The Earth is 4.54 billion years old, plus or minus 50 million years. That’s a lot of
birthdays. In that time, Earth has undergone some pretty incredible changes. In a recent episode,
we covered 4.2 billion years of that history, which saw the Earth transform from a molten
ball of lava to a pale orange wasteland to a giant snowball to a flourishing tropical world.
But Earth’s saga is like a TV drama that keeps taking twists and turns,
with some of the most incredible stuff happening in the last 300 million years.
So, for those of you who were disappointed we didn’t cover dinosaurs in Part One, well, you
might want to stick around. And for anyone just tuning in, here’s our premise: imagine that alien
scientists visited Earth at various stages in its development. What kind of planet would they find?
I’m Alex McColgan and you are watching Astrum. Join me today as we continue Earth’s saga and
imagine how the planet might have looked in its ancient past. First,
a reminder: to answer these questions, we’ll draw on models that not all scientists agree on,
although the job gets easier when our timeline is in millions – rather than billions – of years.
Not all of the science is settled, and some of these models are still being debated. But
to the best of our current knowledge, this is what our planet could have been like.
Now, back to our story… Our intrepid alien scientists are fresh off their exciting trip
to Earth during the Devonian Period and are pretty excited about the direction things are headed.
Obviously, they need to see what happens next. So, they make a return trip 280 million years ago.
Earth is now in its Early Permian Period. The biggest geographical change is that
the continents of Euramerica and Gondwana have combined into a single landmass called Pangaea.
The collision of these large continents, called the Variscan orogeny, unleashes
powerful tectonic forces that create a mountain range called the Central Pangaean Mountains.
How tall are they? Well, Mount Everest is in the right ballpark, as this range is comparable in
size to the modern Himalayas. In fact, they are so tall that they have a profound effect on the
climate of Pangaea. Located near the Earth’s equator, the Central Pangaean Mountains lie
just beneath the Equatorial Rainy Belt. And our alien scientists quickly discover the impact of
these giant mountains on the entire continent. South of the range, it is a megamonsoon climate.
However, there is a flipside to all this rain: the mountain range in turn casts a
rain shadow to the north, which creates a huge desert in Pangaea’s interior.
Basically, when air travels over tall mountains, it moves upward and cools,
causing precipitation, so that by the time it crosses the mountains, the air is pretty arid.
We see this effect today in the Gobi Desert, which is located in the rain shadow of the Himalayas.
Pangaea’s formation is a great example of how plate tectonics not only impact the world’s
landmasses and oceans but its weather as well. Yet there are also other factors shaking up the
world’s climate. During the Early Permian, the Earth is still in the latter days of an
Ice Age dating back tens of millions of years – an event known as the Late Paleozoic Icehouse.
Our leading theory for this cooling is that the explosion of plant life during the Carboniferous
raised Earth’s oxygen levels and diminished its CO-2, leading to a reduction in the
greenhouse effect (with Milankovitch Cycles also likely playing a role.) During the Late
Paleozoic Icehouse, vast glaciers built up at the poles and in the higher elevations.
Yet, by the Early Permian, the planet has begun entering a warming trend.
The polar ice caps are retreating, but glaciers remain in most of the high-elevation mountain
ranges. So, between the climate disruptions caused by Pangaea and the cooler-than-normal-but-warming
global temperatures, lifeforms on Earth have had a lot of adjustments to make.
Since our aliens last visited, the formation of Pangaea has produced a vast super ocean
called the Panthalassic, or “universal sea,” as well a smaller ocean called the Paleo-Tethys.
The Panthalassic is so big, it occupies almost 70% of Earth’s surface! To gather more information,
and, if possible, see what’s down there with their own eyes, our aliens enter a submersible and dive
in. As it turns out, the safety provided by said vehicle is much needed. While harmless trilobites
and nautili remain in abundance, Earth’s oceans also have some terrifying new inhabitants.
Among them is one of the strangest predators ever to patrol the watery depths – helicoprion,
an 8-meter-long sharklike fish with a whorl of teeth in its lower jaw resembling a buzzsaw.
Most likely, this whorl is an adaptation for tearing apart and sucking soft-bodied prey.
Our aliens have seen some strange creatures during their interstellar travels, but this
is definitely one of the strangest. And honestly, helicoprion would look utterly alien to us, too.
I, personally, have always dreamed of a day when humans discover extraterrestrial
life. But until that day comes, our best resource for understanding how life can
evolve under various conditions is Earth’s own fossil record.
Earth was a different planet back then! In our own solar system, moons such as Europa,
Ganymede and Enceladus may have subsurface oceans suitable for such strange lifeforms. Meanwhile,
on land, insects have begun to flex some serious muscle. There are all sorts of beetles,
including permocupedae, and meganisoptera, an extinct order of giant dragonflies. (Just imagine
a dragonfly with a wingspan about the size of a common seagull’s and you’ll get the idea.)
Another, frankly bizarre, newcomer is diplocaulus, an early amphibian with a boomerang-shaped head.
“Look at how fascinating these Earth aliens are!”, I can hear our extraterrestrial xenozoologist say.
But by far, the most interesting quadruped of the Early Permian is the dimetrodon.
Although it is often mistaken for a dinosaur in the popular imagination, this 2-4-meter
sail-backed predator is actually a synapsid, more closely related to modern mammals than reptiles.
Believe it or not, the sail could be an adaptation that predates the transition from exotherms,
or animals that absorb heat from their environment, to endotherms,
which regulate temperature internally. (You know, warm-blooded creatures like you and me.)
Dimetrodon’s sail contains a network of blood vessels, which allows it to raise its temperature
more quickly in sunlight – an early step toward temperature regulation. On a planet experiencing
all kinds of climatic changes, this ability to regulate temperature would certainly be
advantageous . It’s a wonderful illustration of how much living organisms can and must change in
order to survive. Our planet’s climate is like a complex system full of inputs with a biosphere
as corresponding outputs. Planets like ours dictate what sort of life can exist on them.
And interestingly, as a planet changes over time, the type of life it can support also changes.
Impressed by Earth’s development, our alien scientists decide to return in another hundred
million years. Unbeknownst to them, they will miss the largest extinction event in
Earth’s history – and I’m not talking about the asteroid that eventually kills off the dinosaurs.
A much more catastrophic extinction takes place around 252 million years ago, called the Permian
Triassic Extinction Event. Our leading theory is that volcanic eruptions release huge amounts of
CO-2 into the atmosphere, which raise global temperatures and make the oceans more acidic.
This catastrophic event eradicates about 70% of terrestrial vertebrate species and 80% of
all marine species, a mass die-off unmatched by any other in the history of the planet.
Yet, as devastating as this is in the short term, it would eventually clear the field for
a whole lot of evolutionary diversification during the Triassic and Jurassic. And chief
among the beneficiaries is a group of reptiles that would one day rule the planet – dinosaurs.
Our alien scientists return to Earth during the Late Jurassic Period, 150 million years ago.
Although Pangaea managed to hang around until the Early Jurassic,
by now, it is starting to drift apart, due to tectonic movements in the planet’s lithosphere.
The Earth is made up of about 15 to 20 tectonic plates, which are always moving
toward or away from each other at the rate of about 1.5 centimetres a year.
(Which, interestingly enough, is pretty much the same rate that our toenails grow!)
As plates move away from each other, they open a rift marked by outpouring basaltic lava.
So, beginning around 200 million years ago, Laurasia breaks away from Gondwana, creating two
smaller supercontinents: in the North, Laurasia contains modern-day North America and Eurasia;
to the South, Gondwana includes modern-day South America, Africa, Australia, India and Antarctica.
A narrow body of water called the Tethys Sea is also opening up. It will one day
grow into the North Atlantic Ocean, as outpouring basalt lavas at the Mid-Atlantic
Ridge continue to push the landmasses farther apart. Meanwhile, in the South,
Antarctica and Madagascar have begun to separate from Africa, opening up the proto-Indian Ocean.
While the continental landmasses still look quite different from how they look today, our
alien visitors already have an inkling of where Earth’s continental configuration is heading.
The climate of the period is scorching hot. Global temperatures are 5 to 10 degrees warmer
than they are today, with atmospheric CO-2 levels approximately 4 times greater. What
contributed to all this CO-2? Very likely, the mass-extinction of plants during both the Permian
Triassic Extinction Event and a subsequent die-off called the End Triassic Extinction played hefty
roles. Global temperatures are so warm that ice sheets are unable to form at the poles. Instead,
the poles are covered in forests, which likely experience warm summers and cool, snowy winters.
With so little water locked up in glacial ice, sea levels are significantly higher than they are
today, with the peak happening right around this time – about 140 meters higher! In terms of flora,
gymnosperms such as conifers have become one of the most successful plant types. Some trees,
like the extinct Araucaria mirabilis, represented by this extraordinarily well-preserved cone,
look eerily similar to what you’d find today. This is also a golden age for cycads – palmlike
vegetation with woody cylindrical trunks and stiff pinnate leaves. These plants
grow heartily in the Late Jurassic’s expansive tropical and subtropical climate zones. As our
alien scientists step out of their ship, they hear an ominous rumbling. Looking over,
they spot a pack of towering sauropods. Not just any sauropods, either – supersaurus,
one of the most massive terrestrial animals in Earth’s history – measuring up to 35 meters long
and weighing 40 metric tons. Getting over their initial fright, our alien visitors realize that
these goliaths are in fact herbivorous grazers, well adapted for reaching high vegetation.
But their relief is short-lived. Stalking some of the smaller sauropods is a rangy allosaurus,
a formidable species of carnosaur nearly 10 meters long, with dozens of needle-sharp serrated teeth.
Luckily, our alien visitors escape their brush with the hungry carnosaur and decide to finish
the rest of their tour from the safety of their ship. Once they’re in the air,
they encounter a feathered archaeopteryx, an avian dinosaur considered to be one of the first birds.
Archaeopteryx is also sharing the skies with large flocks of non-avian pterosaurs, such as
dimorphodon and the crested Pterodactylus. These winged predators are well adapted for catching
smaller animals and invertebrates in their toothy, beak-like jaws. But as our alien scientists stop
their expedition for lunch in one of the more sheltered forest glades, it’s something small and
unassuming emerging from a burrow that catches the xenozoologist’s interest again – a small, furry
creature called taeniolabis. Taeniolabis and other members of the extinct order multituberculates
(named after their unusual teeth, which they’d use to chew in a forward-and-back grinding motion)
are some of the earliest mammals. And while they may look unassuming, our aliens quickly realize
there’s something different about them as they observe their sociability and the way they play
with one another. These little rodent-like creatures have highly developed brains,
especially compared to pea-brained dinosaurs, and they are warm-blooded, with a useful adaptation
called fur to keep them insulated. Little do our alien visitors know, the great-great-great
descendants of these humble, scurrying creatures will one day outlive the dinosaurs and dominate
the Earth. But that chapter will have to wait for a return trip by our intrepid travellers. They’re
worn out from the scrapes and scares of this trip, but they certainly have an idea of Earth’s immense
diversity and adaptability. Who knows? They may come back to finish the story another day.
I hope you enjoyed this second chapter of Earth’s planetary evolution. Are you
interested in learning more about Earth’s history in future episodes? Which parts
of Earth’s history would you like to visit if you could? Please let me know in the comments.
If you’re an alien scientist exploring an ancient planet, or a human watching a video about it,
sometimes how you explore can be just as important as what you explore. Having an internet browser
that’s cluttered with tabs can be a real energy drain, which is why I’d like to talk to you about
Opera One – the desktop browser that’s the sponsor of today’s video. I’ve never seen a browser that
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the hassle of picking and paying for one. Opera One has a FREE one integrated out of the box. It
also has an adblocker that changes your browsing experience forever. Look at this page before and
after turning on the ad block. Chaos into order. But to me the coolest thing was Aria,
its AI assistant that was integrated right into the browser, available with just a click.
Selecting things on the page allowed me to ask Aria to explain and delve into it, which is a
level of integration I’d never seen before but seemed really enjoyable. Why not try out Opera
One for yourself by downloading it using my link in the description below; I highly recommend it!
Thanks for watching! Did you miss the previous episode about Earth’s past? Check it out here.
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All the best and see you next time.