Over 60 million years after their
previous visit, our timetraveling 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, we'll
cover the mysterious disappearance of
many of its most iconic species for
reasons we are still struggling to
comprehend to this day.
I'm Alex Mccoan and you're watching
Astramm. Join me and our aliens in this
video as we thor 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're talking about started
around 2.6 million years ago with the
dawn of the pletos scene. 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
Fenoscandian 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 these
frigid conditions, but a lot can be
resolved by looking at its orbit at the
time. Last century, the Serbian
scientist Malutin Mealankovich
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. Meanovich
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
Melankovich 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 ahelion when
the planet is furthest from the sun and
perihelion where it is closest. However,
a highly elliptical orbit means that the
Earth's aphhelon 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 Melankovich cycle concerns
the oblquity or tilt of the Earth on its
axis. The more tilted the Earth, the
more extreme the seasons. And this
varies on a roughly 41,000year 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
procession 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 26,000year 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, shorterterm
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
Dansgard Urska 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 pleaene epoch
which spanned from 2.6 million to around
11,700
years ago.
The Ice Age was a time when megapuna
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 animals strategies for
conserving energy. For example,
Bergman'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
largerbodied 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 the 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 imagine.
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 doublecoated fur separated into a
thick underwall 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 savannah or rainforest.
Further aiding their insulation was a
layer of fat up to 9 cm thick and small
haircovered 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
mammoth survived on Wrangler 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 landbridge of Bingia, which
used to connect Alaska and Siberia
before it was submerged under the Arctic
Ocean.
Now on to some of the more obscure
creatures of that glacial period.
The Galiptodont.
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 large, cumbersome creatures
weighing up to two tons and walking on
elephant-sized legs across the Americas.
Their bodies were protected by a huge
turtlike shell or carropus,
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 evolutionwise.
Our aliens would be forgiven for
thinking that these creatures don't get
around much, but recent studies testing
the strength indicators of the
Giptodons'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 by pedily.
This conjures up some even crazier
images. a glytoodont 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 giptoodons might have
been the titans of their time, they are
not around today. Evolution ultimately
replaced them. And honestly, that's a
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The next creature might surprise you as
it still has relatives alive today.
Although we get to meet a mere fraction
of the diversity that our alien
travelers would have seen. The late
pletosene 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 Neoene
before the istmas of Panama formed.
This is probably part of the reason why
they were able to diversify into so many
species since they [music] were exposed
to many different habitats.
Through time, the sloths tended towards
larger sizes. And by the late pletosene,
nature had given birth to a group called
giant ground sloths.
Within this [music] group, Aramtherum
combined the height of a giraffe with
the bulk of an elephant. And the first
described sloth [music] fossil,
Meggathereum Americanum, had an
estimated body mass of [music] 3,800
kg. Our modern-day sloths are puny in
comparison. Their pleaene 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 Aramtherium
sloths of various ages in the sediments
of Tank 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 [music] 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 sloth's wallowing behavior is shared
with many large African mammals alive
today like hippos or rhinos. So it turns
out that the pletoine 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? Mardel Platter 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 plyiosene or late pletosene 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
glosstherum and celidothereum ground
sloths. And there are several reasons
why.
The first clues were the armbbones 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 sloth center
of gravity was found above their hind
feet, which suggests they too could
achieve a bipeedal 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 burers.
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-tooth 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 pleto scene. Between 72
and 88% of these largebodied 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 Wrangler 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 [music] age
journey.
Humans
for the first time ever during their
visits to Earth, our timetraveling
aliens are gazing down on our very own
ancestors.
Homo sapiens evolved around 300,000
years ago, migrating out of Africa to
colonize regions [music] around the
globe.
This means they've lived through a fair
chunk of the pletosene and shared the
land with other ice age creatures of the
time.
So much so that paleontologists and our
aliens are wondering whether we were
responsible for the mega fauna
extinctions at the end of the plea
scene.
Could this be true? Could we have taken
on great woolly mammoths and giant
ground sloths and one? To answer these
questions, the aliens are
[clears throat] 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 [music] 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 [music] can still be seen today.
One of the most impressive described as
the cyine chapel of prehistory was
discovered in Leco Cave in Montgy,
France.
In just a small cave, over 500 painted
and 1,500 engraved images have been
found that were created up to 22,000
years ago.
From these images, you can see that
despiring 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 megapora 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 sapiion 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 megaporna of North
America where they lived.
Another point of contention was the fact
that within a few thousand years of the
globish people arriving in North America
and spreading across the region, the
megapora 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 Cloris
individual, the 18-month-old Anik 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.
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? Megaporna
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 megapora populations. So the
more spores, the more megasized
herbivores there were at the time.
From this data, they found that
megapornal 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 [music]
that broke the mega camel's back, and
their hunting pressure was too intense
for these animals to recover.
Large mammals like the megapora
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
timetraveling 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 megaporna that were
affected. Another mysterious
disappearance in the late pleaene were
then the Neanderthalss who vanished
around 40,000 years ago.
Neanderthalss 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
Neanderthalss 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 Neanderthalss, which
would support the second theory.
As for competition, the latest data
suggests that Neanderthalss and modern
humans coexisted happily for up to
several thousand years in Europe. But
it's 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 energyefficient Homo sapiens to
move in and take over.
Like many debates emerging from this
time period, there's no simple answer
for the Neanderthalss disappearance, and
the situation varies from place to
place. Though we may have been the
better competitor, the Neanderthalss get
a bad rep. 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
timetraveling 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
shortterm scale to the Malankovich
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 [music] 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 amark and both these factors act as
triggers for heinrich events. We've
recently made a video on the amark over
on astramm 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 Melankovich cycle to cause
pleaene 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?
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