The Big Chill: When 96.7% Of Humans Died

Imagine waking up tomorrow to find out an unstoppable natural disaster is about to wipe out the entire population of the human race. Or to be more specific, 96.7% of it. Thankfully, it doesn’t look like that’s going to happen to us anytime soon, but that isn’t to say it hasn’t happened before. These near-extinction circumstances were a reality for our ancestors at one point in history. So, let’s rewind the clocks to that time 96.7% of humans died.

There are around 8 billion human beings alive today. With such an enormous population, it’s hard to imagine that we were once an endangered species. But it’s true: at one point, we were one turn of bad luck away from being wiped out completely. But, thanks to a little sprinkling of good fortune and the impressive intelligence of our ancestors, we’re still here today.

The Big Chill: Marine Isotope Stage 6

195,000 years ago, the world was almost unrecognizable compared to what it’s like today. There were no cities or cars, no cell phones or fast food restaurants and there was certainly no Wi-Fi. But the most significant differences between Earth in 2020 and Earth 195 millennia ago were in the temperature and climate. Back then, Planet Earth was starting to get very, very cold, because of something called the Big Chill, or if you want to get all scientific, Marine Isotope Stage 6.

Marine Isotope Stages are alternating warm and cool periods in the history of Earth’s climate. These varying stages are assigned higher numbers the further back in Earth’s history they occurred, and are measured by scientists studying data from deep sea core samples.

The levels of an isotope of oxygen, known as oxygen-18, in a sample reveals information about how prevalent ice sheets were at the given time. The more oxygen-18 absorbed by the sediments around the world, including the bottom of the oceans, the more severe glacial build-ups of ice were in that period!

The period we are currently living in is classed as Marine Isotope stage 1, marking a nice and toasty segment of Earth’s history. Marine Isotope Stage 6, meanwhile, lasted from 195,000 years ago until 123,000 years ago, and samples from the period show high levels of oxygen-18.

With this info, we know Earth was going through a particularly chilly time, which experts refer to as a "glacial period". Our ancestors, meanwhile, probably referred to it as really bad news. At least, they would’ve, if they understood modern languages.

The temperature, which had previously been warm enough to support plant and animal life over great expanses of the Earth, plummeted. Compared to our modern-day global averages, the global temperature was 10 degrees Celsius, or 18 Fahrenheit lower! Needless to say, that kind of chilliness had some serious effects on the world.

This freezing weather triggered drought conditions so severe that vast stretches of Europe, Asia, and much of the African continent were virtually uninhabitable. Neither plants nor the creatures that ate them could survive, and life was forced into rare, hospitable pockets of warmer land, if they were lucky enough to find them.

But in certain parts of the landmass we know as Africa today, conditions were just about temperate enough for life to cling on to, and as it happened, that’s exactly where all the humans were. However, you wouldn’t find any kingdoms, cities, or even towns. For these things to exist, you need a lot of resources, for one thing, and during a glacial period, the circumstances made the emergence of larger, settled communities unviable.

Human Origins In Africa

For the homo sapiens that were around, Africa was home. In fact, humanity didn’t expand beyond the borders of Africa in large numbers until around 70,000 years ago. Which makes sense in light of the small size of the population and scarcity of available resources at home and elsewhere to support long-distance exploration.

At this time, human communities were small, nomadic, and spaced out, and the total global human population was tiny, even in good times. For much of their existence, ancestors of modern humans, including populations of non-homo sapiens like homo erectus and homo neanderthalensis, maintained this trend of very small populations.

The entire human breeding population hovered between 10,000 and 30,000 people starting at about 400,000 years ago. For perspective, the number of humans at this time was comparable to the number of polar bears on Earth today.

This human population size isn’t believed to have begun substantially expanding for another 350,000 years. But somewhere in the middle of all that, the Big Chill dawned, and brought those numbers to breaking point.

When the Marine Isotope Stage 6 was in full swing, winter was no longer coming; it was here, and it was nasty. Humanity’s ancestors so far had enjoyed a rather warm existence hunting and gathering under the African sun, but now their very survival was thrown into question.

With huge amounts of the Earth’s liquid water becoming trapped in glaciers, the deserts expanded, leaving almost everywhere barren, cold, and dry. With habitable land gradually becoming scarcer and scarcer, early humans were left with only two options. Either sit it out and freeze or starve to death, or pack up and run.

Unfortunately, a significant portion of existing humans didn’t have the ability or awareness to move in time, or were simply too far from habitable hotspots, and perished. Many other humans split up into smaller, less-stable populations looking for more habitable lands. Only a lucky few reached their destinations.

The Biggest Population Bottleneck

With danger and death at every turn, at the most challenging points of this period, the total human population is estimated to have dropped as low as 600 people. Marine Isotope 6 almost wiped out the entire human population, which is thought to have sat at around 18,000 before the Big Chill really hit.

By our best estimates, a staggering 96.7% of the human population died out, leaving 3.3% remaining with the weight of humanity’s future on their shoulders. Considering how small the population had already been beforehand, humanity was facing extinction before it had even gotten properly started.

That small band of humans that did survive managed to escape the expansion of the arid deserts and glaciers by moving down to the south African coastline. In these more forgiving climates, our ancestors could put their already-impressive intellect to good use, taking advantage of the available resources. In fact, some experts have even suggested that the intelligence demonstrated in our ancestors’ abilities to move around and adapt was what allowed us to survive against all odds.

Put bluntly, when faced with apocalyptic scenarios, it pays to be smart. The greener, or bluer, pastures the remaining humans moved to were always close to the sea, which proved a vital factor in the survival of the species.

So, why is the sea so special? For starters, the ocean in these regions had alternating warm and cold currents, which meant it was absolutely teeming with marine life. This included nutrient-rich foods like sea snails alongside the occasional seal and whale.

However, no single food source was more significant than shellfish, which thrived along the South African coast. These tasty marine treats were an excellent source of protein for the humans, and there were plenty of them to go around, all year long!

Considering how scarce food was everywhere else, some experts even suggest that, at this point in our history, the sea was responsible for the survival of humanity. But while there’s certainly some truth in that claim, the sea wasn’t the only source of food in these temperate lands. There was an incredible diversity of plant life to be found as well.

The region featured an abundance of plants adapted to survive through the increasing cold temperatures using underground storage organs which contained high-quality carbohydrates, making them a great energy source. And when the weather permitted open, grassy plains to arise, our ancestors would go hunting large mammals like antelope.

All in all, as far as post-apocalyptic hideouts go, humanity really struck the jackpot with this area of South Africa. Compared to the arid wastelands further north, the coastal regions of the south were like the Garden of Eden. Those living there had a plentiful, varied and nutritious diet, and were in the perfect environment to start rebuilding the population.

It wasn’t all fun and games, though. The smaller populations were far more susceptible to diseases and environmental disasters. This meant that even among those who found refuge, the dispersed populaces of entire areas could be wiped out in the event of something like a virus outbreak or flood.

Plus, unfavorable genetic traits, like hereditary illnesses, can be passed on rapidly in smaller gene pools. With so few humans remaining, this was a very real threat to humankind’s survival. With so many odds stacked against them, it’s pretty miraculous that our hardy ancestors survived in their small groups, even once the worst of the Big Chill was over.

But the Chill didn’t come and go in a few months, or a year or two, or even a decade. The Big Chill of Marine Isotope Stage 6 lasted for more than seventy thousand years! Countless generations of humans lived and died during this unforgiving stage in Earth’s geographical history, with many never knowing what a warm summer’s day felt like.

Of course, the humans who lived during these cold, dark days didn’t know any different, which was probably for the best. But just because survival was the main focus day-in, day-out, that didn’t mean it’s all they thought about. We need only look to the caves that many of our South African survivalist ancestors called home for proof of that.

The Survivors Of The Big Chill

The human survivors of the Big Chill were a heck of a lot brainier than you might imagine, and not just because they were smart enough to live down south! In fact, their creative thinking and reflection is thought to have contributed significantly to their ability to thrive in spite of the challenges they faced.

Along the Klasies River in South Africa, there are a series of caves that were once home to some of those six hundred-or-so survivors of the Big Chill. One of these caves, given the slightly underwhelming name PB13B contains artefacts that suggest huge leaps in human cognition were made by our ancestors who resided there.

Evidence from the cave shows that they used the shellfish they hunted not only as a tasty food-source, but also as decorations, keeping hold of shells purely for their beauty. These decorative shells paired nicely with their love of carving and early paintwork, usually using iron pigments and animal fats.

The cave-dwellers would also treat their weapons and tools with fire, making them stronger and more effective. Before the discoveries in the PB13B cave, this method of heat-treatment was believed to have originated in France only 20,000 years ago.

As it turned out, our clever old ancestors were about 100,000 years ahead of the curve. With the advanced intelligence on show, it’s highly likely that the ingenuity of survivor groups like these contributed to their ability to survive the Big Chill.

Or, quite possibly, the toughness of their circumstances forced them to adapt intelligently more than ever. After all, they say necessity is the mother of invention. Whichever way around it was, though, without their impressive intellect, none of us would be here to learn about these tough survivors today!

You might have noticed that I’m referring to these survivors as our ancestors, and this isn’t just a generalization. With the severity of the Big Chill’s decrease in human populations, there’s a high chance that every single person you’ve ever met, or will ever meet, shares ancestors with those 600-or-so survivors.

This is because, following the catastrophic events of Marine Isotope Stage 6, the human population "bottlenecked". With population bottlenecks, there are two potential paths. Either the species goes extinct, or it recovers, albeit with greatly reduced genetic diversity. With even a slight shift in the variables, humanity might never have surpassed this bottleneck, becoming nothing more than another blip on the radar of Earth’s natural history.

In this case, thankfully, humanity recovered, but the way in which we survived raises an interesting point. Being that we’re very likely all descended from this merry band of survivors, it means our genetic diversity is relatively minimal compared to other animals.

Had this Big Chill not occurred, and had a more genetically-diverse range of humans continued to exist, we may never have had such a strong imperative to pull together in larger communities.

The differences between our ancestors and other, slightly genetically different groups of humans may have proven too great to overcome. There may even have been a state of constant war between different types of humans, had a wider variety survived. And who’s to say our ancestors would’ve won, and not been wiped out by others whose genetics afforded them greater strength or increased intelligence?

Without needing to unite as one in the face of near-extinction, civilization may never have arisen, at least not in the way we understand it. But, as we know, civilization did arise, because we were able to work together. With this narrow escape in our shared genetic history, it seems human-to-human connection really is in our blood. Perhaps that’s why socialization is so important to us.

But what if the further we stray from seeing humanity as one big family, the greater the obstacles to our future become? After all, the entirety of humanity was once encapsulated in a small group of 600, fighting for our species’ survival, and we’re all descended from them.

Early Human Migration Out of Africa

So where did humanity go once the Big Chill was over? 70,000 years after the glaciers expanded and humanity was knocked to its knees, the ice began melting away and life returned in spectacular fashion.

Perhaps fed up of being stuck in the same place for over seven hundred centuries, though more likely through the opening of new food opportunities, the early humans started to move out. As far as we can tell, they first expanded out of East Africa and into Asia before spreading out across the globe.

But it wasn’t an easy ride for humanity, and plenty more disasters struck along the way. Like the Toba supervolcano eruption 75,000 years ago, which spewed enough noxious material into the air to largely block out the sun for years, killing off countless human communities in the process.

We faced another ice age too, but survived once again by heading to the sunny southern regions and using our intelligence to adapt. Despite a seemingly endless barrage of challenges, humanity repeatedly triumphed over extinction.

It took until 1804 CE for the population to finally reach the milestone of 1 billion people, and thankfully, or unfortunately, depending on your perspective, our numbers haven’t shown any signs of slowing since.

But whatever your general view of humanity, one thing remains true. Without these early humans intelligently adapting to life in the hardest circumstances imaginable, and eating a lot of shellfish, humanity would have been wiped out 195,000 years ago. You wouldn’t be reading this article right now, or browsing on the web, or even existing at all.

These hardy survivors are the real heroes of the human race and deserve to have their story told. The story of the time humanity was saved by a winning combo of our big-brain smarts and the big blue sea.