter in the inner solar system, making it of particular interest to our planet.
Earth takes several weeks to pass through this stream each year, resulting in annual meteor showers from September to November, which consist mostly of very small meteors burning up in the upper atmosphere. When the Earth's orbit takes it through more dense areas of the stream however, larger asteroids become a much more significant threat.
NASA currently estimates that an asteroid roughly the size of a football field hits Earth once every 2,000 years or so, with strikes from larger bolides occurring less frequently.
For an even more recent close call than the Tunguska airburst, Russia was once again buzzed by a meteor in 2013, this time over Chelyabinsk Oblast, which unlike the Siberian wilderness in 1908, was not no sparsely populated.
This time the meteor measured a much smaller 66 feet in diamater, and thus exploded nearly 30 km (18.5 miles) above sea level, generating a blast yield equivalent of 400-500 kilotons of TNT (roughly 26-33 times more powerful than the afforementioned Little Boy atomic bomb).
Luckily with the air burst occurring so far above the surface and with a smaller meteor, no one was killed as a result of the Chelyabinsk airburst, yet nearly 1,500 people sought medical attention in the aftermath due to indirect effects of the explosion's shockwave (mainly from broken glass being blown into buildings and vehicles) and over 7,200 buildings across six cities were damaged.
With both of the events that have happened in more modern history, our planet has been lucky - but what happens when an event such as the Tunguska air burst occurs over a populated area? Or, when a larger meteor manages to make it all the way down and impact Earth's surface directly?
It's hard to imagine the devastation and global impact such an occurrence would have in modern times, yet our ancestors have undoubtedly had to deal with similar events before given anatomically "modern" humans have existed for over 300,000 years.
What may be surprising however is that an overwhelming amount of evidence points to a cataclysmic impact (or possibly, multiple impacts) occurring nearly 13,000 years ago; although its devastastion wasn't quite on the level of the five "major" extinction events talked about above, the time period saw an estimated 80%+ of megafauna (large animal) species go extinct and our human ancestor's populations were decimated to the point humanity nearly followed suit.
The Younger Dryas, the period between 12,900 and 11,600 years ago that saw this megafauna extinction event, is the topic of the next piece in The Human Story. Check back soon to find out all about the devastating conditions that humanity barely managed to survive - and how our ancient ancestors may have been far more advanced than modern views would have you believe.
