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Over 60 million years after their previous visit, our time traveling aliens have returned to witness a truly magnificent and defining period in Earth's history, one which will shape the future of life on this planet and leave behind some of the most exciting paleontological relics ever discovered, the last ice age. Of course, these aliens are no strangers to Earth's dynamic changes throughout history. They've already witnessed great extinction events, extreme weather lasting for millennia, and the evolution of increasingly complex life forms. But this visit is about to give our aliens a lesson in the extremes that life on Earth can endure.
Over 100,000 years ago, many of our planet's ecosystems were reshaped by colossal ice sheets, piercing polar winds, and barren landscapes. A glacial age where frigid temperatures lasted for millennia. And with the end of this period will come with the mysterious disappearance of many of its most iconic species for reasons we are still struggling to comprehend to this day. I'm Alex McColgan and you're watching Astron. Join me and our aliens in this video as we thaw out the mysteries of the last ice age, uncover the science of how it began, and glimpse into the lives of the magnificent creatures that
evolved to thrive in this frozen world, and yet ultimately failed to make it out alive. This ice age is not the first our aliens have witnessed throughout Earth's history. We've actually had five major ones in total. So, what do they have in common? An ice age occurs when the Earth experiences cold temperatures for an extended period of time, millions to tens of millions of years that is. This causes the Earth's surface to be taken over by large ice sheets and glaciers. The ice age we are talking about started around 2.6 million years ago with the dawn of the Pleistocene. And you may be surprised to learn that we are still in it.
Any ice age can feature both frozen glacial periods and warmer interglacial periods. And it is, in fact, the latest interglacial period that we've been experiencing for the past 11,000 years. So, when people refer to the last ice age in popular culture, they often mean the last glacial period, which came right before and lasted from 115,000 to 11,700 years ago. It may also be surprising that the average temperature during the last glacial period was only about 6° colder than today's global average. However, a global change in temperature can have profound effects even when the difference is in the single digits. When we think about a 6° global drop in temperature, we mean 6° worth of thermal energy being lost from all our oceans,
land masses, and the atmosphere combined. During our last glacial period, much of Europe and North America was dominated by two major expanses of ice, the Laurentide Ice Sheet and the Fennoscandian Ice Sheet. Because so much of Earth's limited water supply was locked away in these ice sheets, the average sea level was much lower and the land mostly consisted of tundra-like vegetation spread across dry, grassy plains. There is no single factor that explains why the Earth was plunged into but a lot can be resolved by looking at its orbit at the time.
Last century, the Serbian scientist Milutin Milanković hypothesized that long-term collective changes in the Earth's position relative to the Sun are a strong driver of Earth's long-term climate and could be used to explain how glaciation periods or ice ages are triggered. Milanković studied these three types of Earth orbital movements and how variations in these movements can change the amount of solar radiation that reaches Earth's surface. There's already a video dedicated to Milanković cycles on our channel, but here's a really quick recap of what they are and what they mean.
The first is the eccentricity of the Earth's orbit. When the pull of gravity from Saturn and Jupiter is stronger, Earth is forced into a more elliptical orbit, which happens around every 100,000 years. During times of highly elliptical orbit, Earth sees the greatest variation in the length of each season with summer lasting longer than winter. Any planetary orbit features aphelion, when the planet is furthest from the Sun, and perihelion, where it is closest. However, a highly elliptical orbit means that the Earth's aphelion in July is at its furthest distance from the Sun, so
the amount of solar radiation that reaches Earth during this time is around 23% less than during perihelion in January. The result, warmer, shorter winters for the northern hemisphere, and cooler, longer summers. The second Milankovitch cycle concerns the obliquity, or tilt, of the Earth on its axis. The more tilted the Earth, the more extreme the seasons, and this varies on a roughly 41,000 year cycle. So, when Earth is less tilted, the difference between seasons is mild enough that the summer can't melt the winter ice, which could allow it to accumulate and bring about an ice age.
The third cycle is known as axial precession, or wobble. Like the name suggests, the Earth can wobble upon its rotational axis as a result of the gravitational influences from the Sun and Moon, which cause the Earth to bulge outward slightly at the equator, rather than maintain a perfect sphere. This movement varies on a 26,000 year cycle, and makes the contrast between seasons more or less extreme, depending on when perihelion occurs in each hemisphere. For example, modern-day perihelion occurs during the northern hemisphere's winter, meaning that their seasonal fluctuations are less extreme than for the southern hemisphere.
The combination of all three cycles works to influence the Earth's long-term climate, and they have been pretty reliable factors in predicting the major ice ages so far. However, shorter-term cycles are also important, and can enhance or weaken these large-scale effects. Two major ones that occurred throughout the last ice age were the Dansgaard-Oeschger events, associated with sudden warming, and Heinrich events, causing rapid cooling. So, here comes the big question, And it is indeed big, as you'll see in a moment. How did the creatures roaming on our planet adapt to these changes? What did they look like? How did they live?
We mentioned that much of the last ice age occurred during the Pleistocene epoch, which spanned from 2.6 million to around 11,700 years ago. The ice age was a time when megafauna walked the earth. And the word mega is no overstatement. Some of the largest of these creatures weighed 4,500 kg. There are a few theories as to why everything tended towards the gigantic during the ice age, which involved different animal strategies for conserving energy. For example, Bergmann's rule describes how for animals that produce their own body
heat, like mammals, the colder the environment, the larger their body size. This is because larger-bodied mammals have a lower surface area to volume ratio, which prevents them from losing heat easily to the surroundings. So, this might partly explain why so many large and imposing species evolved during the ice age. Colder temperatures meant more pressure on animals to minimize heat loss if they wanted to survive. Although a general strategy was to be big during the ice age, the diversity of species at the time proves that there were lots of different ways to do it. Let's start with the most famous one. Woolly mammoths are a picture of the ice age itself for most of us.
A towering, dominating presence marching through great snowdrifts, seemingly impervious to the cold. But the reality was perhaps slightly different from what we imagined. Woolly mammoths weren't actually much bigger than modern-day elephants. Measurements made from their skeletons tell us that their shoulder height was 3.5 m, whereas some of the larger male African elephants today can reach heights of 4 m. Although they may have been a similar height to the elephants we know, they did have some key physical differences. Woolly mammoths aptly had warm, double-coated fur separated into a thick underwool and a layer of longer outer hairs.
They also differed in their proportions with longer bodies and shorter legs than modern elephants. Paleontologists think this was so they didn't have to stoop so much to graze on tundra-like vegetation, which is typically shorter than the trees and bushes of the savanna or rainforest. Further aiding their insulation was a layer of fat up to 9 cm thick and small, hair-covered ears to prevent heat loss. Finally, they had a raised bump on the top of their heads, which contained large sinuses. This may have helped them to humidify and warm the air as they were breathing, a useful skill for Arctic conditions.
Despite our best efforts to resurrect them, most recently with the woolly mouse that shared a mammoth gene for body fat, woolly mammoths are sadly extinct. But they didn't go extinct all at once. In fact, it's now accepted that a population of 500 to 1,000 woolly mammoths survived on Wrangel Island until around 4,000 years ago. That's 1,000 years after the Great Pyramids of Giza were built. Scientists think that the mammoths made it to the island across the land bridge of Beringia, which used to connect Alaska and Siberia before it was submerged under the Arctic Ocean.
Now, onto some of the more obscure creatures of that glacial period. The glyptodont. Their name means carved tooth in Greek owing to the wide grooved structure of their teeth, which was adapted for them to grind on the tough vegetation of the land they grazed. They were a large cumbersome creatures weighing up to two tons and walking on elephant-sized legs across the Americas. Their bodies were protected by a huge turtle-like shell or carapace giving them a similar look to an armadillo, although they couldn't roll up into a ball. So, you can think of them as a distant relative of the armadillos that behaved more like a land tortoise or a hippopotamus.
Quite the wacky combination evolution-wise. Our aliens would be forgiven for thinking that these creatures don't get around much, but recent studies testing the strength indicators of the glyptodont's forearms have revealed that they bore most of their weight on their back legs and they may have even been able to stand on them bipedally. This conjures up some even crazier images. A glyptodont standing to deliver a blow with their armored tail or to reach a high food source and proves that these creatures were not to be messed with. While mammoths and glyptodonts might have been the titans of their time, they
are not around today. Evolution ultimately replaced them and honestly, that's a terrifying thought. That moment when you realize your job could disappear, You could be replaced and you don't know what else you're even qualified to do. But, unlike ancient creatures, we can adapt to a changing world thanks to the sponsor of today's video, Tripleten. Tripleten is a flexible boot camp that helps you switch to a new in-demand career. Their beginner-friendly programs are incredibly effective. 82% of graduates get hired within 6 months of completing the course. Why? Because students don't just study theory, they work on real projects with real companies, building a portfolio they can show to future employers. And if you're scared of taking a risk, there's something
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The late Pleistocene sloths included 27 genera in four families and an unknown number of species. These were great dispersers and roamed across the Americas, even reaching the Caribbean islands in the middle Neogene before the Isthmus of Panama formed. This is probably part of the reason why they were able to diversify into so many species since they were exposed to many different habitats. Through time, the sloths tended towards larger sizes, and by the late Pleistocene, nature had given birth to a group called giant ground sloths.
Within this group, Eremotherium combined the height of a giraffe with the bulk of an elephant. And the first described sloth fossil, Megatherium americanum, had an estimated body mass of 3,800 kg. Our modern-day sloths are puny in comparison. Their Pleistocene ancestors were around 950 times heavier. Far more widespread, and if the relics they've left behind are anything to go by, they got up to a lot more. In a study from 2020, paleontologists reported finding the remains of at least 22 Eremotherium sloths of various ages in the sediments of Tanque Loma on the southwest of Ecuador.
It's likely that these sloths got caught in a shrinking watering hole during a drought and died from disease or starvation as the drought killed off their food sources. But, weirdly enough, this autopsy report tells us a lot about how these animals lived, and that's where scientists get excited. Think about it. We know that they congregated at watering holes, suggesting that they were sociable animals, and that they were wallowing in the water to escape the sun and insects. Though the last glacial period was dominated by ice sheets, they didn't cover the entire globe. Tropical regions like Ecuador see warmer seasons when animals would have needed a cool refuge.
The sloths' wallowing behavior is shared with many large African mammals alive today, like hippos or rhinos. So, it turns out that the Pleistocene watering holes were still the bustling ecological hubs they are today. So, we know where they hung out, but what else were the giant ground sloths getting up to? Mar del Plata in Argentina is home to several paleo burrows, which have been discovered intermittently over the past century. 42 of the largest burrows were dated back to the Pliocene or late Pleistocene and reached 5 to 6 m below the surface. At their largest, they are 1.8 m wide and 40 m long.
Several mammal candidates were considered as the possible builders for these structures, but scientists now think that the culprits were the Glossotherium and Scelidotherium ground sloths, and there are several reasons why. The first clues were the arm bones of these sloths, which were designed to form a shovel-like structure with unusually long second and third fingers, making them well adapted for digging. The bones were strong, too, designed to withstand intense bending forces similar to those experienced by modern galloping mammals. From further detective work on their skeletons, paleontologists estimated that these ground sloths' center of
gravity was found above their hind feet, which suggests they too could achieve a bipedal posture. This is a major requirement for digging as your arms have to be able to exert pressure on the soil you're trying to dig, rather than support your body weight all the time. And the final clue? Well, this one quite literally caught the sloths red-handed. See, there were several claw marks on the sides and roofs of the burrow that had been perfectly fossilized with the tunnels themselves. So, paleontologists just had to match up these marks to the hand skeletons of the sloths, and just like that, it was a perfect fit. So, we can be pretty confident that we found the burrowers. But, considering these ground sloths weighed between 800 and 1,200 kg, this
behavior is incredible, and gives us real insight into the kinds of pressures they must have been facing. Scientists have proposed that the sloths may have relocated underground as a way to insulate themselves against the cold, or shield themselves from the heat, depending on the climate at the time. It's also been suggested that the sloths were trying to escape predators, which really makes you wonder what kind of animal would want to take them on. Most likely, a saber-toothed cat or giant short-faced bear. As our aliens have watched these big, tough creatures brave weather extremes, mega-sized predators, and shifting populations, they are excited to see them emerge into the next epoch with
their innate knack for survival. Except, that's not what happened. Almost without warning, they vanished at the end of the Pleistocene. Between 72% and 88% of these large-bodied creatures were lost from Australia and North and South America alone. But, how? Why? Well, this topic has been intensely debated among human paleontologists for nearly a century. Some suggest that natural climate change was to blame, as the dawn of the interglacial period meant that sea levels started to rise, cutting off the
land bridges and melting the ice sheets that species needed to reach more thermally suitable habitats. However, we've seen this explanation isn't a perfect fit as some groups like the Wrangel Island mammoths survived far beyond this transition. The other major theory was first proposed in the 1960s and brings us to the next point on our ice age journey. Humans. For the first time ever during their visits to Earth, our time traveling aliens are gazing down on our very own ancestors. Homo sapiens evolved around 300,000 years ago, migrating out of Africa to colonize regions around the globe. This means they've lived through a fair chunk of the Pleistocene and shared the land with other ice age creatures of the time.
So much so the paleontologists and our aliens are wondering whether we were responsible for the megafauna extinctions at the end of the Pleistocene. Could this be true? Could we have taken on a great woolly mammoths and giant ground sloths and won? To answer these questions, the aliens are taking a closer look at our ancestors of old. They may have evolved 300,000 years ago, but it wasn't until the late Paleolithic or between 50,000 and 10,000 years ago that Homo sapiens started to experience real cultural development.
Hunter-gatherer culture was at its peak and human burial practices started to spread between multiple human populations. So the paleontological relics from this time period are unusually good. We started to use more diverse tools, made personal decorations like pendants, and invested more energy in activities that went beyond just surviving. For example, cave art was used as an outlet for humans to interpret the world around them, and many of the images they created can still be seen today. One of the most impressive, described as the Sistine Chapel of prehistory, was discovered in Lascaux Cave in Montignac, France. In just a small cave, over 500 painted
and 1,500 engraved images have been found that were created up to 22 and 1/2 thousand years ago. From these images, you can see that the aspiring human artists mostly focused on animal subjects, perhaps as a testament to their hunter culture or their close relationship with wildlife. Either way, we know our ancestors were aware of the Ice Age megafauna around them, but were they capable of driving them extinct? We've talked about the rapid improvements to tools during the late Paleolithic, and this would have massively improved our ability to hunt.
One brave Homo sapien versus a woolly mammoth is unlikely to end well, but a whole group of them armed with sharpened spears that can throw them up to 40 m, that creates a more even playing field. One particularly skilled group of hunters were the Clovis, the ancient ancestors of Native Americans, who had distinctively shaped spearheads or Clovis points. The fine craftsmanship of these weapons suggested that these people were expert hunters capable of taking on the local megafauna of North America where they lived.
Another point of contention was the fact that within a few thousand years of the Clovis people arriving in North America and spreading across the region, the megafauna had gone extinct. So, we have to wonder whether it was the intense Clovis predation that led the last populations of these animals to collapse. Either that or the timing is a pretty big coincidence. A study last year sought to investigate this by analyzing the only known Clovis individual, the 18-month-old Anzick child, which was first discovered in 1968 in western Montana.
The bones of the child are thought to be 12,700 years old, and a stable isotope analysis was used to create the protein diet of its mother. Researchers found that mammoth contributed around 40% to the maternal protein diet, and was similar to the diet of a mammoth specialist predator, the scimitar cat. This lends support to the theory that the Clovis people, with their effective longer-distance weapons and hunting strategies, were at least partially responsible for the rapid megafauna extinctions in North America.
However, we are still lacking in paleontological remains for these people, so we can't say that the conclusions drawn from the Anzick child would be the same for all Clovis hunters. But, if this evidence is anything to go by, our aliens would be right to want to keep an eye on the suspicious activities of Homo sapiens. And what about other regions? Megafauna suffered heavy extinctions in Australia, too. Like North America, Australia lost 85% of its large mammal species right around the time that humans became established there.
Seems like whenever humans arrive, things start to collapse. Paleontologists have some nifty tricks to piece together the timeline for this collapse, like measuring the levels of fungal spores, which are commonly produced in the dung of herbivores as a proxy for megafauna populations. So, the more spores, the more mega-sized herbivores there were at the time. From this data, they found that megafauna populations collapsed within 4,000 years of humans arriving. Although there were environmental changes in the tens of thousands of years before the collapse, including wildfires and a transition from woodland to shrubland, humans were probably the straw that broke the mega camel's back, and their hunting pressure was too
intense for these animals to recover. Large mammals, like the megafauna, typically have slow population growth and don't reproduce often. So, even low-intensity hunting would have a big impact. All in all, we're probably not giving the friendliest first impression to our time-traveling aliens. We seem to be at least partly responsible for the loss of lots of other ice age species, and it's not only the megafauna that were affected. Another mysterious disappearance in the late Pleistocene were the Neanderthals, who vanished around 40,000 years ago. Neanderthals were the first humans to survive a cold glacial ecosystem with clever adaptations to do so.
They were short and stocky, reaching maximum heights of around 160 cm. They had large noses with a high bridge, creating a larger nasal chamber which humidified the air as they breathed, a similar adaptation to the mammoths. Contrary to popular belief, the Neanderthals had quite a sophisticated culture. They were also partial to cave art, ornamental objects, and burial rituals, just like Homo sapiens. So, with all these abilities to help them survive the extreme climate, how did they come to meet their end? You guessed it. We might be to blame for this one, too. Paleontologists think that we either out-competed them, or they were absorbed into our populations, which happened to be larger at the time.
In fact, most people of European or Asian descent share between 1 and 2% of their DNA with Neanderthals, which would support the second theory. As for competition, the latest data suggests that Neanderthals and modern humans coexisted happily for up to several thousand years in Europe. It is possible that in some regions where resources were scarce, the pressure was greater, and we did compete more with our evolutionary cousins. Whilst their stocky bodies may have helped them produce and retain heat, this also made them worse at conserving energy. With bodies that were costlier to run, it was probably easier for the more energy-efficient Homo sapiens to move in and take over.
Like many debates emerging from this time period, there's no simple answer for the Neanderthals' disappearance, and the situation varies from place to place. Though we may have been the better competitor, the Neanderthals get a bad rap, and every new discovery adds to our appreciation of the complex culture, language, and tools they left behind. There's no doubt that the last ice age brought about huge developments that would change the course of Earth's history forever. Changes that our time-traveling aliens had come to witness. Despite the unpredictable nature of this era, plenty of species were able to thrive during both glacial and interglacial periods, diversifying, evolving huge body sizes, and developing innovative ways to combat
climate extremes. Though not everyone made it out alive, it's amazing to think that Homo sapiens once shared the land with these weird and wonderful species, human and animal alike. But perhaps the more concerning question is whether this will happen again. We've already touched on the fact that the Earth has seen five major ice ages throughout its history, and this most recent one is still ongoing. Is another glaciation event looming in our planet's future? We've mentioned Heinrich events, which occur on more short-term scale to the Milankovitch cycles, and can cause periods of cooling around every 10,000 years.
They happen when large amounts of ice are discharged into the ocean, which produces a global footprint that has historically made regions of North America and Eurasia become colder and drier. Data on the subsurface ocean temperatures has revealed that warming usually happens in the hundreds to thousands of years before these ice loss events, as this is what destabilizes the ice sheet and promotes its breakup. This warming contributes to a weakening of the AMOC, and both these factors act as triggers for Heinrich events. We've recently made a video on the Aimak over on Astrium Earth, which you can check out for more information.
But the point is that we are seeing both of these signs happening now. So, they could be warning signs a Heinrich event is coming. If it does, then it could cause enough cooling to trigger another glaciation period. Though it's hard to say for sure. It would probably have to coincide with another Milankovitch cycle to cause Pleistocene levels of ice. But either way, things could get frosty. If we did experience another glaciation period, I wonder which species would survive. Would they have time to adapt? Or would temperatures plummet before they had the chance? Can Homo sapiens survive yet another age dominated by ice? Or are we in danger of being wiped out by something better adapted than us? As our aliens pack their notes
away and leave the ice age behind, I'm sure they're left impressed by the diversity of life that lived through this epoch of Earth's history. Though many of these creatures are now just remnants of the past, they still capture our curiosity with their skeletons, burrows, and even burial sites, hinting at a world where, at least for a while, mankind lived alongside towering beasts and human kin navigating the same raw, unforgiving wilderness together. What kind of planet and inhabitants will our aliens meet when they come back again next time, in our future? Thanks for watching. If you've been enjoying Astrium's videos and want to help keep this channel thriving, I want to ask you to take less
than a minute to check out the Astrium Patreon. It's not just ad-free videos, but it's a way to make Astrium's videos less reliant on sponsors and algorithms. The link is below. Your membership directly helps ensure that future videos can stay independent, high-quality, and consistent, created for curiosity, not clicks. Thanks so much for considering it. I'll see you next time.
